Answer: log-periodic dipole array

Context: However a log-periodic dipole array consists of a number of dipole elements of different lengths in order to obtain a somewhat directional antenna having an extremely wide bandwidth: these are frequently used for television reception in fringe areas. The dipole antennas composing it are all considered "active elements" since they are all electrically connected together (and to the transmission line). On the other hand, a superficially similar dipole array, the Yagi-Uda Antenna (or simply "Yagi"), has only one dipole element with an electrical connection; the other so-called parasitic elements interact with the electromagnetic field in order to realize a fairly directional antenna but one which is limited to a rather narrow bandwidth. The Yagi antenna has similar looking parasitic dipole elements but which act differently due to their somewhat different lengths. There may be a number of so-called "directors" in front of the active element in the direction of propagation, and usually a single (but possibly more) "reflector" on the opposite side of the active element.

Question: What type of antenna formation is made up of multiple dipole elements of varying lengths?


Answer: extremely wide bandwidth

Question: What is the benefit of this formation type?


Answer: Yagi-Uda Antenna

Question: What is a variation of this antenna type?


Answer: television reception

Question: What is the main application of these set ups?


Answer: vertical

Context: At low frequencies (such as AM broadcast), arrays of vertical towers are used to achieve directionality and they will occupy large areas of land. For reception, a long Beverage antenna can have significant directivity. For non directional portable use, a short vertical antenna or small loop antenna works well, with the main design challenge being that of impedance matching. With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance; small loop antennas are tuned with parallel capacitors for this purpose.

Question: For radio broadcast that one would hear in their car what type of towers are used?


Answer: short vertical antenna

Question: If one wished to take an antenna to different locations, which type would be best?


Answer: achieve directionality

Question: Why is this specific antenna type used?


Answer: impedance matching

Question: What is a problem one might encounter when using a portable antenna?


Answer: antenna lead-in

Context: An antenna lead-in is the transmission line (or feed line) which connects the antenna to a transmitter or receiver. The antenna feed may refer to all components connecting the antenna to the transmitter or receiver, such as an impedance matching network in addition to the transmission line. In a so-called aperture antenna, such as a horn or parabolic dish, the "feed" may also refer to a basic antenna inside the entire system (normally at the focus of the parabolic dish or at the throat of a horn) which could be considered the one active element in that antenna system. A microwave antenna may also be fed directly from a waveguide in place of a (conductive) transmission line.

Question: What is mainly responsible for the connection of the antenna to its end destinations?


Answer: antenna feed

Question: What is the group of elements used to join the elements of an antenna?


Answer: aperture antenna

Question: What are the type of antennas used with satellite television called?


Answer: microwave antenna

Question: What can be used in place of a standard transmission line?


Answer: metal rod

Context: Monopole antennas consist of a single radiating element such as a metal rod, often mounted over a conducting surface, a ground plane. One side of the feedline from the receiver or transmitter is connected to the rod, and the other side to the ground plane, which may be the Earth. The most common form is the quarter-wave monopole which is one-quarter of a wavelength long and has a gain of 5.12 dBi when mounted over a ground plane. Monopoles have an omnidirectional radiation pattern, so they are used for broad coverage of an area, and have vertical polarization. The ground waves used for broadcasting at low frequencies must be vertically polarized, so large vertical monopole antennas are used for broadcasting in the MF, LF, and VLF bands. Small monopoles are used as nondirectional antennas on portable radios in the HF, VHF, and UHF bands.

Question: Monopole antennas consist of what element?


Answer: nondirectional antennas

Question: What are small monopoles used as?


Answer: quarter-wave monopole

Question: What the most common form?


Answer: Monopoles

Question: What has vertical polarization?


Answer: dipole antenna

Context: The most widely used class of antenna, a dipole antenna consists of two symmetrical radiators such as metal rods or wires, with one side of the balanced feedline from the transmitter or receiver attached to each. A horizontal dipole radiates in two lobes perpendicular to the antenna's axis. A half-wave dipole the most common type, has two collinear elements each a quarter wavelength long and a gain of 2.15 dBi. Used individually as low gain antennas, dipoles are also used as driven elements in many more complicated higher gain types of antennas.

Question: What is the most widley used antenna class?


Answer: horizontal dipole

Question: What radiates two lobes perpendicular to the antennas axis?


Answer: dipoles

Question: Besides low gain antennas, what is also used as driven elements in complicated higher gain types of antennas?


Answer: 2.15 dBi

Question: How much gain does a half-wave dipole have?


Answer: linear and reciprocal

Context: A necessary condition for the aforementioned reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral) means that the material has the same response to an electric current or magnetic field in one direction, as it has to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as isolators and circulators, made of nonreciprocal materials such as ferrite. These can be used to give the antenna a different behavior on receiving than it has on transmitting, which can be useful in applications like radar.

Question: What must be true of the antenna and transmission medium for the repiprocity rule to apply ?


Answer: ferrite

Question: What is one material that does not have this quality?


Answer: radar

Question: How can the lack of this quality be used in an everyday way?


Answer: Reciprocal

Question: What is called when the direction of the elctrical current does not make a difference to the current?


Answer: performance measures

Context: Antennas are characterized by a number of performance measures which a user would be concerned with in selecting or designing an antenna for a particular application. Chief among these relate to the directional characteristics (as depicted in the antenna's radiation pattern) and the resulting gain. Even in omnidirectional (or weakly directional) antennas, the gain can often be increased by concentrating more of its power in the horizontal directions, sacrificing power radiated toward the sky and ground. The antenna's power gain (or simply "gain") also takes into account the antenna's efficiency, and is often the primary figure of merit.

Question: How could one deide what type of antenna is nedded for a project?


Answer: directional characteristics

Question: What would most likely be the main concern in making this decision?


Answer: horizontal directions

Question: How would you distribute power to allow for a greater gain?


Answer: efficiency

Question: What is often the most imprtant crediting factor of antennas?


Answer: Resonant antennas

Context: Resonant antennas are expected to be used around a particular resonant frequency; an antenna must therefore be built or ordered to match the frequency range of the intended application. A particular antenna design will present a particular feedpoint impedance. While this may affect the choice of an antenna, an antenna's impedance can also be adapted to the desired impedance level of a system using a matching network while maintaining the other characteristics (except for a possible loss of efficiency).

Question: Which antenna type would be best for a project requiring a specific frequency?


Answer: built or ordered

Question: How could an antenna be made to coordinate with the needed frequency?


Answer: particular antenna design

Question: What factor would result in a desired feedback independence?


Answer: matching network

Question: If you were unable to choose the antenna you wanted how could you still achieve this result?


Answer: polarization

Context: An antenna transmits and receives radio waves with a particular polarization which can be reoriented by tilting the axis of the antenna in many (but not all) cases. The physical size of an antenna is often a practical issue, particularly at lower frequencies (longer wavelengths). Highly directional antennas need to be significantly larger than the wavelength. Resonant antennas usually use a linear conductor (or element), or pair of such elements, each of which is about a quarter of the wavelength in length (an odd multiple of quarter wavelengths will also be resonant). Antennas that are required to be small compared to the wavelength sacrifice efficiency and cannot be very directional. Fortunately at higher frequencies (UHF, microwaves) trading off performance to obtain a smaller physical size is usually not required.

Question: What is the essential difference in radio waves transmitted by an antenna?


Answer: tilting the axis

Question: How can this be adjusted more easily than changing antenna types?


Answer: at lower frequencies

Question: When might the size of an antenna cause an issue?


Answer: small

Question: What size antenna would not be good when the antenna needs to be directional?


Answer: Highly directional

Question: There is a relationship between the size of the antenna and the size of the wavelength with what antenna type?


Answer: electrons

Context: The majority of antenna designs are based on the resonance principle. This relies on the behaviour of moving electrons, which reflect off surfaces where the dielectric constant changes, in a fashion similar to the way light reflects when optical properties change. In these designs, the reflective surface is created by the end of a conductor, normally a thin metal wire or rod, which in the simplest case has a feed point at one end where it is connected to a transmission line. The conductor, or element, is aligned with the electrical field of the desired signal, normally meaning it is perpendicular to the line from the antenna to the source (or receiver in the case of a broadcast antenna).

