This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Introduction”.
1. Which of the following is false regarding Antenna array?
a) Directivity increases
b) Directivity decreases
c) Beam width decreases
d) Gain increases
View Answer
Explanation: A single antenna provides low gain and less directivity. To increase the directivity antenna arrays are used. With the antenna arrays, directivity and gain increases and beam width decreases.
2. Electrical size of antenna is increased by which of the following?
a) Antenna Array
b) Decreasing the coverage area
c) Increasing the coverage area
d) Using a single antenna
View Answer
Explanation: To increase the directivity antenna arrays are used. With the antenna arrays, directivity and gain increases and beam width decreases. The electrical size of the antenna is increased by placing an array antenna together to achieve high directivity.
3. For long distance communication, which of the property is mainly necessary for the antenna?
a) High directivity
b) Low directivity
c) Low gain
d) Broad beam width
View Answer
Explanation: Long distance communication requires antenna with high directivity. To increase the directivity antenna arrays are used. With the antenna arrays, directivity and gain increases and beam width decreases.
4. Which of the following is false about the single antenna for long distance communication?
a) Enlarging may create side lobes
b) No side lobes
c) High directivity is required
d) High Gain is required
View Answer
Explanation: High directive antennas are required for the long distance communications. The array of antennas is used to increase the directivity. The directivity can be increased by increasing the dimensions of antenna but it creates side lobes.
5. The electrical size of antenna is increased by antenna array to avoid size lobes compared to single antenna.
a) True
b) False
View Answer
Explanation: Increasing the dimensions of antennas may lead to the appearance of the side lobes. So by placing a group of antennas together the electrical size of antenna can be increased. With the antenna arrays, directivity and gain increases and beam width decreases.
6. A uniform linear array contains _____________
a) N elements placed at equidistance and fed currents of equal magnitude and progressive phase shift
b) N elements at non-equidistance and fed currents of equal magnitude and progressive phase shift
c) N elements at equidistance and fed currents of unequal magnitude and progressive phase shift
d) N elements at equidistance and fed currents of unequal magnitude and equal phase shift
View Answer
Explanation: An array is said to be linear if N elements are spaced equally long the line and is a uniform array if the current is fed with equal magnitude to all elements and progressive phase shift along the line. High directivity can be obtained by antenna array.
7. Total resultant field obtained by the antenna array is given by which of following?
a) Vector superposition of individual field from the element
b) Maximum field from individual sources in the array
c) Minimum field from individual sources in the array
d) Field from the individual source
View Answer
Explanation: The total resultant field is obtained by adding all the fields obtained by the individual sources in the array. An Array containing N elements has the resultant field equal to the vector superposition of individual field from the elements.
8. If the progressive shift in antenna array is equal to zero then it is called _________
a) Broad side
b) End-fire
c) Yagi-uda
d) Fishbone antenna
View Answer
Explanation: The total phase difference of the fields is given by Ѱ=kdcosθ+β
Here β is the progressive phase shift
⇨ β=0, array is a uniform broadside array
⇨ β=180, array is a uniform end-fire array
Yagi-uda antenna, fishbone antenna are end-fire antenna array.
9. What is the progressive phase shift of the end-fire array?
a) 0
b) 90
c) 180
d) 60
View Answer
Explanation: The progressive phase shift of the end-fire array is 180°. It is a linear array whose direction of radiation is along the axis of the array. For a broadside array it is 0°.
10. Which of the following statement about antenna array is false?
a) Field pattern is the product of individual elements in array
b) Field pattern is the sum of individual elements in array
c) Resultant field is the vector superposition of the fields from individual elements in array
d) High directivity can be achieved for long distance communications
View Answer
Explanation: The total resultant field is obtained by adding all the fields obtained by the individual sources in the array. Radiation pattern is obtained by multiplying the individual pattern of the element. Field pattern is the product of individual elements in array. Antenna arrays are used to get high directivity with less side lobes.
Sanfoundry Global Education & Learning Series – Antennas.
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