Communications satellite service S (2~4 GHz) 2.31~2.37 Digital Audio Radio Service 2.0~2.2 MSS MSS, mobile satellite services. and devices active in radio frequency ranges. Signals in the K bands exhibit a higher path loss and fading in the presence of rain. However, K band systems can operate with smaller size antennas. Most present day satellites are designed to operate in both C and K bands, where the C band is used for wide geographic coverage and the K band for regional coverage. The K band satellites are being rolled out to provide broadband internet coverage on a global basis. Satellite Communications Antennas A range of different antennas are used for satellite communications. Early systems required the signal power to be much larger than noise power as the quality of analogue voice and video communications reception would be greatly impacted. Powerful antennas were used on the ground at earth stations to communicate with satellites. These antennas have gains in the order of 60 dB, that is, they can boost the received power by 106 times. Because of their size, and also to reduce the amount of background noise, these antennas were usually constructed far away from cities and generally in rural areas. The earth station antenna, used by OTC (one of the companies which formed Telstra Ltd) to communicate with an Intelsat satellite is shown in Figure 11.3. It is reported that in 1984 half of Australia's international telephone traffic passed through this antenna [7]. Antennas on board the satellite were generally of a smaller size and gain because of launch logistic limitations. One or more reflectors receive and transmit signals to Earth via a feed array which enables the satellite to focus communications on a particular spot on Earth. A typ- ical footprint of a satellite operating over the Indian Ocean is shown in Figure 11.4. Usually the broader coverage uses the C band and the more localised, country-level coverage operation uses the K band. The transmitted power from the satellite transponder is amplified 