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51.	Which of the following is not a benefit of the adaptive array technology?(a) Co-channel interference reduction(b) Reduction in multipath interference(c) Increase in multipath interference(d) Reduction in handoffsI got this question in quiz.The doubt is from Adaptive Array in chapter Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct answer is (c) Increase in multipath interference To elaborate: Adaptive array place nulls in unwanted direction/interference and are used to GUIDE the beam in desired direction. These are used to SUPPRESS the noise interference in desired direction. So, the HANDOFFS, co-channel interference, multipath interference are reduced with the help of the ADVANCED DIGITAL signal processors and the complex algorithms.

52.	Which of the following is holds true for the Chebyshev polynomial?(a) Tm(-x) = (-1)^m Tm(x)(b) Tm(-x) = (-1)^m Tm-1(1/x)(c) Tm(x) = (-1)^m Tm(1/x)(d) Tm(-x) = (-1)^m Tm-1(x)This question was posed to me during a job interview.My enquiry is from Adaptive Array topic in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct OPTION is (a) TM(-x) = (-1)^m Tm(x) The best EXPLANATION: The Chebyshev polynomial is given by T0(x)=1m=0 T1(x)=xm=1 T2(x)=2x^2-1m=2 T3(x)=4x^3-3xm=3 There fore Tm(-x)=(-1)^m Tm (x) holds true.

53.	In which of the following radiators are combined into sub-arrays and then fed to elements in end or center fed?(a) Parallel feed(b) Series feed(c) Optical feed system(d) Series end feedThe question was asked in a national level competition.The above asked question is from Phased Array topic in division Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct option is (a) Parallel feed Best explanation: In parallel feed, a NUMBER of radiators are combined into sub-arrays and then to elements in series or center fed. In series END fed, the radiator is placed at the end of the array and its electrical path length depends on the frequency.In optical feed SYSTEMS power is DIVIDED in one STEP.

54.	Adaptive arrays provide best results compared to switching beams under more interference.(a) True(b) FalseI have been asked this question in an online quiz.Question is taken from Adaptive Array in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» Right ANSWER is (a) True Explanation: Switching beams provide intra cellular handoffs but also works best only at less or nil INTERFERENCE. The adaptive arrays can be used under more interference. These are used to detect the noise interference in the desired signal and SUPPRESS them. Adaptive array CONSISTS of array sensors and real time adaptive signal receiver PROCESSOR.

55.	In which of the following a single radiator source is used to feed antenna with different phase shifts?(a) Phased array(b) FMCW radar(c) Monopulse radar(d) CW radarThis question was posed to me in a job interview.Origin of the question is Phased Array in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» Correct option is (a) Phased array The best I can explain: 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.

56.	Which of the following statements is false?(a) The intra cellular handoffs are less in adaptive array compared to switching beams(b) Noise interference cannot be detected in adaptive arrays effectively compared to switching beams(c) Advanced digital signal processors are used in adaptive arrays(d) Algorithms used in adaptive array is more complex than switching beamsThis question was posed to me in my homework.Question is from Adaptive Array topic in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» Right answer is (B) Noise interference cannot be DETECTED in adaptive arrays effectively compared to switching beams The best I can EXPLAIN: Adaptive array is used to guide the BEAM in desired direction and place nulls in unwanted direction/interference. More complex algorithms are used in adaptive arrays and also advance digital signal processors are used to DIFFERENT the desired user and the unwanted signals/users.

57.	Which of the following statement is true about the Chebyshev function Tm(x)?(a) It is a continuously increasing function after x=1(b) It is a continuously decreasing function after x=1(c) It is a continuously increasing function after x=0(d) It is a continuously decreasing function after x=0This question was posed to me at a job interview.This key question is from Adaptive Array topic in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» Right option is (a) It is a continuously INCREASING function after x=1 The best EXPLANATION: T0(x) = 1 T1(x) = x T2(x) = 2x^2-1 ⇨ T3(x) = 4x^3-3x This is the chebyshev polynomial and it INCREASES continuously after x=1

58.	What is the value of Tm (0) when m is an even number?(a) 0(b) (-1)^m(c) -1(d) (-1)^m/2The question was posed to me during an online exam.My doubt is from Adaptive Array in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» RIGHT choice is (d) (-1)^m/2 The BEST I can explain: 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=even; Tm(0) = (-1)^m/2

59.	The value of Tm(-1)=_______(a) (-1)^m(b) (-1)^m-1(c) (-1)^m/2(d) (-1)^2mThe question was asked in examination.I'm obligated to ask this question of Adaptive Array in section Phased, Adaptive and Binomial Arrays of Antennas
Answer» CORRECT answer is (a) (-1)^m Best explanation: The Chebyshev POLYNOMIAL is GIVEN by T0(X) = 1m=0 T1(x) = xm=1 T2(x) = 2x^2-1m=2 T3(x) = 4x^3-3xm=3 ThereforeTm(-1)=(-1)^m.

