Satellite dish antenna

Satellite dish antenna is used to capture signals coming from the communication satellites and transmit these signals to the TV/radio sets of the user after converting these signals into compatible waves which can be interpreted by the sets. The satellite dish antenna contains an active and a passive element. The parabolic reflector surface is the passive element as it reflects the microwaves sent from the communication satellites on to the active element- waveguide.
The passive part i.e. the reflector of the satellite dish antenna has a diameter which is many times the wavelength of the incoming electromagnetic (or micro waves). In fact the diameter of the dish depends upon the wavelength of the signal. If the wavelength which the dish receives increases, the diameter of the dish also has to be increased. Also, a geometrical property of a parabola is used in its design. Parabolic surfaces reflect all the waves coming along its axis on its focal point. This property helps in focusing all the weak signals on a small point where the active element of the antenna is placed.
The active element has to perform two functions of the satellite dish antenna. The reflected beams are received by this element which is known as the feedhorn (front part of the waveguide). The feedhorn, along with the low noise block converter known as LNB, converts these electromagnetic waves into electrical signals. Also the signal is amplified. Secondly, the system try to reduce the noise which otherwise would create hindrance in the transmission.
The noise is reduced in the system by the LNB converter. If it is not done then the noise may get amplified in the subsequent stages and it will interfere in the normal functioning of the system. The transmitted signals are fed into the feeders which are very long running into meters. In case the LNB is not used, the signals that reach the sets are very weak. In presence of active element, since the signal is amplified and the noise is reduced, this leads to better transmission and sets receives a stronger signal.
The satellite dish antenna specification is designed keeping in mind the following parameters- the path loss, receiver sensitivity, signal to noise ratio, transmitter power levels, theoretical gain required etc. The theoretical gain is given by the following formula
G=
Where G is the theoretical gain
D is the reflector diameter in same unit as wavelength
? is the wavelength of the signal
However, the practical considerations when taken into account reduce this theoretical gain by 40-45% and the actual gain obtained is 55-60% of the theoretical gain.