Question: What particle's migration does the resonance principle rely on?


Answer: resonance principle

Question: What is the basis for the way most antennas are developed?


Answer: reflective

Question: What type of surface is formed by the tip of a conductor?


Answer: perpendicular

Question: How would you place the conductor in relation to the signal you wished to obtain?


Answer: electrical component

Context: The radio signal's electrical component induces a voltage in the conductor. This causes an electrical current to begin flowing in the direction of the signal's instantaneous field. When the resulting current reaches the end of the conductor, it reflects, which is equivalent to a 180 degree change in phase. If the conductor is 1⁄4 of a wavelength long, current from the feed point will undergo 90 degree phase change by the time it reaches the end of the conductor, reflect through 180 degrees, and then another 90 degrees as it travels back. That means it has undergone a total 360 degree phase change, returning it to the original signal. The current in the element thus adds to the current being created from the source at that instant. This process creates a standing wave in the conductor, with the maximum current at the feed.

Question: What part of the radio signal creates voltage?


Answer: instantaneous field

Question: What would the electric current always gravitate to?


Answer: 180 degree change in phase

Question: What is the outcome when a curren is reflected>


Answer: 360 degree

Question: What amount of phase change would return a signal to its originial state?


Answer: half-wave dipole

Context: The ordinary half-wave dipole is probably the most widely used antenna design. This consists of two 1⁄4-wavelength elements arranged end-to-end, and lying along essentially the same axis (or collinear), each feeding one side of a two-conductor transmission wire. The physical arrangement of the two elements places them 180 degrees out of phase, which means that at any given instant one of the elements is driving current into the transmission line while the other is pulling it out. The monopole antenna is essentially one half of the half-wave dipole, a single 1⁄4-wavelength element with the other side connected to ground or an equivalent ground plane (or counterpoise). Monopoles, which are one-half the size of a dipole, are common for long-wavelength radio signals where a dipole would be impractically large. Another common design is the folded dipole, which is essentially two dipoles placed side-by-side and connected at their ends to make a single one-wavelength antenna.

Question: What is the most popular antenna type?


Answer: transmission line

Question: What is the current usually beng put into it or pulled out of?


Answer: collinear

Question: Elements in a half wave dipole and on an identical axis are said to be what?


Answer: Monopoles

Question: What antenna type is a portion of the half wave dipole?


Answer: folded dipole

Question: What popular type combines more that one antenna?


Answer: f0

Context: The standing wave forms with this desired pattern at the design frequency, f0, and antennas are normally designed to be this size. However, feeding that element with 3f0 (whose wavelength is 1⁄3 that of f0) will also lead to a standing wave pattern. Thus, an antenna element is also resonant when its length is 3⁄4 of a wavelength. This is true for all odd multiples of 1⁄4 wavelength. This allows some flexibility of design in terms of antenna lengths and feed points. Antennas used in such a fashion are known to be harmonically operated.

Question: What frequency are antennas normally designed to be?


Answer: 3f0

Question: What can be added to f0 to create a standing wave pattern?


Answer: 1⁄4

Question: What multiple is essential for wavelengths?


Answer: harmonically

Question: How are waves which are used in the ways discussed controlled?


Answer: imitate

Context: The quarter-wave elements imitate a series-resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and voltage node (minimum) at the feed. In electrical terms, this means the element has minimum reactance, generating the maximum current for minimum voltage. This is the ideal situation, because it produces the maximum output for the minimum input, producing the highest possible efficiency. Contrary to an ideal (lossless) series-resonant circuit, a finite resistance remains (corresponding to the relatively small voltage at the feed-point) due to the antenna's radiation resistance as well as any actual electrical losses.

Question: How do quarter wave elements act in relation to a series relevant electrical element?


Answer: resonant frequency

Question: What frequency develops a current peak?


Answer: minimum reactance

Question: How would you describe a current that has maximum efficiency?


Answer: lossless

Question: What could be the best possible output versus input ratio?


Answer: impedance matching

Context: It is possible to use the impedance matching concepts to construct vertical antennas substantially shorter than the 1⁄4 wavelength at which the antenna is resonant. By adding an inductance in series with the antenna, a so-called loading coil, the capacitive reactance of this antenna can be cancelled leaving a pure resistance which can then be matched to the transmission line. Sometimes the resulting resonant frequency of such a system (antenna plus matching network) is described using the construct of electrical length and the use of a shorter antenna at a lower frequency than its resonant frequency is termed electrical lengthening.

Question: For use with more than one channel changes are made to increase what property?


Answer: inductance

Question: What could be coupled with an antenna to form pure resistance?


Answer: transmission line

Question: What element would this pure resistance be coupled with?


Answer: electrical lengthening

Question: What phrase describes the process of purposely using a lower standing antenna at a less than peak frequency?


Answer: resonant multiples

Context: The end result is that the resonant antenna will efficiently feed a signal into the transmission line only when the source signal's frequency is close to that of the design frequency of the antenna, or one of the resonant multiples. This makes resonant antenna designs inherently narrowband, and they are most commonly used with a single target signal. They are particularly common on radar systems, where the same antenna is used for both broadcast and reception, or for radio and television broadcasts, where the antenna is working with a single frequency. They are less commonly used for reception where multiple channels are present, in which case additional modifications are used to increase the bandwidth, or entirely different antenna designs are used.

Question: If your were unable to match the source frequency with the design frequency of the antenna what could you use?


Answer: single target signal

Question: What is the most common application of resonant antennas?


Answer: resonant

Question: What antenna setup type is generally used for TV viewing?


Answer: bandwidth

Question: For use with more than one channel changes are made to increase what property?


Answer: inverse square law

Context: The amount of signal received from a distant transmission source is essentially geometric in nature due to the inverse square law, and this leads to the concept of effective area. This measures the performance of an antenna by comparing the amount of power it generates to the amount of power in the original signal, measured in terms of the signal's power density in Watts per square metre. A half-wave dipole has an effective area of 0.13 2. If more performance is needed, one cannot simply make the antenna larger. Although this would intercept more energy from the signal, due to the considerations above, it would decrease the output significantly due to it moving away from the resonant length. In roles where higher performance is needed, designers often use multiple elements combined together.

Question: What accounts for the geometry involved in the use of an antenna?


Answer: Watts per square metre

Question: How is the compactness of the signal measured?


Answer: higher performance

Question: What type of project would call for more than one element used together?


Answer: feed point

Context: Returning to the basic concept of current flows in a conductor, consider what happens if a half-wave dipole is not connected to a feed point, but instead shorted out. Electrically this forms a single 1⁄2-wavelength element. But the overall current pattern is the same; the current will be zero at the two ends, and reach a maximum in the center. Thus signals near the design frequency will continue to create a standing wave pattern. Any varying electrical current, like the standing wave in the element, will radiate a signal. In this case, aside from resistive losses in the element, the rebroadcast signal will be significantly similar to the original signal in both magnitude and shape. If this element is placed so its signal reaches the main dipole in-phase, it will reinforce the original signal, and increase the current in the dipole. Elements used in this way are known as passive elements.

Question: What is a half wave dipole need to be coupled with in most instances?


Answer: center

Question: What part of the current is usually strongest?


Answer: standing wave pattern

Question: What does this result in?


Answer: passive elements

Question: Element used to provide support to the original signal are called?


Answer: Yagi-Uda array

Context: A Yagi-Uda array uses passive elements to greatly increase gain. It is built along a support boom that is pointed toward the signal, and thus sees no induced signal and does not contribute to the antenna's operation. The end closer to the source is referred to as the front. Near the rear is a single active element, typically a half-wave dipole or folded dipole. Passive elements are arranged in front (directors) and behind (reflectors) the active element along the boom. The Yagi has the inherent quality that it becomes increasingly directional, and thus has higher gain, as the number of elements increases. However, this also makes it increasingly sensitive to changes in frequency; if the signal frequency changes, not only does the active element receive less energy directly, but all of the passive elements adding to that signal also decrease their output as well and their signals no longer reach the active element in-phase.

Question: What can take advantage of these elements to add more gain?


Answer: does not contribute

Question: Does this device improve the operation of the antenna?


