Parabolic antenna
Introduction
A parabolic antenna is a high-gain type of antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct the radio waves in a narrow beam, or receive radio waves from one particular direction only.
Design and Function
Parabolic antennas have a parabolic reflector and a small feed antenna at its focus. The feed antenna at the focus is typically a low-gain type such as a half-wave dipole or a small horn. In a transmitting antenna, radio frequency current from a transmitter is supplied through a transmission line running from the transmitter to the feed antenna. The feed antenna converts the radio frequency alternating current into radio waves. The waves are emitted back toward the reflector, so the antenna directs them into a beam. In a receiving antenna, the incoming radio waves bounce off the reflector and are focused onto the feed antenna at the focal point, converting them to radio frequency alternating current which is applied to a receiver.
Types of Parabolic Antennas
There are several types of parabolic antennas: standard, offset, Cassegrain, Gregorian, dual reflector, and multi-beam and shared aperture.
Standard
The standard parabolic antenna consists of a parabolic reflector with a small feed antenna at its focus. This is the most common type of parabolic antenna.
Offset
An offset parabolic antenna is a type of parabolic antenna. It is so called because the feed antenna is offset to the side of the reflector, in contrast to the common "front-feed" parabolic antenna where the feed antenna is located in front of the reflector at its focus.
Cassegrain
In a Cassegrain antenna, the feed antenna is located behind the parabolic reflector and is aimed at a smaller flat reflector at the focus of the parabola.
Gregorian
A Gregorian antenna is similar to the Cassegrain antenna but uses a second parabolic reflector instead of a flat one.
Dual Reflector
A dual reflector antenna is a design similar to the Cassegrain and Gregorian but with additional adjustments to improve performance.
Multi-beam and shared aperture antennas are complex designs that allow for multiple simultaneous beams or feeds.
Applications
Parabolic antennas are used in many types of communication as a high-gain antenna. They are used as high-gain antennas for point-to-point communications, in applications such as microwave relay links that carry telephone and television signals between nearby cities, wireless WAN/LAN links for data communications, satellite communications and spacecraft communication antennas.
