EIRP (Effective Isotropic Radiated Power) in Satellite Communication 

EIRP (Effective Isotropic Radiated Power) is a term often used in Satellite Communication, also known as Satcom. Isotropic antenna is theoretical one which radiates equally in all directions in a perfect spherical pattern. Gain of antennas are usually mentioned in comparison to the theoretical isotropic antennas as dBi. A dipole antenna has a gain of 2.15 dBi in the direction of the main lobe. EIRP (Effective Isotropic Radiated Power) considers antenna gain, power output of the radio and transmission loss in the cable. Obviously, transmission loss is given a negative value. A simple formula for EIRP would be as follows:
EIRP = Power Output - Cable Loss + Antenna Gain
Cable loss is measured in dB and antenna gain in dBi. Power also has to be in dBW or dBm for this formula. dBW will be power in relation to one watt and dBm power in relation to a milliwatt. Advantage of using dB or deciBel in all calculations is that you can simply add them to get the EIRP when the components are in series like the cable, connectors, diplexer and antenna. If units like Watt or milliWatt are used, calculation involves multiplication. Even though ‘Cable Loss’ is mentioned in the formula, acutally it will include loss in the length of feeder coax used, connectors and diplexer if any.
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