Answer: directors

Question: What is the name for passive elements nearer to the source of the signal?


Answer: increasingly directional

Question: Adding more elements to a Yagi-Uda would have what effect?


Answer: active elements

Context: It is also possible to use multiple active elements and combine them together with transmission lines to produce a similar system where the phases add up to reinforce the output. The antenna array and very similar reflective array antenna consist of multiple elements, often half-wave dipoles, spaced out on a plane and wired together with transmission lines with specific phase lengths to produce a single in-phase signal at the output. The log-periodic antenna is a more complex design that uses multiple in-line elements similar in appearance to the Yagi-Uda but using transmission lines between the elements to produce the output.

Question: What can be paired with transmission lines to create phases that would support output?


Answer: half-wave dipoles

Question: What is the most common element used to create a single in phase signal?


Answer: phase lengths

Question: What must be precise in order to create this signal at output?


Answer: log-periodic

Question: What is a more complicated occurrence of the single in-phase producing antenna?


Answer: extended conductive surface

Context: Reflection of the original signal also occurs when it hits an extended conductive surface, in a fashion similar to a mirror. This effect can also be used to increase signal through the use of a reflector, normally placed behind the active element and spaced so the reflected signal reaches the element in-phase. Generally the reflector will remain highly reflective even if it is not solid; gaps less than 1⁄10 generally have little effect on the outcome. For this reason, reflectors often take the form of wire meshes or rows of passive elements, which makes them lighter and less subject to wind. The parabolic reflector is perhaps the best known example of a reflector-based antenna, which has an effective area far greater than the active element alone.

Question: If you wanted to somehow clone the original signal you could use?


Answer: increase

Question: What effect would the use of a reflector have on a signal?


Answer: less than 1⁄10

Question: What allowance can be made for gaps without loss of performance?


Answer: parabolic reflector

Question: What is the most recognized type of an antenna that has its basis in reflection?


Answer: a capacitor at the frequency of operation

Context: Another extreme case of impedance matching occurs when using a small loop antenna (usually, but not always, for receiving) at a relatively low frequency where it appears almost as a pure inductor. Resonating such an inductor with a capacitor at the frequency of operation not only cancels the reactance but greatly magnifies the very small radiation resistance of such a loop.[citation needed] This is implemented in most AM broadcast receivers, with a small ferrite loop antenna resonated by a capacitor which is varied along with the receiver tuning in order to maintain resonance over the AM broadcast band

Question: What magnifies the small radiation resistance of a loop?


Answer: small ferrite loop antenna

Question: What is resonated by a capacitor along with the receiver tuning that maintains resonance over the AM broadcast band?


Answer: loop

Question: What is used in most AM broadcaster receivers?


Answer: impedance matching

Question: When using a small loop antenna at a low frequency, what may occur?


Answer: resistive impedance

Context: Antenna tuning generally refers to cancellation of any reactance seen at the antenna terminals, leaving only a resistive impedance which might or might not be exactly the desired impedance (that of the transmission line). Although an antenna may be designed to have a purely resistive feedpoint impedance (such as a dipole 97% of a half wavelength long) this might not be exactly true at the frequency that it is eventually used at. In some cases the physical length of the antenna can be "trimmed" to obtain a pure resistance. On the other hand, the addition of a series inductance or parallel capacitance can be used to cancel a residual capacitative or inductive reactance, respectively.

Question: What is left after antenna tuning?


Answer: antenna terminals

Question: Where does cancellation of any reactance seen?


Answer: parallel capacitance

Question: What can be used to cancel a inductibe reactance or residual capacitative?


Answer: purely resistive feedpoint

Question: What is an antenna designed to have?


Answer: resonant

Context: Although a resonant antenna has a purely resistive feed-point impedance at a particular frequency, many (if not most) applications require using an antenna over a range of frequencies. An antenna's bandwidth specifies the range of frequencies over which its performance does not suffer due to a poor impedance match. Also in the case of a Yagi-Uda array, the use of the antenna very far away from its design frequency reduces the antenna's directivity, thus reducing the usable bandwidth regardless of impedance matching.

Question: What type of antenna has impedance at a specific frequency?


Answer: bandwidth

Question: What term can be used to refer to the usable spectrum of an antennas frequency?


Answer: impedance match

Question: What causes the frequencies outside of the bandwidth to be unusable?


Answer: directivity

Question: What is lessened by the Yagi-Uda design?


Answer: diameter

Context: Instead, it is often desired to have an antenna whose impedance does not vary so greatly over a certain bandwidth. It turns out that the amount of reactance seen at the terminals of a resonant antenna when the frequency is shifted, say, by 5%, depends very much on the diameter of the conductor used. A long thin wire used as a half-wave dipole (or quarter wave monopole) will have a reactance significantly greater than the resistive impedance it has at resonance, leading to a poor match and generally unacceptable performance. Making the element using a tube of a diameter perhaps 1/50 of its length, however, results in a reactance at this altered frequency which is not so great, and a much less serious mismatch which will only modestly damage the antenna's net performance. Thus rather thick tubes are typically used for the solid elements of such antennas, including Yagi-Uda arrays.

Question: What characteristic of the conductor changes the amount of reactance?


Answer: reactance

Question: What characteristic would be better if it were steady?


Answer: A long thin wire

Question: What would be used to create a half wave or quarter wave dipole?


Answer: thick tubes

Question: What type of tubes are generally used for sturdier always of antennas?


Answer: widens

Context: Rather than just using a thick tube, there are similar techniques used to the same effect such as replacing thin wire elements with cages to simulate a thicker element. This widens the bandwidth of the resonance. On the other hand, amateur radio antennas need to operate over several bands which are widely separated from each other. This can often be accomplished simply by connecting resonant elements for the different bands in parallel. Most of the transmitter's power will flow into the resonant element while the others present a high (reactive) impedance and draw little current from the same voltage. A popular solution uses so-called traps consisting of parallel resonant circuits which are strategically placed in breaks along each antenna element. When used at one particular frequency band the trap presents a very high impedance (parallel resonance) effectively truncating the element at that length, making it a proper resonant antenna. At a lower frequency the trap allows the full length of the element to be employed, albeit with a shifted resonant frequency due to the inclusion of the trap's net reactance at that lower frequency.

Question: What effect do cages have on the spectrum of usable frequencies?


Answer: cages

Question: What type of tubes are generally used for sturdier always of antennas?


Answer: connecting resonant elements

Question: How could one achieve the task of creating an antenna that can be Used over various bands?


Answer: trap's

Question: What is an essential for dealing with directing the flow of power?


Answer: gain

Context: Gain is a parameter which measures the degree of directivity of the antenna's radiation pattern. A high-gain antenna will radiate most of its power in a particular direction, while a low-gain antenna will radiate over a wider angle. The antenna gain, or power gain of an antenna is defined as the ratio of the intensity (power per unit surface area) radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by the intensity radiated at the same distance by a hypothetical isotropic antenna which radiates equal power in all directions. This dimensionless ratio is usually expressed logarithmically in decibels, these units are called "decibels-isotropic" (dBi)

Question: What is an acknowledgement of the range of possible direction for and antenna?


Answer: power gain

Question: What is another way to refer to an antennas gain?


Answer: power per unit surface area

Question: What is the meaning of intensity?


Answer: isotropic

Question: What type of an antenna would offer the same level of power to each possible destination?


Answer: longer range

Context: High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at the other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant. An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones. Antenna gain should not be confused with amplifier gain, a separate parameter measuring the increase in signal power due to an amplifying device.

Question: Antennas with higher gain have what positive feature?


Answer: amplifier gain

Question: What is a measure of how much efficient is improved by adding a device designed to make something stronger?


Answer: parabolic dish

Question: Dish network Tv takes example of what type of antenna?


Answer: Low-gain

Question: What type of antenna would be best if placement was tricky?


Answer: proportional

Context: Due to reciprocity (discussed above) the gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with no loss, that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ2/4π, the wavelength squared divided by 4π. Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency is equal to 1. Therefore, the effective area Aeff in terms of the gain G in a given direction is given by:

Question: What must the relationship of an antenna and the receiving area be due to reciprocity?


