Beam-spreading Loss

In satellite communications, beam-spreading loss results from the spreading of the Earth-satellite signals as they pass through the Earth’s troposphere. The atmosphere does not have a constant refractive index profile so that it acts like a diverging lens and spreads the transmitter’s beam to reduce the signal strength at the receiver. Beam-spreading loss is not a major loss and can be averaged over the year to be approximately 1.1 dB for the worst elevation of 0°. While it can be ignored for elevations above 6°, losses can reach several dB for elevations less than 6° at latitudes above 50°. For low angles, the refractive index profile of the troposphere results in the wave being bent toward the Earth, resulting in additional losses. Again, the loss is only significant for high latitudes and low elevations.