TABLE OF CONTENTS A signal traveling between an earth station and a satellite must pass through the earth s atmosphere, including the ionosphere, as shown in Fig. 4.1, and this can introduce certain impairments, which are summarized in Table 4.1. Some of the more important of these impairments will be described in this chapter.
| Propagation impairment | Physical cause | Prime importance |
|---|---|---|
| Attenuation and sky noise increases | Atmospheric gases, cloud, rain | Frequencies above about 10 GHz |
| Signal depolarization | Rain, ice crystals | Dual-polarization systems at C and Ku bands (depends on system configuration) |
| Refraction, atmospheric multipath | Atmospheric gases | Communication and tracking at low elevation angles |
| Signal scintillations | Tropospheric and ionospheric refractivity fluctuations | Tropospheric at frequencies above 10 GHz and low-elevation angles; ionospheric at frequencies below 10 GHz |
| Reflection multipath, blockage | Earth s surface, objects on surface | Mobile satellite services |
| Propagation delays, variations | Troposphere, ionosphere | Precise timing and location systems; time division multiple access (TDMA) systems |
| Intersystem interference | Ducting, scatter, diffraction | Mainly C band at present; rain scatter may be significant at higher frequencies |
| SOURCE: Brussard and Rogers, 1990. |
Losses occur in the earth s atmosphere as a result of energy absorption by the atmospheric gases. These losses are treated quite separately from those which result from adverse weather conditions, which of course are also atmospheric losses. To distinguish between these, the weather-related losses are referred to as atmospheric attenuation