Answer: no loss

Question: what could an antenna with complete electrical efficiency be said to have?


Answer: Aeff

Question: Another term for the effective area is?


Answer: 1

Question: hat could an antenna with complete electrical efficiency be said to have?


Answer: relative field strength

Context: The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles; this is called an omnidirectional pattern and when plotted looks like a torus or donut.

Question: A plot of the radiation behaviors of an antenna would show what?


Answer: three-dimensional graph

Question: What type of pictoral aid is often used to show this?


Answer: isotropic

Question: A sphere shows what type of antennas radiation?


Answer: nondirectional

Question: Dipoles are considered to be what antenna type?


Answer: donut

Question: What would an omnidirectional antenna look like if plotted?


Answer: nulls

Context: The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero. This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive at distant points in phase, and zero radiation at other angles where the radio waves arrive out of phase. In a directional antenna designed to project radio waves in a particular direction, the lobe in that direction is designed larger than the others and is called the "main lobe". The other lobes usually represent unwanted radiation and are called "sidelobes". The axis through the main lobe is called the "principal axis" or "boresight axis".

Question: What is the term that refers to areas where an antennas radiation is zero?


Answer: interfere

Question: What do radio waves do that account for maxima or nulls in an antenna pattern?


Answer: lobe

Question: If you desired to project radio waves to the south, what part of the antenna would you build larger in that direction?


Answer: represent unwanted radiation

Question: What is the main distinction of side lobes?


Answer: radio

Context: As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Question: What is one piece that makes up an antenna system?


Answer: standing wave

Question: What is created by a portion of a radio waves energy reversing?


Answer: standing wave ratio

Question: A term that refers to the highs and lows of power in electro magnetic waves is?


Answer: power transfer

Question: Impedance matching makes an important difference in what antenna function?


Answer: Efficiency

Context: Efficiency of a transmitting antenna is the ratio of power actually radiated (in all directions) to the power absorbed by the antenna terminals. The power supplied to the antenna terminals which is not radiated is converted into heat. This is usually through loss resistance in the antenna's conductors, but can also be due to dielectric or magnetic core losses in antennas (or antenna systems) using such components. Such loss effectively robs power from the transmitter, requiring a stronger transmitter in order to transmit a signal of a given strength.

Question: A measure of the power that is useable and the power absorbed by the terminals?


Answer: heat

Question: What happens to the power that is not absorbed by the antenna?


Answer: magnetic core losses

Question: What can cause that reaction?


Answer: transmitter

Question: What can cause that reaction?


Answer: 100 W

Context: For instance, if a transmitter delivers 100 W into an antenna having an efficiency of 80%, then the antenna will radiate 80 W as radio waves and produce 20 W of heat. In order to radiate 100 W of power, one would need to use a transmitter capable of supplying 125 W to the antenna. Note that antenna efficiency is a separate issue from impedance matching, which may also reduce the amount of power radiated using a given transmitter. If an SWR meter reads 150 W of incident power and 50 W of reflected power, that means that 100 W have actually been absorbed by the antenna (ignoring transmission line losses). How much of that power has actually been radiated cannot be directly determined through electrical measurements at (or before) the antenna terminals, but would require (for instance) careful measurement of field strength. Fortunately the loss resistance of antenna conductors such as aluminum rods can be calculated and the efficiency of an antenna using such materials predicted.

Question: What would need to be placed into the transmitter to create ten W oh warmth?


Answer: electrical measurements

Question: What would need to be investigated to determine how much power was radiated?


Answer: impedance matching

Question: What factor may play a hand in lessened power from a transmitter?


Answer: loss resistance

Context: However loss resistance will generally affect the feedpoint impedance, adding to its resistive (real) component. That resistance will consist of the sum of the radiation resistance Rr and the loss resistance Rloss. If an rms current I is delivered to the terminals of an antenna, then a power of I2Rr will be radiated and a power of I2Rloss will be lost as heat. Therefore, the efficiency of an antenna is equal to Rr / (Rr + Rloss). Of course only the total resistance Rr + Rloss can be directly measured.

Question: What can increase the feedpoint impedance of a component?


Answer: resistance

Question: The addition of Rr and Rloss equals what?


Answer: Rr / (Rr + Rloss)

Question: What equation an determine an antennas effectiveness?


Answer: total resistance

Question: What is the single factor that can be precisely measured?


Answer: thermal noise floor

Context: According to reciprocity, the efficiency of an antenna used as a receiving antenna is identical to the efficiency as defined above. The power that an antenna will deliver to a receiver (with a proper impedance match) is reduced by the same amount. In some receiving applications, the very inefficient antennas may have little impact on performance. At low frequencies, for example, atmospheric or man-made noise can mask antenna inefficiency. For example, CCIR Rep. 258-3 indicates man-made noise in a residential setting at 40 MHz is about 28 dB above the thermal noise floor. Consequently, an antenna with a 20 dB loss (due to inefficiency) would have little impact on system noise performance. The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR).

Question: What is the median level for measuring atmospheric noise?


Answer: receiving

Question: In what type of programs would low efficiency antennas not make a difference in effectiveness?


Answer: man-made noise

Question: At lesser frequencies what can account for incorrect assumptions about efficiency?


Answer: signal to noise ratio

Question: What is SNR?


Answer: antenna gain

Context: The definition of antenna gain or power gain already includes the effect of the antenna's efficiency. Therefore, if one is trying to radiate a signal toward a receiver using a transmitter of a given power, one need only compare the gain of various antennas rather than considering the efficiency as well. This is likewise true for a receiving antenna at very high (especially microwave) frequencies, where the point is to receive a signal which is strong compared to the receiver's noise temperature. However, in the case of a directional antenna used for receiving signals with the intention of rejecting interference from different directions, one is no longer concerned with the antenna efficiency, as discussed above. In this case, rather than quoting the antenna gain, one would be more concerned with the directive gain which does not include the effect of antenna (in)efficiency. The directive gain of an antenna can be computed from the published gain divided by the antenna's efficiency.

Question: What else is also known as power gain?


Answer: transmitter

Question: What is used to signal toward a reciever?


Answer: directive gain

Question: Which gain does not iclude the effect of an antenna?


Answer: published gain

Question: Wats divided by the antennas efficiency?


Answer: inefficient

Context: This is fortunate, since antennas at lower frequencies which are not rather large (a good fraction of a wavelength in size) are inevitably inefficient (due to the small radiation resistance Rr of small antennas). Most AM broadcast radios (except for car radios) take advantage of this principle by including a small loop antenna for reception which has an extremely poor efficiency. Using such an inefficient antenna at this low frequency (530–1650 kHz) thus has little effect on the receiver's net performance, but simply requires greater amplification by the receiver's electronics. Contrast this tiny component to the massive and very tall towers used at AM broadcast stations for transmitting at the very same frequency, where every percentage point of reduced antenna efficiency entails a substantial cost.

Question: Small and minimal frequency antennas are know to be what?


Answer: small loop antenna

Question: What is added to to increase ability for reception?


Answer: little effect

Question: How would this antenna rate in the greater scheme of things?


Answer: substantial cost

Question: When talking about much larger network what effect can reduced antenna effectiveness have?


Answer: one

Context: The polarization of an antenna refers to the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation; note that this designation is totally distinct from the antenna's directionality. Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. As a transverse wave, the magnetic field of a radio wave is at right angles to that of the electric field, but by convention, talk of an antenna's "polarization" is understood to refer to the direction of the electric field.

Question: How many polarizations will a antenna have when mounted vertically?


Answer: E-plane

Question: What is another name for electric-field?


Answer: transverse wave

Question: When is a magnetic fields right angles to a electrical field?


Answer: polarization

Question: Whats understood in reference of direction of an E-plane?


Answer: Reflections

Context: Reflections generally affect polarization. For radio waves, one important reflector is the ionosphere which can change the wave's polarization. Thus for signals received following reflection by the ionosphere (a skywave), a consistent polarization cannot be expected. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Matching the receiving antenna's polarization to that of the transmitter can make a very substantial difference in received signal strength.

Question: What mostly affects polarization?


Answer: ionosphere

Question: What reflector can change the waves polarization?


