Common parabolic Satellite Rx antenna consists of reflector, feed and support poles. According to the different antenna structure, that is to say, the different relative position between the reflector and feed of the antenna, we can classify the parabolic antenna as three different kinds of feed forward Rx antenna, feed back Rx antenna, offset Rx antenna. As shown in Fig.2-1

Feedforward antenna is also called centre focus antenna or Prime focus antenna, what is we often call "big pan". Feed locates the focus point of the parabolic antenna, Satellite signals are reflected by the antenna parabolic surface, and then these signals are focused on the feed. Generally feedforward antennas present roundness, and some present squareness, whose structures are simple. For this kind of antenna, it is convenient to do the installation and adjust the feed, so generally the diameter is within 4 meter. The diameter of common roundness feedforward Rx antenna is 1.0m,1.2m,1.35m,1.5m,1.65m,1.8m,2.1m,2.4m,3.7m,4.2m,and so on, which are often used for C-band signals.

According to the antenna fixing types, roundness feedforward Rx antenna is classified into two types, which are ground mount type and kingpost type. As shown in Fig.2-2.

Feed back antenna belongs to twice-reflected antenna, there're two reflectors, and the main reflector is paraboloid. On the focus point there is a sub-reflector, which is used for reflecting the Satellite signal once again and through the waveguide tube the signal is transmitted to the LNB at the back of the antenna. The main purpose for adopting feed back antenna is to enhance the antenna receiving efficiency and improve VSWR. The highest efficiency of feed back antenna can be getting to 75%, but the highest efficiency of common antenna just can be getting to 70%. Additionally, if the user adopts feed back antenna, LNB can avoid to be affected by high temperature in the hot area; however, the structure of feed back antenna is complex and also the production cost is much higher, so generally for bigger diameter antenna, it will adopt feed back structure so as to be convenient to do the feed assembly and adjustment; and for individual receiving, feed back structure will not be used.

According to the sub-reflector shape, feed back antenna can be classified into two kinds, one is Cassegrain antenna, and another one is Gregory antenna.

(1) Cassegrain antenna

The sub-reflector of Cassegrain antenna shows hyperboloid of revolution, and the Casegrain antenna is often used for commercial earth station. As shown in Fig.2-3

A part of feedforward and feedback antenna is adopted in offset antenna; its feed and sub-reflector are deviated from the right ahead of the reflector, which can not stop the Satellite signal, so the efficiency is high, as shown in Fig.2-5. Most offset antenna reflector shows ellipse shape or die rhombus, this antenna is often used for receiving ku band signal.

There are two kinds of offset antenna, one is once-reflected antenna, and another one is twice-reflected antenna, once-reflected antenna is the common offset antenna, as shown in Fig.2-6, also called dish antenna. Its structure is simple and cost is low, generally it is used for single Satellite receiving. Common offset antenna reflector is ellipse shape, and the diameter is 0.35m,0.45m,0.55m,0.60m,0.75m,0.85m,0.90m,1.2m,1.5m,1.8m, and so on.

Twice-reflected antenna belong to multi-curved surface antenna(multi-focus antenna), as shown in Fig.2-7, its reflector use denatured spherical surface or poraboloid, like the rectangle cut from the spherical surface, or organize the reflector by two kinds of curves, where the horizontal direction is circular arc, and vertical direction is a part of paraboloid. Thus on the antenna many feeds can be installed, and the Satellite signals can be reflected into many feeds which locates on different places, each feed can receive different Satellite signals, and so receiving different Satellites signals from one set of antenna will be realized.