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Cassegrain feed-Function and basics of cassegrain

This page describes function and basics of cassegrain feed used in antenna system.

As we know parabolic dish antenna is made of parabolic dish and horn at the focal point. There are many different configurations with the placement of horn antenna. One such most popular arrangement is shown in the fig-1. As shown waveguide is used to feed the horn placed at the focal point. Parabolic dish is curved around the horn which acts as reflector.

reflector antenna
Fig.1 Simple reflector antenna

The most popular method of feeding in the parabolic antenna is to place second reflector positioning at the focal point in place of horn. The position of the horn is changed to the center of the bigger parabolic disc.

cassegrain feed antenna
Fig.2 Cassegrain Feed antenna

As shown in the fig.2 during transmission, EM radiation from the horn transmitted towards small reflector first. The smaller reflector reflects energy towards larger dish. The large dish radiates signal in the parallel beams. This arrangement is referred as cassegrain feed.

Advantages of Cassegrain feed

Following are advantages of cassegrain feed:
•  Waveguide line is short.
•  Radial bends in the waveguide are no longer needed.
•  Due to above the cassegrain arrangement leads to less attenuation and improvement in the noise figure.

The larger Earth station antenna use the cassegrain feed type of arrangement.

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