Answer: transmitter

Question: What will you be matching with the receiving antenna's polarization?


Answer: polarized transmissions

Question: What stays the same regarding polarization state at the recieving location?


Answer: a skywave

Question: What is the name used for signals recieved following reflection by the ionosphere?


Answer: Polarization

Context: Polarization is predictable from an antenna's geometry, although in some cases it is not at all obvious (such as for the quad antenna). An antenna's linear polarization is generally along the direction (as viewed from the receiving location) of the antenna's currents when such a direction can be defined. For instance, a vertical whip antenna or Wi-Fi antenna vertically oriented will transmit and receive in the vertical polarization. Antennas with horizontal elements, such as most rooftop TV antennas in the United States, are horizontally polarized (broadcast TV in the U.S. usually uses horizontal polarization). Even when the antenna system has a vertical orientation, such as an array of horizontal dipole antennas, the polarization is in the horizontal direction corresponding to the current flow. The polarization of a commercial antenna is an essential specification.

Question: Whats predictable about an antenna's geometry?


Answer: commercial antenna

Question: The polarization of what antenna is essential specification?


Answer: horizontal

Question: Most rooftop antenna's are polarized in which direction?


Answer: quad antenna

Question: What is a more complicated type of polarization from an antenna's geometry?


Answer: imaginary plane

Context: Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the "thumb in the direction of the propagation" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.

Question: What are electrical fields projected on to?


Answer: radio wave

Question: What is the imagenary plane perpindicular to?


Answer: elliptical

Question: What is the name to describe polarization of radio waves varies over times?


Answer: one direction

Question: How many directions does the E-plane of the radio waves oscillates back and forth?


Answer: match the polarization

Context: It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations. Transmission from a circularly polarized antenna received by a linearly polarized antenna (or vice versa) entails a 3 dB reduction in signal-to-noise ratio as the received power has thereby been cut in half.

Question: What is the best for an recieving antenna for optimum reception?


Answer: Intermediate matchings

Question: What loses signal strength?


Answer: circularly polarized

Question: What is used to match vertical and horizontal linear polarizations?


Answer: signal-to-noise ratio

Question: A transmission can cause reduction in what?


Answer: Maximum power transfer

Context: Maximum power transfer requires matching the impedance of an antenna system (as seen looking into the transmission line) to the complex conjugate of the impedance of the receiver or transmitter. In the case of a transmitter, however, the desired matching impedance might not correspond to the dynamic output impedance of the transmitter as analyzed as a source impedance but rather the design value (typically 50 ohms) required for efficient and safe operation of the transmitting circuitry. The intended impedance is normally resistive but a transmitter (and some receivers) may have additional adjustments to cancel a certain amount of reactance in order to "tweak" the match. When a transmission line is used in between the antenna and the transmitter (or receiver) one generally would like an antenna system whose impedance is resistive and near the characteristic impedance of that transmission line in order to minimize the standing wave ratio (SWR) and the increase in transmission line losses it entails, in addition to supplying a good match at the transmitter or receiver itself.

Question: What requires matching of the empedance to an antenna system?


Answer: "tweak" the match

Question: Why would a transmitter have additional adjustments?


Answer: standing wave ratio

Question: What is SWR?


Answer: 50 ohms

Question: What is the desired design value for transmmiting circuitry?


Answer: whip antenna

Context: In some cases this is done in a more extreme manner, not simply to cancel a small amount of residual reactance, but to resonate an antenna whose resonance frequency is quite different from the intended frequency of operation. For instance, a "whip antenna" can be made significantly shorter than 1/4 wavelength long, for practical reasons, and then resonated using a so-called loading coil. This physically large inductor at the base of the antenna has an inductive reactance which is the opposite of the capacitative reactance that such a vertical antenna has at the desired operating frequency. The result is a pure resistance seen at feedpoint of the loading coil; unfortunately that resistance is somewhat lower than would be desired to match commercial coax.[citation needed]

Question: What can be shorter than 1/4 wavelength long?


Answer: capacitative reactance

Question: What is the opposite of inductive reactance?


Answer: loading coil

Question: What is at the base of the antenna?


Answer: feedpoint

Question: Where is the resistance seen on the loading foil?


Answer: turns ratio

Context: So an additional problem beyond canceling the unwanted reactance is of matching the remaining resistive impedance to the characteristic impedance of the transmission line. In principle this can always be done with a transformer, however the turns ratio of a transformer is not adjustable. A general matching network with at least two adjustments can be made to correct both components of impedance. Matching networks using discrete inductors and capacitors will have losses associated with those components, and will have power restrictions when used for transmitting. Avoiding these difficulties, commercial antennas are generally designed with fixed matching elements or feeding strategies to get an approximate match to standard coax, such as 50 or 75 Ohms. Antennas based on the dipole (rather than vertical antennas) should include a balun in between the transmission line and antenna element, which may be integrated into any such matching network.

Question: What is not adjustable when it comes to a transformer?


Answer: 50 or 75

Question: How many ohms are in are in a standard coax?


Answer: two adjustments

Question: A general matching network needs a minimum of how many adjustments to correct all components of impedance?


Answer: balun

Question: What is included between the transmission line and the antenna element?


Answer: matching network

Question: A balun should be integrated into what?


Answer: traveling wave antennas

Context: Unlike the above antennas, traveling wave antennas are nonresonant so they have inherently broad bandwidth. They are typically wire antennas multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas.

Question: What antenna's are nonresonant?


Answer: one direction

Question: How long are the wire antenna's that the voltage and current waves travel in the same direction?


Answer: resistor

Question: What are undirectional traveling wave directions terminated by?


Answer: helical antenna

Question: What antenna does not have linear polarization?


Answer: antenna's characteristic resistance

Question: What is the resistor equal to?


Answer: dielectric constant

Context: The radiation pattern and even the driving point impedance of an antenna can be influenced by the dielectric constant and especially conductivity of nearby objects. For a terrestrial antenna, the ground is usually one such object of importance. The antenna's height above the ground, as well as the electrical properties (permittivity and conductivity) of the ground, can then be important. Also, in the particular case of a monopole antenna, the ground (or an artificial ground plane) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.

Question: What is the radiation patter influenced by?


Answer: terrestrial antenna

Question: The ground is important for what antenna?


Answer: artificial ground plane

Question: Whats another name for the ground?


Answer: return connection

Question: What does the artificial ground plane do for the antenna current?


Answer: topography

Context: The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.

Question: What is the net quality of the ground dependent of?


Answer: reflection

Question: What is the reason for the receiver seeing both the ral antenna and image of the antenna?


Answer: higher frequencies

Question: What frequencies is associated with shorter wavelengths?


Answer: ground has irregularities

Question: When will reflections not be coherent?


Answer: n=2

Context: The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n=2) compared to air (n=1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of radians or 180°). On the other hand, the vertical component of the wave's electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modelled as a good electrical conductor.

Question: What is the refractive index of the ground?


Answer: reflection

Question: When is polarized radiation reversed?


Answer: n=1

Question: What is the refractive index of air?


Answer: electrical conductor

Question: Besides a ground, what has these phases apply well to?


Answer: Fresnel coefficients

Context: When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave's power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave's angle of incidence and polarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.

Question: Who proposed this theory?


Answer: 180° out of phase

Question: Is the ground has a great conductor, how much of the wave will be reflected?


Answer: electromagnetic wave

Question: what is reflected and transmitted into the ground when a plane surface is struck?


Answer: power remaining

Question: What depends on the polarization and waves angle?


Answer: aperture

Context: The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which it delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has a flux of 1 pW / m2 (10−12 watts per square meter) and an antenna has an effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts rms at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.

Question: What is the portion of something that is reached by the radio transmission called?


Answer: direction

Question: What effects the function of signals received by an antenna?


Answer: microvolts

Question: What is a measure of the power of an antenna?


Answer: 12 pW of RF power

Question: How much power will be delivered to the reciever if the antenna has an effective area of 12 m/2?


