This question appears in Mumbai University > Satellite Communication and Network subject

Marks: 8 M

Year: May 2015

A signal traveling between an earth station and a satellite must pass through the earth’s atmosphere, including the ionosphere, and this can introduce certain impairments, which are summarized in the table below.

Propagation impairments have a significant impact only for less than one percent of the time during a year, so the system gain must be enhanced through an additional fade margin carefully estimated to satisfy the desired availability and QoS specifications.

Propagation concerns for Satellite Communications Systems

Effect on Ku band –

When propagating through rain, snow, hail, or ice droplets, radio waves suffer from power loss due to hydrometeor scattering.

Although hydrometeor scattering is the major limiting factor in the EHF band (>30 GHz), hydrometeor absorption is the dominant phenomenon causing power loss in the lower spectral part between 10GHz and 30GHz. The combined effect of hydrometeor scattering and absorption results in a power loss proportional in dB to the square of the frequency. This constitutes the main disadvantage of operating at the Ku, Ka, or V frequency bands. As far as satellite systems are concerned, the depth of rain fades also depends on the elevation and polarization angles. On the other hand, as rain attenuation depends unfavourably on the rainfall rate and the raindrop size distribution, it affects heavily tropical and subtropical regions.

Effect on C band –

As tabulated propagation impairments have affects like scattering and diffraction in lower frequencies like that in C band. Rain and ice crystals may lead to signal depolarization which can again affect the reception of satellite signals by Earth stations.