GATE Questions & Answers of Antennas: antenna types, radiation pattern, gain and directivity, return loss, antenna arrays

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Total 11 Questions have been asked from Antennas: antenna types, radiation pattern, gain and directivity, return loss, antenna arrays topic of Electromagnetics subject in previous GATE papers. Average marks 1.64.

Consider a wireless communication link between a transmitter and a receiver located in free space, with finite and strictly positive capacity. If the effective areas of the transmitter and the receiver antennas, and the distance between them are all doubled, and everything else remains unchanged, the maximum capacity of the wireless link

A half wavelength dipole is kept in the x-y plane and oriented along 45° from the x –axis. Determine the direction of null in the radiation pattern for $ 0\leq\mathrm\phi\leq\pi $, Here the angle $ \theta\left(0\leq\mathrm\theta\leq\pi\right) $ is measured from the z-axis, and the angle $ \mathrm\phi\left(0\leq\mathrm\phi\leq2\pi\right) $ is measured from the x-axis in the x-y plane.

Two lossless X-band horn antennas are separated by a distance of $200\lambda$. The amplitude reflection coefficients at the terminals of the transmitting and receiving antennas are 0.15 and 0.18, respectively. The maximum directivities of the transmitting and receiving antennas (over the isotropic antenna) are 18 dB and 22 dB, respectively. Assuming that the input power in the lossless transmission line connected to the antenna is 2 W, and that the antennas are perfectly aligned and polarization matched, the power ( in mW) delivered to the load at the receiver is ________

The far-zone power density radiated by a helical antenna is approximated as:

${\overrightarrow W}_{rad}={\overrightarrow W}_{average}\approx\widehat{a_r}C_0\frac1{r^2}\cos^4\theta$

The radiated power density is symmetrical with respect to $\phi$ and exists only in the upper hemisphere: $0\;\leq\;\theta\;\leq\frac\pi2;\;0\;\leq\;\phi\;\leq2\pi;\;C_0$is a constant. The power radiated by the antenna (in watts) and the maximum directivity of the antenna, respectively, are

A radar operating at 5 GHz uses a common antenna for transmission and reception. The antenna has a gain of 150 and is aligned for maximum directional radiation and reception to a target 1 km away having radar cross-section of 3 m2. If it transmits 100 kW, then the received power (in μW) is __________

Two half –wave dipole antennas placed as shown in the figure are excited with sinusoidally varying currents of frequency 3 MHz and phase shift of π/2 between them (the element at the origin leads in phase) . If the maximum radiated E –field at the point P in the x-y plane occurs at an azimuthal angle of 60o, the distance d (in meters) between the antennas is________.

The directivity of an antenna array can be increased by adding more antenna, as a larger number of elements

The radiation pattern of an antenna in spherical co-ordinates is given by


The directivity of the antenna is

For a Hertz dipole antenna, the half power beam width (HPBW) in the E-plane is

At 20 GHz, the gain of a parabolic dish antenna of 1 meter diameter and 70% efficiency is

A λ2 dipole is kept horizontally at a height of λ02 above a perfectly conducting infinite ground plane. The radiation pattern in the plane of the dipole (E plane) looks approximately as