1

GATE ECE 1996

Subjective

+5

-0

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 $${{\rm I}_0}\,\angle \alpha $$ respectively. What should be the value of $$\alpha $$ so that the radiation pattern has a null at $$\theta = {30^ \circ }$$. Find the direction of the maximum radiation for that value of $$\alpha $$ and draw the radiation pattern. ($$\lambda \,\,$$ is the wavelength of operation)

2

GATE ECE 1995

Subjective

+5

-0

Two dipoles are so fed and oriented in free space that they produce the following electromagnetic waves:
$$${E_x} = 10\,{e^{j\left( {\omega t - z\pi /3} \right)}}\,\,volts/metre$$$
$$${E_y} = j\,\,10\,{e^{j\left( {\omega t - z\pi /3} \right)}}\,\,volts/metre$$$

(a) Write down the expression for the corresponding magnetic field strength vector.

(b) Calculate the frequency of the wave.

(C) Give the complete description of the polarization of the wave.

3

GATE ECE 1994

Subjective

+5

-0

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 aperture efficiency of 64%. If the space crafts A's receiver requires 1pW for a 20 dB signal-to-noise ratio, what transmitter power is required on the spacecraft B to achieve this signal-to-noise ratio?

4

GATE ECE 1993

Subjective

+5

-0

Consider an array of two non-directional radiators with spacing $$d\,\, = \,\,0.5\,\,\lambda $$. Determine the directions of maximum radiation when the radiators are excited as shown in Fig.. Calculate the phase shift required for turning the direction of the maximum radiation by $${90^ \circ }$$ keeping the separation d unchanged.

Questions Asked from Antennas (Marks 5)

Number in Brackets after Paper Indicates No. of Questions

GATE ECE Subjects

Network Theory

Control Systems

Electronic Devices and VLSI

Analog Circuits

Digital Circuits

Microprocessors

Signals and Systems

Representation of Continuous Time Signal Fourier Series Discrete Time Signal Fourier Series Fourier Transform Discrete Time Signal Z Transform Continuous Time Linear Invariant System Transmission of Signal Through Continuous Time LTI Systems Discrete Time Linear Time Invariant Systems Sampling Continuous Time Signal Laplace Transform Discrete Fourier Transform and Fast Fourier Transform Transmission of Signal Through Discrete Time Lti Systems Miscellaneous Fourier Transform

Communications

Electromagnetics

General Aptitude