Electromagnetic theory miscellaneous
- A half wave dipole capable of radiating 1 kW and has 2.15 dB over a isotropic antenna. How much power must be delivered to the isotropic omnidirectional antenna, to match the field strength of directional antenna?
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Given P1 = 1 kW (Power of unidirectional antenna)
P2 =? (Power delivered)
Gain in dB = 2.15
Now,2.15 = 10 log10 P2 1000
or
P2 = 1000 × 10.215
or
P2 = 1640. 589
or
P2 ≈ 1641 watt
Correct Option: D
Given P1 = 1 kW (Power of unidirectional antenna)
P2 =? (Power delivered)
Gain in dB = 2.15
Now,2.15 = 10 log10 P2 1000
or
P2 = 1000 × 10.215
or
P2 = 1640. 589
or
P2 ≈ 1641 watt
- An antenna has a power input of 40 π watts and a efficiency of 90%. The radiation intensity has to have a max of 150 W/unit solid angle. Directivity—
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We know,
D = G → gain of antenna → efficiency of antenna Gain η Gain = 150 × 4π (Output power) = 15 40π (input power)
and directivity,D = 15 = 15 = 16.67 η 0.9
Correct Option: B
We know,
D = G → gain of antenna → efficiency of antenna Gain η Gain = 150 × 4π (Output power) = 15 40π (input power)
and directivity,D = 15 = 15 = 16.67 η 0.9
- The approximate gain of a parabolic reflector antenna at operating frequency 40 GHz diameter 20 m and illumination efficiency is 55%—
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Gain GP = 4π . Ae 4π . AK λ2 c 2 f = 4π × πD2 . (65) 3 × 108 2 4 4 × 109 = 4π × 42 × π 202 × (.065) 0.09 4
= 1.139 × 105Correct Option: C
Gain GP = 4π . Ae 4π . AK λ2 c 2 f = 4π × πD2 . (65) 3 × 108 2 4 4 × 109 = 4π × 42 × π 202 × (.065) 0.09 4
= 1.139 × 105
- Calculate the front-to-back ratio of an antenna in dB which radiates 3 kW in its most optimum direction and 500 watts in the opposite direction—
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Front to back ratio
GdB = 10 log10 3000 300
= 10 log106 = 7.782Correct Option: B
Front to back ratio
GdB = 10 log10 3000 300
= 10 log106 = 7.782
- A thin dipole antenna is λ/15 metre long. If Its loss resistance is 1.5 Ω. Find radiation resistance and efficiency—
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Rr = 80 π2 dl 2 = 80 π2 λ/15 2 λ λ = 80π2 = 3.5Ω 225 η = Rr = 3.5 Rr + Rl 3.5 + 1.5
orη % = 3.5 × 100 = 70% 5 Correct Option: B
Rr = 80 π2 dl 2 = 80 π2 λ/15 2 λ λ = 80π2 = 3.5Ω 225 η = Rr = 3.5 Rr + Rl 3.5 + 1.5
orη % = 3.5 × 100 = 70% 5