Transponder

A satellite transponder is the core communications payload component. It receives an uplink signal from Earth, amplifies it, changes its frequency (to avoid interference with the much stronger uplink), and retransmits it back to a different ground location or coverage area. Communications satellites carry multiple transponders — from 12 to 100 or more — each operating on a specific frequency channel within a band (typically C-band, Ku-band, or Ka-band). Transponders can be configured as bent pipe (simple amplify-and-retransmit) or regenerative (onboard processing and demodulation). The total transponder capacity of a satellite determines its commercial value. Operators lease transponders by the year, with pricing varying by band, coverage, and power. High-throughput satellites use hundreds of spot beams and frequency reuse to multiply effective transponder capacity.