Antenna and Wave Propagation – Previous Year Questions (ECE)
1. The radiation resistance of a short dipole antenna is given by:
A) \( 80\pi^2 \left(\frac{l}{\lambda}\right)^2 \)
B) \( 40\pi^2 \left(\frac{l}{\lambda}\right)^2 \)
C) \( 20\pi^2 \left(\frac{l}{\lambda}\right)^2 \)
D) \( 160\pi^2 \left(\frac{l}{\lambda}\right)^2 \)
Answer: ✅ A
2. For a half-wave dipole antenna, the directivity is approximately:
A) 1.5
B) 2.15 dBi
C) 3 dBi
D) 6 dBi
Answer: ✅ B
3. The beamwidth (HPBW) of a uniform linear array with 10 isotropic elements and spacing \( d = \frac{\lambda}{2} \) is approximately:
A) 10°
B) 20°
C) 12°
D) 36°
Answer: ✅ D
4. The gain (G) of an antenna is related to its directivity (D) and efficiency (η) as:
A) \( G = D + η \)
B) \( G = D \times η \)
C) \( G = \frac{D}{η} \)
D) \( G = D^{η} \)
Answer: ✅ B
5. A broadside array radiates maximum energy:
A) Along the array axis
B) Perpendicular to the array axis
C) At 45°
D) In all directions equally
Answer: ✅ B
6. The end-fire array radiates maximum power:
A) Perpendicular to array axis
B) Along the array axis
C) Opposite to array axis
D) Isotropically
Answer: ✅ B
7. The Friis transmission formula is valid for:
A) Near-field region
B) Far-field region
C) Reactive near field
D) Intermediate field
Answer: ✅ B
8. The effective aperture of an antenna is related to its gain as:
\( A_e = \frac{G \lambda^2}{4\pi} \)
Answer: ✅ True
9. The radiation pattern of an isotropic radiator is:
A) Figure-8
B) Hemispherical
C) Spherical
D) Directional
Answer: ✅ C
10. The polarization of an electromagnetic wave is determined by:
A) Magnetic field direction
B) Electric field direction
C) Propagation direction
D) Wave impedance
Answer: ✅ B
11. The maximum effective aperture of a half-wave dipole is approximately:
A) \( 0.1\lambda^2 \)
B) \( 0.13\lambda^2 \)
C) \( 0.25\lambda^2 \)
D) \( 0.5\lambda^2 \)
Answer: ✅ B
12. For a parabolic dish antenna, the gain is proportional to:
A) \( \lambda^2 \)
B) \( \frac{1}{\lambda^2} \)
C) \( \frac{1}{\lambda^4} \)
D) \( \lambda^4 \)
Answer: ✅ B
13. The power radiated by an isotropic antenna with input power \( P_t \) and gain \( G_t \) at distance \( R \) is proportional to:
\( \frac{P_t G_t}{4\pi R^2} \)
Answer: ✅ True
14. In sky wave propagation, the signal is reflected by:
A) Troposphere
B) Ionosphere
C) Stratosphere
D) Magnetosphere
Answer: ✅ B
15. The skip distance in ionospheric propagation depends on:
A) Frequency
B) Height of ionospheric layer
C) Angle of incidence
D) All of the above
Answer: ✅ D
16. For line-of-sight (LOS) communication, the range increases with:
A) Increase in frequency
B) Increase in antenna height
C) Decrease in antenna height
D) Decrease in power
Answer: ✅ B
17. Antenna bandwidth is inversely proportional to:
A) Antenna size
B) Antenna quality factor (Q)
C) Frequency
D) Wavelength
Answer: ✅ B
18. The radiation pattern of a parabolic reflector antenna is:
A) Omnidirectional
B) Pencil beam
C) Cardioid
D) Dumbbell
Answer: ✅ B
19. Directive gain of an antenna is the ratio of:
A) Radiated power to total power
B) Power in a given direction to average radiated power
C) Received power to transmitted power
D) Effective height to wavelength
Answer: ✅ B
20. Loop antennas are mainly used for:
A) HF long-distance communication
B) Direction finding
C) Microwave links
D) Satellite tracking
Answer: ✅ B
These questions are useful for GATE, ISRO, DRDO, SSC JE, and Polytechnic Lecturer (ECE) exams.
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