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The CORRECT CHOICE is (a) 1 3 3 1

For explanation: The EXCITATION AMPLITUDES of the BINOMIAL array follow a Pascal’s triangle.

Right choice is (a) True

Explanation: BINOMIAL array has WIDE BEAMS and so it has high HPBW. Its HPBW is high compared to Dolph-Chebyshev array. Binomial array is used to synthesize PATTERNS without SIDE lobes.

Correct CHOICE is (a) Tm(z) = 2zTm-1(z) – Tm-2(z)

Best EXPLANATION: The Chebyshev POLYNOMIAL of any ORDER m can be derived from the recursive formula. This is ONE of the main features of the Chebyshev polynomial. It is given by

Tm(z) = 2zTm-1(z) – Tm-2(z).

The CORRECT OPTION is (a) -∞ dB

Best explanation: Dolph –Chebyshev will become binomial array when there are no any SIDE LOBES.

So side lobes a =0

Side lobe level = major lobe level / minor lobe max =0

In dB = 20 log (1/a) = -∞ dB.

Correct option is (B) False

For explanation I would say: All the NULLS in the CHEBYSHEV POLYNOMIAL OCCUR in the range -1≤ x≤1.

(-1, 1) here is representing a point. So it is false.

The correct CHOICE is (a) True

The explanation: The Chebyshev POLYNOMIAL is given by

T0(x) = 1 m=0

T1(x) = x m=1

T2(x) = 2x^2-1 m=2

T3(x) = 4x^3-3x m=3

As the order of the polynomial increases, the SLOPE BECOMES steeper.

Right ANSWER is (a) The minor lobes have unequal amplitudes

Explanation: The minor lobes have EQUAL amplitudes. The polynomial Tm(x) CROSSES the x axis m times between -1 and 1.

Minor lobes EXIST for |x| < 1 and MAJOR lobes exist for |x| > 1.

Correct option is (a) BINOMIAL array

For explanation: Binomial array is used to SYNTHESIZE patterns WITHOUT SIDE lobes. In Chebyshev there are side-lobes present below the major beam LEVEL. The excitation amplitudes of the binomial array follow a Pascal’s triangle.

The correct OPTION is (B) 60°

Easiest EXPLANATION: HPBW of the Dolph Chebyshev array= BROADENING factor×HPBW of uniform array

=2×30°=60°.

Correct choice is (a) 1+2z+z^2

To EXPLAIN I would say: The ARRAY factor AF = (1+z)^N-1and N is number of elements.

AF = (1+z)^3-1 = (1+z)^2 = 1+2z+z^2

Binomial array follows the Pascal’s triangle coefficients

Right choice is (a) (1, 1)

Easiest explanation: All the POLYNOMIALS of the order m of the chebyshev pass through the POINT (X, Tm(x))

 = (1, 1).

T0(x) = 1

T1(x) = x

T2(x) = 2x^2-1

T3(x) = 4x^3-3x

The correct OPTION is (a) Dolph-CHEBYSHEV

The EXPLANATION is: Dolph- chebyshev METHOD is used to design array with desired side lobes. It uses the approximation of the Chebyshev polynomials. BINOMIAL array is used to synthesis the patterns without side lobes. Taylor and broad-side array have side lobes.

The correct option is (a) 40dB

Easy explanation: The minor lobes are PRESENT below the MAIN beam level at a VALUE 1/SLL. SLL is the SIDE lobe level.

Possible level for the minor lobe is 50-10=40dB

The correct option is (a) True

The explanation is: Binomial array is USED to synthesize PATTERNS WITHOUT side lobes. Dolph- chebyshev METHOD is used to design array with desired side lobes. When the side lobe of the Dolph DROPS to -∞ dB, it behaves like a binomial array.

Correct choice is (a) It has low AMPLITUDE variations

Explanation: BINOMIAL ARRAY follows a Pascal’s triangle type of amplitude variations. So there are high variations in the amplitudes. Binomial array has high HPBW and hence more WIDE BEAMS are present.

Right answer is (a) 0

To explain I WOULD SAY: The CHEBYSHEV polynomial is GIVEN by

T0(X) = 1 m=0

T1(x) = x m=1

T2(x) = 2x^2-1 m=2

T3(x) = 4x^3-3x m=3

For m=odd; Tm(0) = 0

For m=even; Tm(0) = (-1)^m/2

Right answer is (a) Tm(z) = 2zTm-1(z) – Tm-2(z)

Explanation: The Chebyshev polynomial of any order m can be DERIVED from the RECURSIVE FORMULA. This is one of the main features of the Chebyshev polynomial. The RECURRENCE relation for the Chebyshev polynomial is

Tm(z) = 2zTm-1(z) – Tm-2(z).

