1. Introduction
The payload is made up of a repeater and antenna system. The repeater (transponder) performs the required processing of the received signal and the antenna system is used to receive signals from LES and to transmit signals back to MES in the coverage area and vice versa.
2. Satellite Repeaters
The function of a repeater is to receive the uplink RF signals from either ground segment service or feeder links, to convert these signals to the appropriate downlink frequency and power and to retransmit them towards the service or feeder links ground segment. Thus, two types of repeater architecture are possible in on-board utilization of communication satellites: Transparent or Bent-pipe, and Regenerative transponders.
1. Transparent (Bent-pipe) Transponder – The basic function of the satellite transponder is to isolate individual carriers or groups of carriers of signals and to boost their power level before they are retransmitted to the ground stations. At this point, the carrier frequencies are also altered as the carriers pass through the satellite. Satellite repeaters that process the carrier in this way are typically referred to as transparent or bentpipe transponders, shown in Figure 1. (A). Only the basic RF characteristics of the carrier (amplitude and frequency) are altered by the satellite.