Outout backoff(OPBO) vs Input Backoff(IPBO) in RF Amplifier

Both the Output backoff(OPBO) and Input Backoff(IPBO) are used to determine the operating power levels required in a satellite transponder TWTA or RF Power Amplifier to function in linear region.

Output Back-Off (OPBO) is the power level at the output of RF amplifier relative to maximum output level possible using the RF amplifier.

EXAMPLE:
Maximum output level = +40dBm
Measured output level of RF Amplifier = +34dBm
Output Backoff(OPBO)= 6dB
Input Back-Off (IPBO) is the power level at the input of RF amplifier relative to input power which produces maximum output power.

Example:
Input power level causes max. output power = -20dBm
Actual input power level = -25dBm
Input backoff(IPBO)= 5dB
OPBO is used even to calculate inter-modulation distortion power levels at the output of TWTA/SSPA. For SSPA output backoff is same as 1dB compression point and for TWTA output backoff is same as saturated output power.

In a satellite link calculation, input backoff is calculated by taking difference between actual flux density and the saturated flux density. Also calculated Output backoff help calculated actual EIRP of the satellite.