An antenna is a key component of a wireless link which efficiently couples electromagnetic energy from the transmitter to free space and from free space to the receiver. An antenna is generally a bidirectional device, i.e, the power through the antenna can flow in both the directions, hence it works as a transmitting as well as a receiving antenna. An antenna acts as an interface between the radiated electromagnetic waves and the guided waves. It can be thought of as a mode transformer which transforms a guided wave field distribution into a radiated-wave field distribution.
The angular distribution of the transmitted power around the antenna is generally known as :
Radiation pattern
The standard term is the radiation pattern. It is defined as a graphical representation of the antenna's radiation properties as a function of direction — that is, how the radiated power is distributed over the angular coordinates θ and φ at a fixed large distance. That is exactly what the question describes, so the answer is option 3.
Why option 2 is the near miss. "Power pattern" is a genuine term, but it is a subdivision of the radiation pattern rather than the general name. A radiation pattern may be plotted in several forms:
| Form | Quantity plotted |
|---|---|
| Field pattern | \(|E(\theta,\phi)|\) |
| Power pattern | \(|E(\theta,\phi)|^{2}\), usually in dB |
| Phase pattern | the phase of the field |
The question asks for what the distribution is "generally known as", and the general, umbrella term is radiation pattern. Note also that a 3 dB drop in the power pattern corresponds to a 0.707 drop in the field pattern — the same angular width, read on different scales.
Why the other two fail. "Angular pattern" is not standard terminology at all. An antenna array is a physical arrangement of several radiating elements, not a description of the radiated power — though it is one way of shaping a pattern.
The features a radiation pattern displays.
The main lobe contains the direction of maximum radiation; side lobes are the smaller maxima either side of it; the back lobe points opposite the main beam; and nulls are the directions of zero radiation.
The numbers read off it are the half-power beamwidth (HPBW), the beamwidth between first nulls (BWFN), the side-lobe level and the front-to-back ratio.
Where the pattern must be measured. Only in the far field, beyond
\(R \gt \dfrac{2D^{2}}{\lambda}\)
because closer in the relative phases of the contributions from different parts of the aperture are still changing with distance and the pattern has not settled into its final shape.
Reciprocity, which the passage itself notes. Because an antenna is bidirectional, its receiving pattern is identical to its transmitting pattern — so a single measurement serves both roles.
Hence, the angular distribution of transmitted power is the radiation pattern.
Similar Questions
An antenna is polarized in the plane of the field perpendicular to
The value of radiation resistance of a Hertzian dipole of length \(\dfrac{\lambda}{80}\) is given by
An antenna is generally a metallic object, often a wire or collection of wires, used to convert high frequency current into electromagnetic waves and vice-versa. Antenna serve either or both of the following two functions, generation or the collection of electromagnetic energy. In a transmitting system, a radio-frequency signal is developed, amplified, modulated and applied to the antenna. The R-F currents flowing through the antenna produce electromagnetic waves which radiate into the atmosphere. In a receiving system, electromagnetic waves "cutting" through the antenna induce alternating currents for use by the receiver.
Efficient operation also requires that the receiving antenna be of the same polarization as the transmitting antenna. Polarization is the direction of the electric field and is therefore, the same as the antennas physical configuration. Thus vertical antenna will transmit vertical polarized light, any antenna having a physical length that is one-half wavelength of the applied frequency is called a Hertz antenna. Hertz antenna are predominantly used with frequencies above 2 MHz. Usually, at frequencies below 2 MHz, a Marconi type of antenna is used. The Marconi antenna is usually a quarter-wave grounded antenna or any odd multiple of a quarter wavelength.
The Yagi-Uda antenna consists of a drivers element and two or more parasitic elements. Yagi-Uda has two parasitic elements, a reflector and a director. This Yagi-Uda antenna provides about 7 dB of power gain with respect to a half-wavelength dipole reference. More complex antennas may be circularly polarized both vertically and horizontally polarized waves are radiated with equal power in both. If the powers are unequal the antenna is said to be elliptically polarized.
A horn is an ideal antenna for terminating a waveguide and may be conical, rectangular or sectorial. Wide band antennas either when the transmissions are wide band or when working of narrow channels over a wide frequency range is the major application. Helical antenna, which consists of a loosely wound helix backed up by a metal ground plane. Loop antennas are often used for direction finding. Loops have many shapes and generally consists of a single turn of wire. Discone is a ground plane antenna evolved from the vertical dipole and having a very similar radiation pattern.
For a half wave dipole the directivity ‘D’ in dB is of the order of :
Important Questions from Basics of Antenna
Arrange the following antennas in ascending order of their radiation resistance.
A. Short dipole (L = \(\frac{\lambda}{10}\) )(I av = l o)
B. Short dipole (L= \(\frac{\lambda}{10}\) )( I av = l o/2)
C. Linear \(\frac{\lambda}{2}\) dipole (sinusoidal current distribution)
D. Small Loop (square loop) single turn of(L = \(\frac{\lambda}{10}\) )
Choose the correct answer from the options given below
If the frequency of the signal is 1 MHz, the minimum height of the transmitting antenna should be:
The Antenna employed in Television receivers
Which of the following is NOT true with respect to antennas?
An instrument to check whether RF power in the transmission line is transferred to the antenna is:
