Abstract: Method and apparatus for performance characterization of Ka band transponders wherein measurements are made. A wideband modulated data signal is used to test the response of the Ka band transponder. A periodic test pattern, preferably a pseudo-noise (PN) sequence, modulated on a carrier, is transmitted to an onboard satellite transponder which then retransmits the signal to a receiver where a down converter is used to output inphase and quadrature phase baseband signals which are digitized and used for measuring one or more of the following: Magnitude and phase response AM/AM and AM/PM Phase noise Bit error rate Data asymmetry I/Q channel imbalance.