rajpurkar/squad huggingface dataset:
Title: Antenna_(radio)

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: half-wave dipole

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

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

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

Question: What popular type combines more that one antenna?
Answer: folded dipole
Title: Antenna_(radio)

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: f0

Question: What can be added to f0 to create a standing wave pattern?
Answer: 3f0

Question: What multiple is essential for wavelengths?
Answer: 1⁄4

Question: How are waves which are used in the ways discussed controlled?
Answer: harmonically
Title: Antenna_(radio)

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: imitate

Question: What frequency develops a current peak?
Answer: resonant frequency

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

Question: What could be the best possible output versus input ratio?
Answer: lossless
Title: Antenna_(radio)

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: impedance matching

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

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

Question: What phrase describes the process of purposely using a lower standing antenna at a less than peak frequency?
Answer: electrical lengthening
Title: Antenna_(radio)

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: resonant multiples

Question: What is the most common application of resonant antennas?
Answer: single target signal

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

Question: For use with more than one channel changes are made to increase what property?
Answer: bandwidth
Title: Antenna_(radio)

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: inverse square law

Question:  How is the compactness of the signal measured?
Answer: Watts per square metre

Question: What type of project would call for more than one element used together?
Answer: higher performance
Title: Antenna_(radio)

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: feed point

Question: What part of the current is usually strongest?
Answer: center

Question: What does this result in?
Answer: standing wave pattern

Question: Element used to provide support to the original signal are called?
Answer: passive elements
Title: Antenna_(radio)

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: Yagi-Uda array

Question: Does this device improve the operation of the antenna?
Answer: does not contribute

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

Question: Adding more elements to a Yagi-Uda would have what effect?
Answer: increasingly directional
Title: Antenna_(radio)

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: active elements

Question: What is the most common element used to create a single in phase signal?
Answer: half-wave dipoles

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

Question: What is a more complicated occurrence of the single in-phase producing antenna?
Answer: log-periodic
Title: Antenna_(radio)

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: extended conductive surface

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

Question: What allowance can be made for gaps without loss of performance?
Answer: less than 1⁄10

Question: What is the most recognized type of an antenna that has its basis in reflection?
Answer: parabolic reflector
Title: Antenna_(radio)

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: a capacitor at the frequency of operation

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

Question: What is used in most AM broadcaster receivers?
Answer: loop

Question: When using a small loop antenna at a low frequency, what may occur?
Answer: impedance matching
Title: Antenna_(radio)

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: resistive impedance

Question: Where does cancellation of any reactance seen?
Answer: antenna terminals

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

Question: What is an antenna designed to have?
Answer: purely resistive feedpoint
Title: Antenna_(radio)

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: resonant

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

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

Question: What is lessened by the Yagi-Uda design?
Answer: directivity
Title: Antenna_(radio)

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: diameter

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

Question: What would be used to create a half wave or quarter wave dipole?
Answer: A long thin wire

Question: What type of tubes are generally used for sturdier always of antennas?
Answer: thick tubes
Title: Antenna_(radio)

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: widens

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

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

Question: What is an essential for dealing with directing the flow of power?
Answer: trap's
Title: Antenna_(radio)

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: gain

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

Question: What is the meaning of intensity?
Answer: power per unit surface area

Question: What type of an antenna would offer the same level of power to each possible destination?
Answer: isotropic
Title: Antenna_(radio)

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: longer range

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

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

Question: What type of antenna would be best if placement was tricky?
Answer: Low-gain
Title: Antenna_(radio)

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: proportional

Question: what could an antenna with complete electrical efficiency be said to have?
Answer: no loss

Question: Another term for the effective area is?
Answer: Aeff

Question: hat could an antenna with complete electrical efficiency be said to have?
Answer: 1
Title: Antenna_(radio)

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: relative field strength

Question: What type of pictoral aid is often used to show this?
Answer: three-dimensional graph

Question:  A sphere shows what type of antennas radiation?
Answer: isotropic

Question: Dipoles are considered to be what antenna type?
Answer: nondirectional

Question: What would an omnidirectional antenna look like if plotted?
Answer: donut
Title: Antenna_(radio)

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: nulls

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

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

Question: What is the main distinction of side lobes?
Answer: represent unwanted radiation