AnsweredAssumed Answered

Source port unleveled after calibration

Question asked by engineer007 on Mar 22, 2013
Latest reply on May 21, 2013 by daras

I have a problem here that I don't understand.

I'm now working on a test system for a high power amplifier using PNA N5222A.

I'm basically measuring all the typical parameters for an amplifier such as S-parameters, gain linearity (power sweep) and so on.

Because the amplifier has a very high gain, I have a very big attenuator (of 40 dB) connected to the amplifier output before it is connected to Port 2. 

The setup is very basic with Port 1 connected to amplifier input and amplifier output connected to the attenuator and the attenuator connected to Port 2.

Before test, I calibrated the PNA with the attenuator in place. I used Cal All wizard (because I have setup several channels of measurements i.e. several power sweeps at different frequencies). 

However after calibration, the PNA complained that the "Source unleveled".

Because of this, I did the following for troubleshooting:-
1. Calibrated PNA without attenuator, works fine without source unleveled error.
2. Calibrated PNA with a smaller value attenuator of 10 dB, the measurement worked fine also without error.
3. But once I increased the attenuator pad to 20 dB, the error appeared again after calibration.

The power sweep that I set is from -30 dBm to 0 dBm, well below what is permitted, so I was wondering what went wrong.

Are there special settings that I need to do in order to cal the PNA that is connected with a high value attenuator (40 dB)?