Array Antenna Quiz - Electrical Engineering

Instructions: This quiz contains 12 multiple-choice questions on array antennas. Select the best answer for each question. After completing all questions, click "Submit Quiz" to see your score and review the answers with detailed explanations.

1 What is the primary advantage of using an antenna array compared to a single antenna element?

A. Reduced size and weight

B. Lower power consumption

C. Controllable radiation pattern through constructive and destructive interference

D. Simpler design and manufacturing

2 In a uniformly excited, equally spaced linear array, what determines the direction of the main beam?

A. The amplitude distribution across elements

B. The progressive phase shift between adjacent elements

C. The physical spacing between elements

D. The frequency of operation

3 What is the array factor (AF) for an N-element linear array with uniform amplitude and spacing?

A. AF = Σ I_n e^j(n-1)ψ, where ψ = kd cosθ + β

B. AF = Σ I_n e^j(n)ψ, where ψ = kd sinθ

C. AF = N, a constant value

D. AF = Σ I_n cos(nψ), where ψ = kd cosθ

4 What phenomenon occurs when the element spacing in an array exceeds λ/2 for broadside arrays?

A. Reduced directivity

B. Grating lobes - additional main beams in undesired directions

C. Complete signal cancellation

D. Frequency shift in operation

5 In a phased array antenna, beam steering is typically achieved by:

A. Mechanically rotating the entire array

B. Varying the amplitude excitation of each element

C. Applying a progressive phase shift across the array elements

D. Changing the operating frequency

6 What is the half-power beamwidth (HPBW) of a broadside uniform linear array with many elements?

A. Inversely proportional to the array length in wavelengths

B. Directly proportional to the number of elements

C. Constant regardless of array size

D. Proportional to the square of the element spacing

7 Which amplitude distribution in an array antenna provides the lowest sidelobe levels?

A. Uniform distribution

B. Triangular distribution

C. Binomial distribution

D. Dolph-Chebyshev distribution

8 The directivity of a linear array antenna increases with:

A. Decreasing number of elements

B. Increasing element spacing beyond λ/2

C. Increasing array length in wavelengths

D. Decreasing operating frequency

9 What is the main purpose of using a non-uniform amplitude distribution (tapering) in array antennas?

A. To increase the main beamwidth

B. To reduce sidelobe levels at the expense of increased beamwidth

C. To simplify the feeding network

D. To eliminate the need for phase shifters

10 For an end-fire array, the progressive phase shift between elements (β) should be approximately:

A. β = 0°

B. β = ±90°

C. β = ±kd (where k is the wave number and d is element spacing)

D. β = 180°

11 What is a planar array antenna primarily used for?

A. To achieve beam steering in two dimensions (azimuth and elevation)

B. To reduce the physical size of the antenna

C. To operate at lower frequencies

D. To eliminate grating lobes completely

12 In adaptive array antennas, what is the main function of the adaptive algorithm?

A. To maximize the directivity regardless of interference

B. To automatically adjust amplitude and phase weights to optimize performance in changing environments

C. To maintain constant beamwidth across all frequencies

D. To reduce manufacturing costs