Transponder (Satellite communications)
Overview
Communications satellite
A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...
’s transponder, is the series of interconnected units which form a communications channel between the receiving and the transmitting antennas .
A transponder is typically composed of:
- An input band limiting device (a band pass filter)
- An Input low-noise amplifierLow-noise amplifierLow-noise amplifier is an electronic amplifier used to amplify possibly very weak signals . It is usually located very close to the detection device to reduce losses in the feedline. This active antenna arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is...
(LNA), designed to amplify the (normally very weak, because of the large distances involved) signals received from the earth station - A frequency translator (normally composed of an oscillator and a frequency mixerFrequency mixerIn electronics a mixer or frequency mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals at frequencies f1 and f2 are applied to a mixer, and it produces new signals at the sum f1 + f2 and difference f1 -...
) used to convert the frequency of the received signal to the frequency required for the transmitted signal - An output band pass filter
- A power amplifier (this can be a traveling-wave tube or a solid state amplifier)
Most communication satellites are radio relay
Radio relay
Radio stations that cannot communicate directly due to distance, terrain or other difficulties sometimes use an intermediate radio relay station to relay the signals. Examples include airborne radio relay, microwave radio relay, and communications satellite...
stations in orbit, and carry dozens of transponders, each with a bandwidth of tens of megahertz.