60.	___ is used to guide the beam in desired direction and place nulls in unwanted direction/interference.(a) Adaptive array(b) Switching beams(c) Phased radar(d) Pulse radarThis question was posed to me in semester exam.My question comes from Adaptive Array topic in section Phased, Adaptive and Binomial Arrays of Antennas
Answer» Correct option is (a) Adaptive array Best explanation: The adaptive arrays are extensively USED to detect the NOISE INTERFERENCE in the desired signal and suppress them. The ADVANCED digital signal processing in the adaptive arrays helps to reduce the interference compared to switch beams. Pulse radars are used to know the distance of target. Phased array radars steer the BEAM in desired direction.

61.	The noise detection and suppression is possible with adaptive arrays.(a) True(b) FalseThis question was posed to me in class test.This interesting question is from Adaptive Array in chapter Phased, Adaptive and Binomial Arrays of Antennas
Answer» CORRECT option is (a) True The best explanation: The noise can be detected and can be SUPPRESSED in DESIRED direction using the adaptive arrays. Adaptive arrays are COMBINATION of array sensors along REAL time adaptive signal receiver processor.

62.	A folded pillbox antenna is used in which of the following feeding system?(a) Parallel plate feed(b) Space feed(c) Optical feed system(d) Constrained feed systemThe question was asked in semester exam.Asked question is from Phased Array in chapter Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct option is (a) PARALLEL plate FEED To explain I would say: Folded pillbox antenna is used to PROVIDE the POWER distribution to antenna ELEMENTS. So this is used in the parallel plate feed system. Lens and reflect array used in the space/optical feed systems. Constrained feed provides a series and parallel feed combination.

63.	Parallel plate feed is a cross of constrained and space feed.(a) True(b) FalseThe question was asked during an online exam.Query is from Phased Array topic in chapter Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct option is (a) True Easy EXPLANATION: Parallel PLATE feed uses MICROWAVE structure principles and provides efficient power division.In constrained the power is divided into many elements under different steps. In optical feed SYSTEMS power is divided in one step. In space feed, the energy is distributed to the lens array.

64.	Which of the following statement is true?(a) Lens array has different input and output radiators while same radiator is used for reflector array(b) There is no surface matching required for the lens array(c) In lens and reflect array same radiator is used for input and output(d) Lens and reflect array belong to constrained feed systemsThis question was posed to me in my homework.My query is from Phased Array in section Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct answer is (a) Lens ARRAY has different input and output radiators while same radiator is used for reflector array To elaborate: In Lens array, different input and output radiators are used and hence there TWO surface matching is required. In reflect array the same radiator is used to radiate and collect.Phased array with lens or reflector arrays COMES under the optical feed SYSTEM.

65.	In Frequency scanning, the phase of all radiators is constant for the frequency tuned at that instant(a) True(b) FalseI had been asked this question during an interview.The above asked question is from Phased Array in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» CORRECT choice is (a) True To explain I would say: 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.

66.	Which of the following synthesis method have a constant inner minor lobe level and remaining one decreasing gradually?(a) Woodward(b) Schelkunoff(c) Fourier(d) TaylorI have been asked this question in homework.Question is taken from Adaptive Array in portion Phased, Adaptive and Binomial Arrays of Antennas
Answer» CORRECT choice is (d) TAYLOR For explanation: Taylor synthesis has a constant inner minor lobes LEVEL and gradually decreasing lobes for other. Nulls are produced in a specified direction for the PATTERN using Schelkunoff method. The Woodward method is USED for beam shaping in antenna synthesis while Fourier is used when the complete pattern and excitation distributions locations are given.

67.	Antenna synthesis is analogous to _____(a) Antenna array(b) Antenna analysis(c) Antenna radiation(d) Schelkunoff synthesisI have been asked this question in final exam.The question is from Adaptive Array topic in section Phased, Adaptive and Binomial Arrays of Antennas
Answer» The correct CHOICE is (b) Antenna analysis The best I can explain: SCHELKUNOFF is one of the METHODS of antenna synthesis.Antenna synthesis determines the distribution of input or output sources from the OBTAINED radiation pattern. Antenna analysis is determining the radiation pattern for the GIVEN input distribution.

68.	Which of the following is the key feature of the Chebyshev array?(a) Have constant side lobes and elements are placed uniformly(b) Have varying side lobes and elements are placed uniformly(c) Minor lobes are present at \|x\| > 1(d) Major lobes are present at \|x\| < 1I had been asked this question in examination.My query is from Adaptive Array topic in chapter Phased, Adaptive and Binomial Arrays of Antennas
Answer» The CORRECT option is (a) Have constant side LOBES and elements are placed uniformly The explanation: Chebyshev array exhibits the properties of the Chebyshev polynomial having constant amplitude 1-≤X≤1. MINOR lobes are present at \|x\| < 1 andMajor lobes are present at \|x\| > 1.

69.	Which of the following method is used for antenna design with no side lobes?(a) Binomial array(b) Dolph Chebyshev(c) Schelkunoff(d) WoodwardThe question was posed to me in a job interview.I'd like to ask this question from Adaptive Array topic in division Phased, Adaptive and Binomial Arrays of Antennas
Answer» Right option is (a) Binomial array The explanation: Dolph Chebyshev is a special case (at no SIDE lobes) of Binomial array. Dolph Chebyshev is used to design array at DESIRED side lobes. In Schelkunoff method, pattern is produced with NULL in SPECIFIED directions. Woodward method is suited for beam shaping.