Answer: Q

Context: The bandwidth characteristics of a resonant antenna element can be characterized according to its Q, just as one uses to characterize the sharpness of an L-C resonant circuit. However it is often assumed that there is an advantage in an antenna having a high Q. After all, Q is short for "quality factor" and a low Q typically signifies excessive loss (due to unwanted resistance) in a resonant L-C circuit. However this understanding does not apply to resonant antennas where the resistance involved is the radiation resistance, a desired quantity which removes energy from the resonant element in order to radiate it (the purpose of an antenna, after all!). The Q is a measure of the ratio of reactance to resistance, so with a fixed radiation resistance (an element's radiation resistance is almost independent of its diameter) a greater reactance off-resonance corresponds to the poorer bandwidth of a very thin conductor. The Q of such a narrowband antenna can be as high as 15. On the other hand, a thick element presents less reactance at an off-resonant frequency, and consequently a Q as low as 5. These two antennas will perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as the "hi-Q" antenna consisting of a thin conductor.

Question: The properties of a usable radio frequency can be called its?


Answer: Q

Question: What is a measure of the comparison between reactance and resistance?


Answer: 15

Question: What is the largest Q that could be achieved with a slimmer band antenna?


Answer: thick

Question: What type of element would be used to encounter less reactance?


Answer: loading coil

Context: For example, at 30 MHz (10 m wavelength) a true resonant 1⁄4-wavelength monopole would be almost 2.5 meters long, and using an antenna only 1.5 meters tall would require the addition of a loading coil. Then it may be said that the coil has lengthened the antenna to achieve an electrical length of 2.5 meters. However, the resulting resistive impedance achieved will be quite a bit lower than the impedance of a resonant monopole, likely requiring further impedance matching. In addition to a lower radiation resistance, the reactance becomes higher as the antenna size is reduced, and the resonant circuit formed by the antenna and the tuning coil has a Q factor that rises and eventually causes the bandwidth of the antenna to be inadequate for the signal being transmitted. This is the major factor that sets the size of antennas at 1 MHz and lower frequencies.

Question: What can be added to allow for an antenna shorter than the needed height to produce desired results?


Answer: lower

Question: How would the resistive impedance from this scenario compare to if the antenna was the proper height?


Answer: 2.5 meters

Question: The coil has lengthed the antenna to reach how much length electrically?


Answer: reactance

Question: What is the major thing that sets the size of antennas at lower frequencies?


Answer: 50 cm

Context: Consider a half-wave dipole designed to work with signals 1 m wavelength, meaning the antenna would be approximately 50 cm across. If the element has a length-to-diameter ratio of 1000, it will have an inherent resistance of about 63 ohms. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal loss. Feeding that antenna with a current of 1 ampere will require 63 volts of RF, and the antenna will radiate 63 watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the reflected current would arrive at the feed out-of-phase with the signal, causing the net current to drop while the voltage remains the same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency.

Question: How big would an antenna be used to with with one m wavelengths?


Answer: changing the matching system

Question: How could the rection of output be adressed by?


Answer: ampere

Question: What unit is used to measure current?


Answer: reducing output

Question: What effect occurs when the signal is reflected back into the antenna?


Answer: electrical

Context: Recall that a current will reflect when there are changes in the electrical properties of the material. In order to efficiently send the signal into the transmission line, it is important that the transmission line has the same impedance as the elements, otherwise some of the signal will be reflected back into the antenna. This leads to the concept of impedance matching, the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching between antennas and transmission lines is commonly handled through the use of a balun, although other solutions are also used in certain roles. An important measure of this basic concept is the standing wave ratio, which measures the magnitude of the reflected signal.

Question: What sort of changes in material would a current reflect?


Answer: impedance

Question: What must match between the transmission line and elements?


Answer: Impedance matching

Question: What technique is used to prevent unintentional decrease in signal?


Answer: balun

Question: How is this process usually used for transmission lines and antennas?


Answer: selectively delay

Context: An electromagnetic wave refractor in some aperture antennas is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.

Question: What is used to allow one to control the function of wave fronts moving through an antenna?


Answer: refractor

Question: What changes the structuak traits of a wave on either side?


Answer: spatial characteristics

Question: What is the main purpose of a refractor?


Answer: optical lens

Question: A refractor can be compared to what type of viewing?


Answer: actual antenna

Context: The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna's impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna's proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna's height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna's impedance.

Question: What can receive a stron signal by transmitting an original wave?


Answer: antenna element

Question: Where will the additional current be induced?


Answer: antenna's impedance

Question: What is altered because of the proximity to the ground?


Answer: reduced power

Question: what happens to the reflected wave which allows the antenna to reach its asympotic feedpoint impedance?


Answer: horizontal propagation

Context: For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by tne direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ=0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5λ. As the antenna height is increased, the number of lobes increases as well.

Question: What is between recieving and transmitting antenna's?


Answer: polarized vertically

Question: When is the emission at maximized recieved signal?


Answer: image at right

Question: Where is the radiation patterns in the vertical plane shown?


Answer: lobes

Question: What is also increased along with the antenna's height?


Answer: analog

Context: On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the p polarization (horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.

Question: What is another name for classical television transmissions?


Answer: multipath propagation

Question: Buildings can create ghost images because of what?


Answer: horizontal polarization

Question: When is ghosting reduced?


Answer: Vertically polarized analog television

Question: What cause less problems in digital terrestrial television?


Answer: antenna arrays

Context: Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However, because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.

Question: Where are the indiviual array elements known?


Answer: Current circulating

Question: What induces a feedpoint to antennas nearby?


Answer: electrical behaviour

Question: What are the mathmatic useful towards?


Answer: proximity

Question: What cause mutual interactions between the elements electric and magnetic fields?


Answer: open circuited

Context: This is a consequence of Lorentz reciprocity. For an antenna element not connected to anything (open circuited) one can write . But for an element which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding . This is the case, for instance, with the so-called parasitic elements of a Yagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint. Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.

Question: a antenna element not connected to anything is circuited how?


Answer: short circuited

Question: When is the element not allowed voltage?


Answer: Parasitic

Question: What element absorbs and reradiate RF-energy?


Answer: Yagi-Uda

Question: What antenna can the solid rod be viewed as a dipole antenna?


Answer: feedpoint

Question: Where can this solid rod be viewed?


Answer: broadcasting

Context: The difference in the above factors for the case of θ=0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base station antennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.

Question: What type of programmin relies on vertical polarization?


Answer: cancellation

Question: If you were to position your receiver closer to the ground what might be a negative of this placement?


Answer: mobile phones

Question: What is one use that would require an antenna to receive signals in various ways at once?


Answer: circular polarization.

Question: If you were to develop a signal to be used with mobile phones what would be an effective antenna type?


Answer: mixed polarization

Question: What would the antenna you are using take advantage of to allow it to work in multiple locations?


Answer: Loop antennas

Context: Loop antennas consist of a loop or coil of wire. Loops with circumference of a wavelength or larger act similarly to dipole antennas. However loops small in comparison to a wavelength act differently. They interact with the magnetic field of the radio wave instead of the electric field as other antennas do, and so are relatively insensitive to nearby electrical noise. However they have low radiation resistance, and so are inefficient for transmitting. They are used as receiving antennas at low frequencies, and also as direction finding antennas.

Question: What type of antenna can be formed by a circular segment of wire?


Answer: circumference of a wavelength

Question: What is a loop antenna compared with to determine its beahvior?


Answer: loops small

Question: If you needed to place an antenna somewhere with a large amount of interference, which type would be best?


Answer: low radiation resistance

Question: Why would this type be good for receiving but not transmtting?


Answer: direction finding

Question: What else would be an effective application of this antenna type?


Answer: the same

Context: It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving. For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.

Question: Are essential properties of an antenna changed based on what fungtion they are performing


Answer: reciprocity theorem of electromagnetics

Question: What proposition explains the equivalency of the recieving pattern of an antenna?


Answer: either transmitting or receiving

Question: Can the antenna serve more than one fungtion at a time?


Answer: radiation pattern

Question: What is one electrical trait of an antenna?


Answer: angiosperms

Context: The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with about 350,000 species. Like gymnosperms, angiosperms are seed-producing plants; they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term "angiosperm" comes from the Greek composite word (angeion-, "case" or "casing", and sperma, "seed") meaning "enclosed seeds", after the enclosed condition of the seeds.

