# Antennas Questions and Answers – Yagi – Uda Antenna

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This set of Antennas Assessment Questions and Answers focuses on “Yagi – Uda Antenna”.

1. The directivity of Yagi-Uda antenna is increased by adding ______
a) reflectors
b) driven element
c) directors
d) boom

Explanation: Addition of directors leads to focus the beam in the forward direction. So, directors will increase the gain of antenna. Folded dipole acts like a feed or driven element. Reflectors will increase the directivity of antenna by reflecting all energy towards radiation direction of antenna. Boom is a center rod on which elements are mounted.

2. Directors are used to increase ______ of the Yagi-Uda antenna.
a) Directivity
b) Gain
c) Back lobe
d) Reflection away from the radiation

Explanation: Reflectors will increase the directivity of antenna by reflecting all energy towards radiation direction of antenna. Addition of directors leads to focus the beam in the forward direction. So, directors will increase the gain of antenna.

3. What is the radiation pattern of a Yagi-Uda antenna?
b) End-fire
c) Collinear

Explanation: Radiation pattern of a Yagi-Uda antenna is end-fire. It has its main beam parallel to the axis of antenna (boom). The addition of directors will increase the gain of antenna while reflectors will increase the directivity of antenna.

4. A narrow beam-width is obtained through a large number of directors.
a) True
b) False

Explanation: Large number of directors increases the direction of radiation towards the desired direction and a narrow beam-width is obtained. It also helps in increasing the directivity of antenna.

5. The dipole to which the power is applied directly from the feeder in the Yagi-Uda antenna is called as _____
a) Director
b) Reflector
c) Driven element
d) Boom

Explanation: The dipole to which the power is applied directly from the feeder in the Yagi-Uda antenna is called driven element. Directors add the field of the driven element and will excite the next parasitic element. Reflectors will increase the directivity of antenna.

6. Folded dipole is used than a single dipole in Yagi-Uda to obtain wider frequency range.
a) True
b) False

Explanation: Folded dipole produces flatter impedance v/s frequency compared to single dipole. So, folded dipole is used in Yagi-Uda to obtain wider frequency range.

7. In which of the following bands Yagi-Uda antenna operates?
a) HF-UFH
b) VLF-MF
c) LF-HF
d) UHF-EHF

Explanation: Yagi-Uda antenna operates mostly in the HF to UFH band frequency. IT ranges from 3MHz to 3GHz.
VLF-MF: 3 kHz to 3MHz
LF-HF: 30 kHz to 30MHz
UHF –EHF: 300MHz to 300GHz.

8. A Yagi-Uda antenna is ____
a) Only a super directive antenna
b) Only a super gain antenna
c) Both super directive and super gain
d) Neither super directive nor super gain

Explanation: A Yagi-Uda antenna provides high directivity by increasing reflectors and gain due to the directors. Directors will increase the forward gain of the antenna. So it is both super directive and super gain antenna.

9. In order to convert the bidirectional dipole to unidirectional system, we use _______
a) Active element
b) Driven element
c) Parasitic element
d) Isolator

Explanation: We use reflectors and directors which are passive elements also known as the parasitic elements to increase the directivity and gain if the antenna.

10. Which of the following will add the field of the driven element and will excite the next parasitic element to increase the gain of the antenna?
a) Director
b) Reflector
c) Active element
d) Boom