Hot S22 Measurement

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.

Note: Refer also to Active (Hot) Parameters for the latest Hot S22 measurement technique.

Procedure

On the PNA-X:

1. Press Meas > S-Param > Meas Class..., select Standard, then click OK.

2. Press Meas > S-Param > S22.

3. Press Freq, then set the Start and Stop frequencies for the measurement.

4. Press Freq > Main > Frequency Offset.... Enable Frequency Offset and set the Source(2) 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.

5. Press Sweep > Sweep Timing > Sweep Mode to STEPPED.

6. Press Setup > Internal Hardware > RF Path Config....
   

• For PNA-X models N5241B, N5242B, and N5249B: Under Configuration select Hot S-Parameters. This is necessary because these models have different path loss between J9 to Port1 and J10 to Port1 due to the bridge used as a combiner.  The 'Hot' (input) signal coming from Source 2 is routed through the coupled arm of the combiner to port 1 and the DUT input.  Configure the rear-panel cables as shown in the above Path Configuration diagram:

1. 1. On the rear panel, connect 'SRC2 SW SRC OUT (J8)' to Port 1 'COMB THRU IN (J10)'

   2. Connect Port 1 'SW SRC OUT (J11)' to Port 1 'COMB THRU IN (J9)'.

   3. Connect DUT input port to VNA port 1

   4. Connect DUT output port to VNA port 2.

• For PNA-X models N5244B, N5245B, and N5247B: These models use a splitter as a combiner. Set both the Port 1 and Port 3 Bypass Switch to Combiner Path.

7. Press Power > Main > Power and Attenuators.... See Power and Attenuator for more information.

   1. For Port 2 (DUT output) select at least 10 dB of source attenuation on the Source 1 path.

   2. For Port 1 (DUT input) select the S-parameter port power level.

   3. Click Receiver Attenuator.... Considering the gain of the DUT and the Source 2 input power, select the appropriate attenuation for the B receiver.

8. Perform a 2-port Calibration.

9. Press Power, then Power and Attenuator, and set Port 1 Src2 to ON.

10. 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.

11. In the Power and Attenuators 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.