Question: What are the most diverse group of land plants?


Answer: 350,000

Question: How many species of flowering plants are there about?


Answer: an enclosure

Question: What does an angiosperm produce its seeds within?


Answer: seed-producing plants

Question: What do angiosperms have in common with gymnosperms?


Answer: angeion

Question: What is the Greek word for "case" or "casing"?


Answer: at least 475 million years

Context: Fossilized spores suggest that higher plants (embryophytes) have lived on land for at least 475 million years. Early land plants reproduced sexually with flagellated, swimming sperm, like the green algae from which they evolved. An adaptation to terrestrialization was the development of upright meiosporangia for dispersal by spores to new habitats. This feature is lacking in the descendants of their nearest algal relatives, the Charophycean green algae. A later terrestrial adaptation took place with retention of the delicate, avascular sexual stage, the gametophyte, within the tissues of the vascular sporophyte. This occurred by spore germination within sporangia rather than spore release, as in non-seed plants. A current example of how this might have happened can be seen in the precocious spore germination in Selaginella, the spike-moss. The result for the ancestors of angiosperms was enclosing them in a case, the seed. The first seed bearing plants, like the ginkgo, and conifers (such as pines and firs), did not produce flowers. The pollen grains (males) of Ginkgo and cycads produce a pair of flagellated, mobile sperm cells that "swim" down the developing pollen tube to the female and her eggs.

Question: How long have higher plants lived on land?


Answer: with flagellated, swimming sperm

Question: How did early plants reproduce sexually?


Answer: spores

Question: Upright meisporangia allowed what to be dispersed to new habitats?


Answer: Charophycean green algae

Question: What are the nearest algal relatives existing today?


Answer: the spike-moss

Question: What is the common name for Selaginella?


Answer: abominable mystery

Context: The apparently sudden appearance of nearly modern flowers in the fossil record initially posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. However, the fossil record has considerably grown since the time of Darwin, and recently discovered angiosperm fossils such as Archaefructus, along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. Several groups of extinct gymnosperms, in particular seed ferns, have been proposed as the ancestors of flowering plants, but there is no continuous fossil evidence showing exactly how flowers evolved. Some older fossils, such as the upper Triassic Sanmiguelia, have been suggested. Based on current evidence, some propose that the ancestors of the angiosperms diverged from an unknown group of gymnosperms in the Triassic period (245–202 million years ago). Fossil angiosperm-like pollen from the Middle Triassic (247.2–242.0 Ma) suggests an older date for their origin. A close relationship between angiosperms and gnetophytes, proposed on the basis of morphological evidence, has more recently been disputed on the basis of molecular evidence that suggest gnetophytes are instead more closely related to other gymnosperms.[citation needed]

Question: What did Charles Darwin call the sudden appearance of nearly modern flowers in the fossil record?


Answer: angiosperm

Question: What type of fossil is the recently discovered Archaefructus?


Answer: evidence showing exactly how flowers evolved

Question: What fossil evidence is lacking when it comes to flowers?


Answer: Middle Triassic

Question: From what period does fossilized pollen suggest an older date for angiosperm origin?


Answer: relationship between angiosperms and gnetophytes

Question: What relationship proposed on the basis of morphological evidence has recently been disputed?


Answer: two

Context: The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at 319 million years ago and 192 million years ago. Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda, and directly addresses Darwin's "abominable mystery."

Question: How many distinct rounds of genome duplication events are suspected in the evolution of seed plants?


Answer: 319 million years ago

Question: When did the first whole genome duplication event occur?


Answer: whole genome duplication

Question: What type of event perhaps created the line which led to modern flowering plants?


Answer: by sequencing the genome of an ancient flowering plant

Question: How are duplication events studied?


Answer: Darwin

Question: Who coined the term "abominable mystery"?


Answer: about 125 million years BP

Context: The earliest known macrofossil confidently identified as an angiosperm, Archaefructus liaoningensis, is dated to about 125 million years BP (the Cretaceous period), whereas pollen considered to be of angiosperm origin takes the fossil record back to about 130 million years BP. However, one study has suggested that the early-middle Jurassic plant Schmeissneria, traditionally considered a type of ginkgo, may be the earliest known angiosperm, or at least a close relative. In addition, circumstantial chemical evidence has been found for the existence of angiosperms as early as 250 million years ago. Oleanane, a secondary metabolite produced by many flowering plants, has been found in Permian deposits of that age together with fossils of gigantopterids. Gigantopterids are a group of extinct seed plants that share many morphological traits with flowering plants, although they are not known to have been flowering plants themselves.

Question: When is the earliest known macrofossil identified as an angiosperm dated?


Answer: Archaefructus liaoningensis

Question: What is the earliest known angiosperm?


Answer: pollen

Question: What pushes the age of angiosperm 5 million years further back?


Answer: 250 million years ago

Question: How long ago has circumstantial evidence has been found for the existence of angiosperms?


Answer: Gigantopterids

Question: What group of now extinct seed plants had many of the traits of what are now flowering plants?


Answer: approximately 100 million years ago

Context: The great angiosperm radiation, when a great diversity of angiosperms appears in the fossil record, occurred in the mid-Cretaceous (approximately 100 million years ago). However, a study in 2007 estimated that the division of the five most recent (the genus Ceratophyllum, the family Chloranthaceae, the eudicots, the magnoliids, and the monocots) of the eight main groups occurred around 140 million years ago. By the late Cretaceous, angiosperms appear to have dominated environments formerly occupied by ferns and cycadophytes, but large canopy-forming trees replaced conifers as the dominant trees only close to the end of the Cretaceous 66 million years ago or even later, at the beginning of the Tertiary. The radiation of herbaceous angiosperms occurred much later. Yet, many fossil plants recognizable as belonging to modern families (including beech, oak, maple, and magnolia) had already appeared by the late Cretaceous.

Question: When does a great diversity of angiosperms appear in the fossil record?


Answer: great angiosperm radiation,

Question: What is the appearance of a large amount of angiosperms in the fossil record known as?


Answer: 40 million years ago

Question: When did the division of the eight main groups of angiosperms occur?


Answer: dominated environments

Question: What were the angiosperms up to by the late Cretaceous?


Answer: Cretaceous

Question: Beech and maple had already appeared by what period?


Answer: Island genetics

Context: Island genetics provides one proposed explanation for the sudden, fully developed appearance of flowering plants. Island genetics is believed to be a common source of speciation in general, especially when it comes to radical adaptations that seem to have required inferior transitional forms. Flowering plants may have evolved in an isolated setting like an island or island chain, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp, for example). Such a relationship, with a hypothetical wasp carrying pollen from one plant to another much the way fig wasps do today, could result in the development of a high degree of specialization in both the plant(s) and their partners. Note that the wasp example is not incidental; bees, which, it is postulated, evolved specifically due to mutualistic plant relationships, are descended from wasps.

Question: What is one proposed explanation for the instant appearance of flowering plants?


Answer: speciation

Question: What is island genetics thought to be a default source of?


Answer: inferior transitional forms

Question: What did radical adaptations seem to have required?


Answer: highly specialized relationship with some specific animal

Question: How did an isolated setting like an island help flowering plants evolve?


Answer: wasps

Question: What are bees descended from?


Answer: distribution of seeds

Context: Animals are also involved in the distribution of seeds. Fruit, which is formed by the enlargement of flower parts, is frequently a seed-dispersal tool that attracts animals to eat or otherwise disturb it, incidentally scattering the seeds it contains (see frugivory). Although many such mutualistic relationships remain too fragile to survive competition and to spread widely, flowering proved to be an unusually effective means of reproduction, spreading (whatever its origin) to become the dominant form of land plant life.

Question: What are animals also a part of?


Answer: Fruit

Question: What did the enlargement of flower parts evolve to form?


Answer: seed-dispersal

Question: What does a plant get out of forming fruit?


Answer: fragile

Question: What are many mutualistic relationships, thus failing to survive competition?


Answer: flowering

Question: What turned out to be unusually effective for plants to reproduce?


