1
GATE ECE 2017 Set 1
MCQ (Single Correct Answer)
+2
-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.
A
$$\theta = {90^ \circ },\,\,\,\phi = {45^ \circ }$$
B
$$\theta = {45^ \circ },\,\,\,\phi = {90^ \circ }$$
C
$$\theta = {90^ \circ },\,\,\,\phi = {135^ \circ }$$
D
$$\theta = {45^ \circ },\,\,\,\phi = {135^ \circ }$$
2
GATE ECE 2016 Set 1
MCQ (Single Correct Answer)
+2
-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
A
$${T_e} = 169.36K$$ and $${P_{ao}} = 3.73 \times {10^{ - 10}}\,\,\,W$$
B
$${T_e} = 170.8K$$ and $${P_{ao}} = 4.56 \times {10^{ - 10}}\,\,\,W$$
C
$${T_e} = 182.5K$$ and $${P_{ao}} = 3.85 \times {10^{ - 10}}\,\,\,W$$
D
$${T_e} = 160.62K$$ and $${P_{ao}} = 4.6 \times {10^{ - 10}}\,\,\,W$$
3
GATE ECE 2016 Set 1
Numerical
+2
-0
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 ________ .
Your input ____
4
GATE ECE 2016 Set 1
MCQ (Single Correct Answer)
+2
-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

A
$$1.5{C_0},\,\,10dB$$
B
$$1.256{C_0},\,\,10dB$$
C
$$1.256{C_0},\,\,12dB$$
D
$$1.5{C_0},\,\,12dB$$
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