Correct answer is (a) Woodward

For explanation: Woodward method is suited for beam shaping and the complete pattern and excitation distributions locations are given by the Fourier method. The nulls in specified pattern are produced by the Schelkunoff method. The TAYLOR synthesis has a CONSTANT inner MINOR lobes level.

The correct option is (a) True

To explain I WOULD say: 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.

Right answer is (a) SPACE feed

The best explanation: In space feed, the energy is distributed to the lens ARRAY in a MANNER analogous to point feed illuminating a reflect antenna. In constrained the power is divided into many elements under different steps. In optical feed systems power is divided in one STEP. Parallel plate feed USES microwave structure principles and provides efficient power division.

The correct answer is (a) array FEED

The explanation: The power DIVIDER used to connect array elements to single port is called array feed. Array feeds are classified into three types: Constrained feeds, OPTICAL feed/ space feed, PARALLEL PLATE feed.

The correct OPTION is (a) 5

Best explanation: The polynomial TM(x) crosses the x AXIS m times between -1 and 1. Given polynomial is T5(x).

M=5 therefore it crosses the axis 5 times between [-1, 1].

The correct ANSWER is (a) Adaptive arrays

Explanation: The adaptive arrays are extensively USED to detect the NOISE interference in the desired signal and suppress them. It is a combination of ARRAY sensors and real time adaptive signal receiver PROCESSOR.

The correct choice is (a) Adaptive array

To explain: In adaptive array a real time adaptive signal processor is used to detect and nullify the NOISE interference. Phased array is used to steer the beam. Pulse RADAR is used to KNOW the target DISTANCE and CW radar is used to the VELOCITY of the target.

The correct answer is (a) Series end FED

Easiest explanation: In series end fed, the radiator is placed at the end of the array and its electrical path length DEPENDS on the frequency. In CENTER fed, radiator is PROVIDED at the center of the array and has bandwidth similar to the parallel FEED network. In parallel feed, a number of radiators are combined into sub-arrays and then to elements in series or center fed.

Correct option is (a) Constrained feed systems

For explanation I would say: The power is DIVIDED into many elements under different steps in constrained feed systems. Phased array ANTENNAS with LENS or reflector arrays belong to the optical feed system. Proper aperture illumination is obtained through the optical feed system and systems power is divided in ONE step.

Correct ANSWER is (b) Frequency SCANNING

The best 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.

The CORRECT choice is (a) \(ᴪ=\frac{2π}{λ} dsinθ\)

Easiest 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.

The correct answer is (a) Phase scanning

To EXPLAIN I would SAY: 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 \(ᴪ=\frac{2π}{λ} dsinθ. \)

The correct CHOICE is (a) IF Scanning

The explanation is: 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.

The CORRECT CHOICE is (a) \(\FRAC{π}{2} \)

To explain: The PHASE \(ᴪ=\frac{2π}{λ} dsinθ=\frac{2π}{λ} \frac{λ}{2} sin30=\frac{π}{2} \)

The correct option is (a) OPTICAL-feed system

The best explanation: Phased array with lens or reflector arrays comes under the optical feed system. Proper aperture illumination is OBTAINED by the optical feed system. In CONSTRAINED the POWER is DIVIDED into many elements under different steps.

Correct option is (a) Chebyshev

Easiest explanation: Chebyshev TECHNIQUE is used to obtain array with any desired side lobe level. In Schelkunoff METHOD, PATTERN is PRODUCED with null in SPECIFIED directions. Woodward method is suited for beam shaping. Binomial array is used when no side lobes are desired.

Right OPTION is (a) True

Easy explanation: One of the PROPERTIES exhibited by the Chebyshev array is having a constant amplitude range of 1-≤x≤1. Its array factor is APPROXIMATED to Chebyshev polynomial. This array has constant side lobes and elements are placed UNIFORMLY.

Right answer is (a) Phase shifters

For explanation I would say: 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.

Right choice is (B) Center fed ARRAY

For explanation I would say: The Center fed array in the series feed network has same bandwidth as the PARALLEL feed NETWORKS. The end fed array has several bandwidth restrictions.