Answer: Flower ontogeny

Context: Flower ontogeny uses a combination of genes normally responsible for forming new shoots. The most primitive flowers probably had a variable number of flower parts, often separate from (but in contact with) each other. The flowers tended to grow in a spiral pattern, to be bisexual (in plants, this means both male and female parts on the same flower), and to be dominated by the ovary (female part). As flowers evolved, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant or at least "ovary-inferior".

Question: What uses a combination of genes to form new shoots?


Answer: separate from (but in contact with) each other

Question: What were plant parts like in their primitive days?


Answer: grow in a spiral pattern

Question: How did flowers become bixsexual?


Answer: fused together

Question: What did some plant parts do as they evolved?


Answer: "ovary-inferior"

Question: What is a term for a plant with a specific sex per flower?


Answer: present day

Context: Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that some of them cannot be pollinated in nature. Many modern domesticated flower species were formerly simple weeds, which sprouted only when the ground was disturbed. Some of them tended to grow with human crops, perhaps already having symbiotic companion plant relationships with them, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection.

Question: How long has flower evolution occurred?


Answer: formerly simple weeds

Question: What heritage do many modern domesticated flower species have?


Answer: pollinated

Question: Humans have effected some flowers so much they can no longer do what in nature?


Answer: symbiotic companion plant relationships

Question: Why did weeds grow with human crops?


Answer: prettiest

Question: What feature helped flowers not get plucked?


Answer: Amborellales, Nymphaeales, and Austrobaileyales

Context: The exact relationship between these eight groups is not yet clear, although there is agreement that the first three groups to diverge from the ancestral angiosperm were Amborellales, Nymphaeales, and Austrobaileyales. The term basal angiosperms refers to these three groups. Among the rest, the relationship between the three broadest of these groups (magnoliids, monocots, and eudicots) remains unclear. Some analyses make the magnoliids the first to diverge, others the monocots. Ceratophyllum seems to group with the eudicots rather than with the monocots.

Question: What three groups were the first to diverge from angiosperm?


Answer: basal

Question: What term refers to the first three groups to diverge from angiosperm?


Answer: unclear

Question: How clear is the relationship between the broadest of the three non-basal angiosperm groups?


Answer: magnoliids

Question: What group do some analyses seem to indicate diverged first?


Answer: Angiosperm

Context: The botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon (bottle, vessel) and σπέρμα, (seed), was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked. The term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any approach to its modern scope became possible only after 1827, when Robert Brown established the existence of truly naked ovules in the Cycadeae and Coniferae, and applied to them the name Gymnosperms.[citation needed] From that time onward, as long as these Gymnosperms were, as was usual, reckoned as dicotyledonous flowering plants, the term Angiosperm was used antithetically by botanical writers, with varying scope, as a group-name for other dicotyledonous plants.

Question: What term did Paul Hermann come up with in 1690?


Answer: primary

Question: What did Hermann use the term angiosperm a primary division of in the plant kingdom?


Answer: Carl Linnaeus

Question: Who restricted the application of the angiosperm term?


Answer: naked ovules

Question: What did Robert Brown establish the existence of in Cycadeae and Coniferae?


Answer: other dicotyledonous plants

Question: What is the group-name angiosperm has been used for by botanical writers?


Answer: coherent

Context: In most taxonomies, the flowering plants are treated as a coherent group. The most popular descriptive name has been Angiospermae (Angiosperms), with Anthophyta ("flowering plants") a second choice. These names are not linked to any rank. The Wettstein system and the Engler system use the name Angiospermae, at the assigned rank of subdivision. The Reveal system treated flowering plants as subdivision Magnoliophytina (Frohne & U. Jensen ex Reveal, Phytologia 79: 70 1996), but later split it to Magnoliopsida, Liliopsida, and Rosopsida. The Takhtajan system and Cronquist system treat this group at the rank of division, leading to the name Magnoliophyta (from the family name Magnoliaceae). The Dahlgren system and Thorne system (1992) treat this group at the rank of class, leading to the name Magnoliopsida. The APG system of 1998, and the later 2003 and 2009 revisions, treat the flowering plants as a clade called angiosperms without a formal botanical name. However, a formal classification was published alongside the 2009 revision in which the flowering plants form the Subclass Magnoliidae.

Question: In taxonomies, what type of group are flowering plants treated?


Answer: flowering plants

Question: What does anthophyta mean?


Answer: Angiospermae

Question: What do the Wettstein and Engler systems use at the assigned rank of subdivision?


Answer: a clade called angiosperms

Question: How does the APG system of 1998, with its 2003 and 2009 revisions, treat flowering plants?


Answer: Magnoliidae

Question: What formal subclass classification were flowering plants given in 2009?


Answer: how the flowering plants should be arranged

Context: The internal classification of this group has undergone considerable revision. The Cronquist system, proposed by Arthur Cronquist in 1968 and published in its full form in 1981, is still widely used but is no longer believed to accurately reflect phylogeny. A consensus about how the flowering plants should be arranged has recently begun to emerge through the work of the Angiosperm Phylogeny Group (APG), which published an influential reclassification of the angiosperms in 1998. Updates incorporating more recent research were published as APG II in 2003 and as APG III in 2009.

Question: What consensus is the AGP trying to reach?


Answer: classification

Question: What internal component has undergone considerable revision?


Answer: The Cronquist system

Question: What system did Arthur Cronquist put forth in 1968, but not publish in full form until 1981?


Answer: APG

Question: Who published an influential reclassification of the angiosperms in 1998?


Answer: monophyletic

Context: Recent studies, as by the APG, show that the monocots form a monophyletic group (clade) but that the dicots do not (they are paraphyletic). Nevertheless, the majority of dicot species do form a monophyletic group, called the eudicots or tricolpates. Of the remaining dicot species, most belong to a third major clade known as the magnoliids, containing about 9,000 species. The rest include a paraphyletic grouping of primitive species known collectively as the basal angiosperms, plus the families Ceratophyllaceae and Chloranthaceae.

Question: What type of groups do monocots form, based on a recent APG studies?


Answer: dicot

Question: Eudicots or tricolpates are part of a monophyletic group formed by what species?


Answer: magnoliids

Question: What third major clade can many dicot species be found in?


Answer: about 9,000

Question: How many species dicot species are magnoliids?


Answer: paraphyletic

Question: Basal angiosperms are what type of grouping of primitive species?


Answer: 250,000 to 400,000

Context: The number of species of flowering plants is estimated to be in the range of 250,000 to 400,000. This compares to around 12,000 species of moss or 11,000 species of pteridophytes, showing that the flowering plants are much more diverse. The number of families in APG (1998) was 462. In APG II (2003) it is not settled; at maximum it is 457, but within this number there are 55 optional segregates, so that the minimum number of families in this system is 402. In APG III (2009) there are 415 families.

Question: What is the estimated range for the number of flowering plants?


Answer: 12,000

Question: How many species of moss is there?


Answer: diverse

Question: What does the large number of flowering plant species indicate is true of them in general?


Answer: 402

Question: What are the minimum number of families in the APG system?


Answer: 415

Question: How many families are in AGP III?


Answer: an open ring

Context: In the dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles (interfascicular cambium), a complete ring is formed, and a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside. The soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.

Question: What shape are the bundles in the young stem of dicotyledons arranged in?


Answer: xylem and phloem

Question: What does the cambium separate?


Answer: cambium

Question: What is a layer of meristem or formative tissue known as?


Answer: increase in thickness

Question: What results from the development of xylem on the inside and phloem on the outside?


Answer: annual rings

Question: What's another name for the concentric rings in trees?


Answer: flower

Context: The characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species. The function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally on a shoot or from the axil of a leaf (where the petiole attaches to the stem). Occasionally, as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More typically, the flower-bearing portion of the plant is sharply distinguished from the foliage-bearing or vegetative portion, and forms a more or less elaborate branch-system called an inflorescence.

Question: What is the defining feature of angiosperms?


Answer: form and elaboration

Question: What characteristic flowers show variation in?


Answer: establishing relationships among angiosperm species

Question: What do flowers provide the best external feature for doing?


Answer: the ovule

Question: What is it the function of the flower to ensure fertilization of?


Answer: inflorescence

Question: What is the name of a branch system?