# Antennas Questions and Answers – Phased Array – Basics

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Phased Array – Basics”.

1. In which of the following a single radiator source is used to feed antenna with different phase shifts?
a) Phased array

Explanation: In phased array radar a single radiator is used to feed antenna with different phase shifts and thus the desired beam width is obtained. The beam of phased array radar is a synthesis of the multiple antennas used at different phase shifts. In FMCW, Monopulse, CW radar multiple antennas are not usually used at different phase shifts.

2. Which of the following principle is used in the phased array radar?
a) Interference
b) Diffraction
c) Reflection
d) Refraction

Explanation: In phased array radar a single radiator is used to feed antenna array with different phase shifts. When the signals are in-phase the superposition occurs and out of phase cancellation takes place. Thus it is able to steer the beam to required direction.

3. Electronic scanning is more advantageous compared to mechanical scanning
a) True
b) False

Explanation: Electronic scanning is flexible and also requires low maintenance. Electronic scanning is composed of phase shifters, electrical circuits that steer the beam. So Electronic Scanning is better compared to mechanical scanning.
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4. What is the phase shift of the array is the scan angle is 30° and spacing distance is λ/2?
a) $$\frac{π}{2}$$
b) π
c) 2π
d) $$\frac{π}{4}$$

Explanation: The phase $$ᴪ=\frac{2π}{λ} dsinθ=\frac{2π}{λ} \frac{λ}{2} sin30=\frac{π}{2}$$

5. Which of the following equation gives the incremental phase shift of the phase array radar with d element spacing and scan angle θ?
a) $$ᴪ=\frac{2π}{λ} dsinθ$$
b) $$ᴪ=\frac{2π}{d} λsinθ$$
c) $$ᴪ=\frac{π}{λ} dsinθ$$
d) $$ᴪ=\frac{π}{d} λsinθ$$

Explanation: The incremental phase shift of the phase array radar with d element spacing and scan angle θ is given by $$ᴪ=\frac{2π}{λ} dsinθ$$. The phase shifters are electronically tuned to adjust from 0 to 2π.
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6. In Frequency scanning, the phase of all radiators is constant for the frequency tuned at that instant
a) True
b) False

Explanation: In frequency scanning, for one frequency all radiators will be in phase. As the frequency is changed then a corresponding phase shift occurs and the beam is scanned.

7. In which of the following type of scanning a heterodyne is used?
a) IF Scanning
b) Frequency scanning
c) Phase scanning
d) Digital beam-forming

Explanation: At receiving the signals received are heterodyned to IF (Intermediate frequency). The remaining methods of scanning like beam forming are applicable. In IF scanning the heterodyne is used. In frequency scanning the frequency is varied while in phase scanning the phase of the radiators is varied.

8. In which of the following scanning the phase of the radiator is constant at one frequency?
a) Phase scanning
b) Frequency scanning
c) Both Phase and frequency scanning
d) Neither Frequency nor Phase scanning

Explanation: In frequency scanning, for one frequency all radiators will be in phase. As the frequency is changed then a corresponding phase shift occurs and the beam is scanned. In phase scanning the phase shifters are used and radiators have different phases.

9. Which of the following is mainly used in electronic scanning?
a) Phase shifters
b) Amplifiers
c) Repeaters
d) Limiters

Explanation: Electronic scanning is flexible and also requires low maintenance. Electronic scanning is composed of phase shifters, electrical circuits that steer the beam. For the beam to change its direction, the phase of the radiators has to be changed and so the phase shifters used.

10. In which of the following scanning the phase of the radiators varies incrementally for scan?
a) Phase scanning
b) Frequency scanning
c) IF scanning
d) Beam forming

Explanation: In phased array radar a single radiator is used to feed antenna with different phase shifts and thus the desired beam width is obtained. In phase scanning the phase shifters are used and radiators have different phases. The incremental phase shift of the phase array radar with d element spacing and scan angle θ is given by $$ᴪ=\frac{2π}{λ} dsinθ.$$

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