Friday, 10 July 2015

Cassegrain antenna

Cassegrain antenna

Cassegrain antenna is another commonly used in microwave communication antennas, which evolved from a parabola. Cassegrain antenna consists of three parts, namely the main reflector, sub-reflector and the radiation source. In which a rotating parabolic main reflector, sub-reflector surface of the rotational hyperboloid. Structurally, the focus of a hyperbolic paraboloid focus coincides hyperboloid focal axis coincides with the axis paraboloid focus, and the focus of the radiation source is located on another double curved, as shown below. It was a reflection of the electromagnetic radiation emitted subreflector carried out, the electromagnetic wave reflection to the main reflector, and then after the main reflector reflected plane wave beam obtain directions to achieve directional transmission. Cassegrain antenna works as follows.

When the radiator located hyperboloid of revolution real focal point F1, the rays emitted from F1 after the reflected rays hyperboloid, the equivalent of the virtual focus hyperboloid emitted directly out of the rays. So as long as the focus of the hyperboloid virtual focus coincides with the paraboloid, the sub-reflecting surface can be the main ray reflecting surface is parabolic reflector in a plane wave radiated.

Cassegrain antenna with respect to a parabolic antenna is concerned, it will feed the radiation pattern from the feedforward parabolic manner changed after the feeding mode, which makes the structure of the antenna is more compact, making it more convenient. Also Cassegrain antenna is equivalent to a parabolic antenna with a long focal length, and this can be a long focal length to the distance from the antenna from the focal point of each aperture is nearly constant, thus space radiation attenuation effect on the feeder to be smaller so Cassegrain antenna efficiency is higher than the standard parabolic antenna.