# Reflector Antenna Questions and Answers – Basics

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

1. Which of the following refers to the pattern of reflector in the reflector antenna?
a) Primary pattern
b) Secondary pattern
c) Reflector pattern
d) Feed pattern

Explanation: In a reflector antenna, primary pattern is the feed pattern and secondary pattern is the pattern of reflector. Reflector antennas are high gain antenna and are used in RADARs and for some communication purpose.

2. Reflector antenna operates on the Geometric optics principle?
a) True
b) False

Explanation: Reflector antenna is high gain antenna and works on the principle of the Geometric optics. Geometrical optics shows that if a beam of parallel rays is incident on a reflector antenna whose geometrical shape is a parabola, then the array beams will converge at the focal point.

3. Which of the following is a dual reflector antenna?
a) Cassegrain antenna
b) Parabolic antenna
c) Offset reflector antenna
d) Wire antenna

Explanation: A dual reflector antenna consists of two reflectors and one feed antenna. Cassegrain antenna is the best example of dual reflector antenna since it contains main reflector as parabolic and sub-reflector as hyperbola.

4. Which of the following combination forms a Cassegrain antenna?
a) The main reflector is parabolic and sub-reflector is hyperbolic
b) The main reflector is parabolic and sub-reflector is concave
c) The main reflector is hyperbolic and sub-reflector is parabolic
d) The main reflector is hyperbolic and sub-reflector is convex

Explanation: A Cassegrain antenna is a dual reflector antenna and is axis symmetry. It consists of two reflectors and one primary feed. The main reflector is parabolic and sub-reflector is hyperbolic (convex).

5. Which of the following efficiency is used to measure the power-loss at the feed pattern which is intercepted by reflector?
a) Spillover
b) Illumination
c) Taper
d) Aperture

Explanation: When the feed pattern exceeds beyond reflectors rim, not all the energy is redirected by the reflector. This power loss is measure results in spillover efficiency. Illumination efficiency is the combination of both taper and spillover efficiency. Aperture efficiency is the ratio of effective aperture to physical aperture. Taper efficiency gives the directivity measure of the antenna.

6. What is the value of magnification of the Cassegrain antenna if its sub-reflector eccentricity is 2?
a) 3
b) 2
c) 1/3
d) 1/2

Explanation: Given eccentricity e=2
Magnification $$M=\frac{e+1}{e-1}=3$$

7. Which of the following is false regarding a reflector antenna?
a) Reflector antennas are high gain antennas with two antennas
b) Both the primary and secondary antennas are excited
c) The pattern of the reflector in the reflector antenna is the Secondary pattern
d) A dual reflector contains two reflectors and one primary feed

Explanation: In a reflector antenna the horn or a dipole acts as a feed and the antenna which is excited is the primary antenna. Reflector is the secondary antenna. Reflector antenna is a high gain antenna consisting of primary and secondary antennas.

8. Which of the following is not a reflector antenna?
a) Convex-convex
b) Corner
c) Gregorian
d) Cassegrain

Explanation: Corner, Cassegrain and Gregorian belong to reflector antenna. Convex-convex is a type of lens antenna. Gregorian is a dual reflector antenna with a concave sub-reflector.

9. When a reflector is placed at the foci along the feed it is called ____ antenna
a) Dual reflector antenna
b) Plane antenna
c) Wire antenna
d) Convex-Convex

Explanation: Usually a feed forward is used in reflector antenna and feed antenna is placed at focus of the reflector. When a sub-reflector is placed at the focus along with the feed antenna it is called dual reflector antenna. Example of dual reflector antenna: Cassegrain antenna.
Convex-Convex is a lens antenna.

10. Which of the following is used as a secondary antenna in the reflector antenna?
a) Horn
b) Feed antenna
c) Parabolic
d) Dipole