A transponder is a device on a satellite that receives transmitted signals from an Earth station on an uplink frequency, amplifies the signals, and retransmits them on a downlink frequency to Earth. It functions as both a repeater and a frequency converter in space. Transponders are classified as either nonregenerative or regenerative. Nonregenerative transponders only alter the signal's amplitude and frequency, while regenerative transponders also alter the received signal before demodulation to offer flexibility in optimizing transmission link performance.

1. Transponder
Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
Course: MCE203A
4/23/2020 1Arpan Deyasi, RCCIIT, MCE203A

2. What is
transponder?
It is a repeater which
• receives transmitted signal from Earth station on uplink
• amplifies it
• retransmits it on downlink at a different frequency
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3. Transponder = Transmitter + Responder
Functions
1. Repeater in space
2. Frequency converter
3. Isolating neighboring RF channels
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4. Duplexer is a
two-way
microwave gate
which receives
uplink signal from
satellite antenna
and transmits
downlink signal to
the satellite
antenna
Low Noise Amplifier (LNA)
amplifies the weak received signal
Carrier Processor performs
the frequency down
conversion of received signal
(uplink). This block
determines the type of
transponder.
PowerAmplifier amplifies the
power of frequency down
converted signal (down link) to the
required level.
4/23/2020 4Arpan Deyasi, RCCIIT, MCE203A
Satellite
Antenna Duplexer
Low Noise
amplifier
Carrier
processor
Power
amplifie
r

5. Classification
Transparent/
Nonregenerative/
Bent pipe
Regenerative
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6. Nonregenerative Transponder
.processes uplink signal
by altering amplitude
and frequency
.works as
frequency
converter
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7. Nonregenerative Transponder
uplink section consists of input filter, LNA, down-converter,
local oscillator
downlink section consists of input multiplexer, power
amplifier, output demultiplexer
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8. Nonregenerative Transponder
Full bandwidth is separated by individual transponder
channels by input MUX
Each IMUX is tuned to pass the full bandwidth of a
particular channel and reject other channels
Output of each IMUX is amplified by separate
power amplifiers
Output of all transponder channels is then combined
by output DEMUX
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9. Regenerative Transponder
.received signal is also
altered before demodulation
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10. Regenerative Transponder
Functions
1. uplink demodulation
2. error correction
3. downlink re-modulation, amplification, transmission
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11. Functional difference
Nonregenerative transponders can’t be used to reduce link
noise, optimize transmission link
Regenerative transponders can offer the flexibility of
performance optimization as they employ demodulation
technique
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12. References
https://www.slideshare.net/AbhishekDutta62/transponder-67142678
https://www.tutorialspoint.com/satellite_communication/satellite_
communication_transponders.htm
T. Pratt, C. Bostian, J. Allnutt, “Satellite Communications”, John
Wiley & Sons, 2nd Ed., 2003
A. K. Maini, V. Agarawal, “Satellite Communications”, Wiley, 1st Ed.,
2019
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