A 'Hot' S22 measurement is a normal S22 measurement of a power amplifier with drive power applied to the amplifier input. This situation more closely resembles the output match characteristics of an amplifier under normal operating conditions.
On the PNA-X:
Press Meas, then Measurement Class, then Standard. Click OK.
Press Freq, then set the Start and Stop frequencies for the measurement.
Press Frequency Offset. Enable FOM and set the Source(1) frequencies with a positive or negative offset of at least (100 * IFBW). This will be the Hot (Input) signal and must be far enough away from the S-parameter frequencies to avoid interference.
Click Stimulus, then Sweep, then Sweep Setup. Check Stepped Sweep.
then Channel, then Hardware Setup, then Path
Under Configuration select Hot S-Parameters.
Configure the rear-panel cables as shown in the above Path Configuration diagram:
On the rear panel, connect 'SRC2 SW SRC OUT (J8)' to Port 1 'COMB THRU IN (J10)'
Connect Port 1 'SW SRC OUT (J11)' to Port 1 'COMB THRU IN (J9)'.
Connect DUT input port to PNA port 1
Connect DUT output port to PNA port 2."
The 'Hot' (input) signal coming from Source 2 is routed through the coupled arm of the combiner to port 1 and the DUT input.
The S-parameter (S22) signal coming from Source 1 is sent directly to Port 2 and the DUT output.
Press Power, then Power and Attenuator.
For Port 2 (DUT output) select at least 10 dB of source attenuation on the Source 1 path.
For Port 1 (DUT input) select the S-parameter port power level.
Set Port 1 Src2 and Port 3 to OFF.
Click Receiver Attenuator. Considering the gain of the DUT and the Source 2 input power, select the appropriate attenuation for the B receiver.
Perform a 2-port Calibration
Connect the DUT and measure S22. To ensure the DUT is being driven and the desired power level, perform a Source Power cal for Port 1 Src2.
In the Power and Attenuator dialog, adjust the Port 1 Src 2 power level and notice the change in S22.
The following image shows a Hot S22 measurement of a Hittite HMC452ST89 Power Amp tuned for 900 MHz.
The Red circled measurement is Hot S22.
The other is with the Hot signal OFF.
If the Hot signal is too close to the measurement signal, ripples appear on the out-of-band region of the trace.