GATE ECE 2020 | Antennas Question 3 | Electromagnetics

GATE ECE 2020

MCQ (Single Correct Answer)

-0.67

For an infinitesimally small dipole in free space, the electric field $E_\theta$ in the far field is proportional to $\frac{e^{-j k r}}{r} \sin \theta$, where $k=\frac{2 \pi}{\lambda}$. A vertical infinitesimally small electric dipole ( $\delta l \ll \lambda$ ) is placed at a distance $h(h>0)$ above an infinite ideal conducting plane, as shown in the figure. The minimum value of $h$, for which one of the maxima in the far field radiation pattern occurs at $\theta=60^{\circ}$, is

GATE ECE 2020 Electromagnetics - Antennas Question 2 English

$0.75 \lambda$

$0.25 \lambda$

$0.5 \lambda$

$\lambda$

GATE ECE 2017 Set 1

MCQ (Single Correct Answer)

-0.6

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 radiation pattern for $$0 \le \phi \le \pi $$. Here the angle $$\theta \left( {0 \le \theta \le \pi } \right)$$ is measured from the z-axis, and the angle $$\phi \left( {0 \le \phi \le 2\pi } \right)$$ is measured from the x-axis in the x-y plane.

$$\theta = {90^ \circ },\,\,\,\phi = {45^ \circ }$$

$$\theta = {45^ \circ },\,\,\,\phi = {90^ \circ }$$

$$\theta = {90^ \circ },\,\,\,\phi = {135^ \circ }$$

$$\theta = {45^ \circ },\,\,\,\phi = {135^ \circ }$$

GATE ECE 2016 Set 1

MCQ (Single Correct Answer)

-0.6

The far-zone power density radiated by a helical antenna is approximated as: $$$\overrightarrow W {\,_{rad}} = \overrightarrow W \,average\, \approx \,\widehat a{}_rC{}_0\,{1 \over {{r^2}}}{\cos ^4}\theta $$$

The radiated power density is symmetrical with respect to $$\phi $$ and exists only in the upper hemisphere: $$0 \le \theta \le {\pi \over 2};\,\,\,\,0 \le \theta \le 2\pi ;$$

$${C_0}$$ is a constant. The power radiated by the antenna (in watts) and the maximum directivity of the antenna, respectively, are

$$1.5{C_0},\,\,10dB$$

$$1.256{C_0},\,\,10dB$$

$$1.256{C_0},\,\,12dB$$

$$1.5{C_0},\,\,12dB$$

GATE ECE 2016 Set 1

MCQ (Single Correct Answer)

-0.6

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-amplifier that has a noise figure of 2 dB and an available gain of 40 dB over an effective bandwidth of $$12$$ $$MHz$$. The effective input noise temperature $${T_e}$$ for the amplifier and the noise power $${P_{ao}}$$ at the output of the preamplifier, respectively, are

$${T_e} = 169.36K$$ and $${P_{ao}} = 3.73 \times {10^{ - 10}}\,\,\,W$$

$${T_e} = 170.8K$$ and $${P_{ao}} = 4.56 \times {10^{ - 10}}\,\,\,W$$

$${T_e} = 182.5K$$ and $${P_{ao}} = 3.85 \times {10^{ - 10}}\,\,\,W$$

$${T_e} = 160.62K$$ and $${P_{ao}} = 4.6 \times {10^{ - 10}}\,\,\,W$$