# Antennas Questions and Answers – Uniform Aperture Field

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Uniform Aperture Field”.

1. For aperture antenna to be efficient and have high directivity, its area should be ____________
a) ≥ λ2
b) ≥ 1/λ
c) ≤ λ2
d) ≤ λ

Explanation: Antenna with an aperture at the end is known as aperture antenna. Example is waveguide. For aperture antenna to have high directivity its area should be ≥ λ2. These antennas usually operated at UHF and above frequencies.

2. At which of the following frequencies aperture antennas are operated?
a) UHF and EHF
b) MF and HF
c) HF and UHF
d) LF and MF

Explanation: Antenna with an aperture at the end is known as aperture antenna. Example is waveguide. These antennas usually operated at UHF and EHF frequencies (300MHz to 300GHz).
LF – 30 kHz – 300 kHz
MF – 300k-3MHz
HF – 3MHz -30MHz

3. Which of the following does not belong to the aperture antenna?
a) Half-Dipole
b) Horn Antenna
c) Waveguide antenna
d) Slot antenna

Explanation: Antenna with an aperture at the end is known as aperture antenna. Horn antenna, Waveguide antenna and slot antenna are examples of aperture antenna. Half-dipole is a wire antenna.
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4. Which of the following principle is used for analysis of aperture antennas?
a) Equivalence principle
b) Friss Equation
c) Reflectivity
d) Diffraction

Explanation: Equivalence principle follows the uniqueness theorem. It provides a unique solution for the boundary conditions. So this is used in the analysis of the aperture antennas. Friss transmission is used to relate the distance and power radiation between the antennas. Reflectivity and diffraction are not the principles used for analysis of aperture antenna.

5. Equivalence Principle follows which f the following theorem?
a) Uniqueness Theorem
b) Poynting theorem
c) Friss Theorem
d) Gauss theorem

Explanation: Equivalence principle follows the uniqueness theorem. It provides a unique solution for the boundary conditions. Uniqueness theorem is defined from the pointing theorem. Friss transmission is used to relate the distance and power radiation between the antennas. Gauss theorem states that total electric flux enclosed by charge is equal to net positive charge.
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6. Which of the following condition is true for the electric conductor equivalent?
a) Js=n×H=0;Ms=-n×E
b) Js=n×H;Ms=-n×E=0
c) Js=n×H≠0;Ms=-n×E
d) Js=n×H≠0;Ms=-n×E=0

Explanation: The equivalent surface currents Js, Ms radiates fields H, E respectively. The conditions for the electric conductor equivalent is Js=n×H=0;Ms=-n×E.

7. Which of the following condition is true for the magnetic conductor equivalent?
a) Js=n×H=0;Ms=-n×E
b) Js=n×H;Ms=-n×E=0
c) Js=n×H≠0;Ms=-n×E
d) Js=n×H≠0;Ms=-n×E=0

Explanation: The equivalent surface currents Js, Ms radiates fields H, E. The conditions for the electric conductor equivalent is Js=n×H;Ms=-n×E=0. This is one of the equivalence principle modes.

8. Equivalence principle is mainly used for far filed analysis of the antenna in outer region.
a) True
b) False

Explanation: Equivalence principle follows the uniqueness theorem. It provides a unique solution for the boundary conditions. So this is used in the far field analysis of the aperture antennas in the outer regions.

9. The gain of the aperture antenna increases with square of the frequency.
a) True
b) False

Explanation: One of the distinguishing features of the aperture antenna is the increase in gain with operating frequency. The gain of the aperture antenna increases with square of the frequency if its aperture efficiency is kept constant with respect to the frequency.

10. Huygens principle in mathematical form is referred to as equivalence principle for aperture antennas.
a) True
b) False

Explanation: The equivalence principle replaces the aperture antenna with surface currents and thereby fields. It is derived from the uniqueness theorem and provides a unique solution for the boundary conditions for the fields. This is mainly used for the far field analysis of the aperture antenna.

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