Agilent X-Parameter Generator

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Reference SignalThe Large Signal Operating Point (LSOP) for X-parameters is always defined with onereference signal per fundamental frequency.
In order to enforce time invariance and avoidduplicate measurements, the phase of this reference signal is defined to be zero and isnever swept. A message is displayed on the status window indicating which signal waschosen as the reference signal.

To understand why a reference signal is needed, consider a simple LSOP consisting of onelarge tone at a single frequency.
A large signal AM/AP with magnitude M and phase P issimply a time-delayed version of a large signal AN with magnitude M and phase 0. Timeinvariance principle states that the response to AM/AP should be exactly the same as the time-delayed response to AN, so there is no need to store X-parameters for both sets ofstimulus.
Instead the X-parameters are always measured at phase 0, and the simulationof XnP Components (X1P - X10P) (ccsim) uses time invariance to predict the response tophase-shifted (or time-delayed) signals.
Selection of the reference signal(s) during X-parameter generation and while using X-parameter files with such reference data are both handled internally by the ADS simulatorand requires no input from you.