Why is rain attenuation in satellite communication?

Answer 1

Any satellite communications system network operator using a Ku-Band system (12/14 GHz or higher frequencies) will face the effects of rain fade at some time. But to understand why this weakening occurs with Ku-Band transmissions, you must first understand the causes of satellite rain fade. Two of the most common causes are listed below.

• Absorption - Part or all of the energy generated when a radio wave strikes a rain droplet. The droplet is converted to heat energy and absorbed by the droplet.
• Scattering - A non-uniform transmission medium (the raindrops in the atmosphere) causes energy to be dispersed from its initial travel direction.

Scattering can be caused by either refraction or diffraction:

• Refraction - The refractive index of the water droplets encountered by the radio wave.
• Diffraction - the travel direction of the radio wave also changes as it propagates around the obstacle in its path (a water droplet).

It refers primarily to the absorption of a microwave Radio Frequency (RF) signal by atmospheric rain, snow or ice, and losses are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a storm front. Rain attenuation or fade can be caused by precipitation at the uplink or downlink location. However, it does not need to be raining at a location for it to be affected by rain fade, as the signal may pass through precipitation many miles away, especially if the satellite dish has a low look angle.

From 5 to 20 percent of rain fade or satellite signal attenuation may also be caused by rain, snow or ice on the uplink or downlink antenna reflector, radome or feed horn.

Answer 2

Any satellite communications system network operator using a Ku-Band system (12/14 GHz or higher frequencies) will face the effects of rain fade at some time. But to understand why this weakening occurs with Ku-Band transmissions, you must first understand the causes of satellite rain fade. Two of the most common causes are listed below.

• Absorption - Part or all of the energy generated when a radio wave strikes a rain droplet. The droplet is converted to heat energy and absorbed by the droplet.
• Scattering - A non-uniform transmission medium (the raindrops in the atmosphere) causes energy to be dispersed from its initial travel direction.

Scattering can be caused by either refraction or diffraction:

• Refraction - The refractive index of the water droplets encountered by the radio wave.
• Diffraction - the travel direction of the radio wave also changes as it propagates around the obstacle in its path (a water droplet).

These different reactions ultimately have the same effect - they cause any satellite system to lose some of its normal signal level. Don't expect to lose your satellite signal every time it rains, though. Rain outage will only occur during the heaviest rains (convective and stratiform are the most predominant types) with only a small portion of the transmission path experiencing attenuation. In fact, of a typical satellite transmission path measuring 22,300 miles, less than .02% will be affected by rain fade.