GATE ECE
Electromagnetics
Antennas
Previous Years Questions

## Marks 1

The directivity of an antenna array can be increased by adding more antenna elements, as a larger number of elements
For an antenna radiating in free space, the electric field at a distance of 1 km is found to be 12 m V/m. Given that intrinsic impedance of the free s...
Match column A with column B. Column 1. Point electromagnetic source 2. Dish antenna 3. Yagi-Uda antenna Column P. Highly directional Q...
The radiation pattern of an antenna in spherical co-ordinates is given by $$F\,(\theta )\, = {\cos ^4}\,\theta \,\,\,;\,\,0\,\, \le \,\,\theta \,\, \... For a Hertz dipole antenna, the half power beam width (HPBW) in the E-plane is A transmission line is feeding 1 Watt of power to a horn antenna having gain of 10 dB. The antenna is matched to the transmission line. The total powe... Refractive index of glass is 1.5. Find the wavelength of a beam of light with a frequency of$${10^{14}}$$Hz in glass. Assume velocity of light is$$...
Consider a lossless antenna with a directive gain of + 6 dB. If 1 m W of power is fed to it the total power radiated by the antenna will be
The line-of-sight communication requires the transmit and receive antennas to face each other. If the transmit antenna is vertically polarized for bes...
If the diameter of a $$\lambda /2$$ dipole antenna is increased from $$\lambda /100$$ to $$\lambda /50$$ then is
An antenna in free space receives 2$$\mu$$ W of power when the incident electric field is 20 m V/m rms. The effective aperture of the antenna is
The radiation resistance of a circular loop of one turn is 0.01 $$\Omega$$. The radiation resistance of five turns of such a loop will be
The far field of an antenna varies with distance r as
The vector $$\mathop H\limits^ \to$$ in the far field of an antenna satisfiels
An antenna when radiating, has a highly directional radiation pattern. When the antenna is receiving its radiation pattern
For a dipole antenna

## Marks 2

A half wavelength dipole is kept in the x-y plane and oriented along $${45^ \circ }$$ from the x-axis. Determine the direction of null in the radiatio...
An antenna pointing in a certain direction has a noise temperature of $$50K$$. The ambient temperature is $$290K$$. The antenna is connected to a pre-...
Two lossless X-band horn antennas are separated by a distance of $$200\lambda$$. The amplitude reflection coefficients at the terminals of the transm...
The far-zone power density radiated by a helical antenna is approximated as: $$\overrightarrow W {\,_{rad}} = \overrightarrow W \,average\, \approx \... Two half-wave dipole antennas placed as shown in the figure are excited with sinusoidally varying currents of frequency 3 MHz and phase shift of$$\pi...
At 20 GHz, the gain of a parabolic dish antenna of 1 meter diameter and 70% efficiency is
A $$\lambda /2$$ dipole is kept horizontally at a height of $${\lambda _0}/2$$ above a perfectly conducting infinite ground plane. The radiation patte...
A mast antenna consisting of a 50 meter long vertical conductor operates over a perfectly conducting ground plane. It is base-fed at frequency of 600...
Two identical and parallel dipole antennas are kept apart by a distance $$\lambda /4$$ of in the H-plane. They are fed with equal currents but the rig...
Two identical antennas are placed in the $$\theta = \pi /2$$ plane as shown in figure. The elements have equal amplitude excitation with 180° polarit...
A person with a receiver is 5 Km away from the transmitter. What is the distance that this person must move further to detect a 3-dB decrease in signa...
In a uniform linear array, four isotropic radiating elements are spaced $$\lambda /4$$ apart. The progressive phase shift between the elements require...
A medium wave radio transmitter operating at a wavelength of 492 m has a tower antenna of height 124m. What is the radiation resistance of the antenna...
For an 8 feet (2.4 m) parabolic disk antenna operating at 4 GHz, the minimum distance required for far field measurement is closest to
The half-power beam widths (HPBW) of an antenna in the two orthogonal planes are $${100^ \circ }$$ and $${60^ \circ }$$ respectively. The directivity...
A transmitting antenna radiates 251 W isotropically. A receiving antenna, located 100m away from the transmitting antenna, has an effective aperture o...
A parabolic dish antenna has a conical beam 20 wide. The directivity of the antenna is approximately
A transverse electromagnetic wave with circular polarization is received by a dipole antenna. Due to polarization mismatch, the power transfer efficie...
A 1 km long microwave link uses two antennas each having 30dB gain. If the power transmitted by one antenna is 1 W at 3 GHz, the power received by the...
Two dissimilar antennas having their maximum directivities equal
The beam width-between-first-null of a uniform linear array of N equally-spaced (element spacing = d) equally-excited antennas is determined by
In a board side array of 20 isotropic radiators, equally spaced at a distance of $$\lambda /2$$, the veam width between first nulls is
Two isotropic antennas are separated by a distance of two wavelengths. If both the antennas are fed with currents of equal phase and magnitude, the nu...
In the case of ground wave propagation, at far-off distances from the transmitting tower antenna, the Poynting vector is
The electric field E and the magnetic field H of a short dipole antenna satisfy the condition

## Marks 4

A thin dipole antenna is $$\left( {\lambda /15} \right)$$ long, where $$\lambda$$ is the voperating wavelength. If the dipole has a loss resistance o...

## Marks 5

Consider a linear array of two half - wave dipoles A and B as shown in Fig. The dipoles are $${\lambda \over 4}$$ apart and are excited in such a way...
The average power of an omni-directional antenna varies as the magnitude of cos($$\theta$$) where $$\theta$$ is the azimuthal angle. Calculate the m...
A dipole antenna has a sin$$\theta$$ radiation pattern where the angle $$\theta$$ is measured from the axis of the dipole. The dipole is vertically ...
Two isotropic antennas A and B from an array as shown in Fig. The currents fed to the two antennas are $${{\rm I}_0}\,\angle 0$$ and $${{\rm I}_0}\,\a... Two dipoles are so fed and oriented in free space that they produce the following electromagnetic waves:$$\${E_x} = 10\,{e^{j\left( {\omega t - z\pi ...
Two spacecrafts are separated by 3000 km. Each has a paraboloidal reflector antenna of 0.85 m diameter operating at a frequency of 2 GHz with an apert...
Consider an array of two non-directional radiators with spacing $$d\,\, = \,\,0.5\,\,\lambda$$. Determine the directions of maximum radiation when th...

## Marks 8

Elements of a linear array of three equally spaced (element spacing $$0.5\lambda$$ ) vertical mast radiators are excited as given in Fig. For the hor...

## Marks 10

In the radiation pattern of a 3-element array of isotropic radiators equally spaced at distances of $${\lambda /4}$$ it is required to place a null a...
Two vertically oriented half wave dipoles are spaced 1.5 wavelengths apart to from an array. Calculate the half power beam widths of the major lobes o...
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