# Antennas Questions and Answers – Binomial Array

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

1. Which of the following array is used to synthesize pattern without side lobes?
a) Binomial array
b) Linear array
c) End-fire array
d) Chebyshev array

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.

2. The excitation amplitudes of the binomial array follow ____________
a) Pascal’s triangle
b) Bermuda triangle
c) Right angled triangle
d) Natural squares

Explanation: The excitation amplitudes of the binomial array follow a Pascal’s triangle.

```   1
1 1
1 2 1
1 3 3 1
```

The array factor AF = (1-z)N-1 and N is number of elements.

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3. Which of following is the disadvantage of the binomial array?
a) It has low amplitude variations
b) It has high range of amplitude variations
c) It has a high HPBW
d) It has low HPBW

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.

4. Binomial array has high HPBW compared to Dolph-chebychev.
a) True
b) False

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.
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5. Which of the following can be the excitation amplitude of binomial array with 4 elements?
a) 1 3 3 1
b) 1 2 3 1
c) 2 1 1 2
d) 1 4 6 4 1

Explanation: The excitation amplitudes of the binomial array follow a Pascal’s triangle.

```     1	            N=1
1 1     	    N=2
1 2 1   	    N=3
1 3 3 1	    N=4
```

The array factor AF = (1+z)N-1 and N is number of elements.

6. Dolph- Chebyshev becomes a Binomial array when there are no side lobes.
a) True
b) False

Explanation: 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.

7. What will be the array factor in polynomial form for the 3 element binomial array if Z=e^(-iᴪ)?
a) 1+2z+z2
b) 1+3z+3z2+z3
c) 1+2z+3z2+z3
d) 1+3z+z2

Explanation: The array factor AF = (1+z)N-1 and N is number of elements.
AF = (1+z)3-1 = (1+z)2 = 1+2z+z2
Binomial array follows the Pascal’s triangle coefficients

```     1	            N=1
1 1     	    N=2
1 2 1   	    N=3
1 3 3 1	    N=4.
```

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