Microwave antenna

Focus points for the secondary and primary reflectors will meet at the same point.

CASSEGRAIN FEED

• Focus points for the secondary and primary reflectors will meet at the same point.
• Radiation from the horn antenna will be reflected by the secondary reflector and transmitted to the primary reflector to collimate the radiation.

Similar to the Cassegrain design except that the secondary reflector is concave, (ellipsoidal) in shape.

GREGORIAN FEED

• Similar to the Cassegrain design except that the secondary reflector is concave, (ellipsoidal) in shape.
• Aperture efficiency over 70% can be achieved.

It is widely used as a primary feeder, because of the flaring directivity pattern , thus preventing refraction.

HORN FEED

• It is widely used as a primary feeder, because of the flaring directivity pattern , thus preventing refraction.

MAIN REFLECTOR
PRIMARY FEED HORN
WAVEGUIDE/TRANSMISSION LINE

RADIATION PATTERN

FACTORS AFFECTING THE ANTENNA

RADIATION PATTERN

Radiation pattern refers to the performance ot the antenna for example when it is mounted far away from objects such as buildings or mountain ( earth) by which reflecting signal might affect the shape of the pattern.
FACTORS AFFECTING THE ANTENNA
Figures below show the 3-dimensional models (polar graf/diagram) of field strength or power density measurements made at a fixed distance from an antenna in a given plane.
FACTORS AFFECTING THE ANTENNA
Figures below show the 3-dimensional models (polar graf/diagram) of field strength or power density measurements made at a fixed distance from an antenna in a given plane.

BEAM WIDTH (BEAM / FLARED ANGLE)

BEAM WIDTH (BEAM / FLARED ANGLE)

• It is the angle subtended by the points at which the radiation power falls to the half of its maximum power.
• In other words, the field strength has fallen to 1/√2 (70.7 % ) of its maximum voltage or the angle measured between the -3dB (half power) points on the major lobe of an antenna’s radiation pattern.