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Hot S22 Measurements on GSM PA

Question asked by rajsodhi Employee on Nov 25, 2009
Latest reply on Jan 26, 2010 by Dr_joel

We are working on GSM/GPRS PA's, and we would like to measure 2 port hot S-parameters.  In our lab, we have a N5242a. 

Since we are very sensitive to the idea of putting too much power to the test equipment, we often add a 10 dB pad at the output of the PA.  Our PNA-X can handle 30 dBm, and the maximum power would only be about 35 dBm at room temperature and nominal supply. 

Question #1)  is the receiver attenuation equivalent to an external pad?  could I equivalently just dial in 10 dB of receiver attenuation to protect the front end? 

We often measure Hot-S21, where we put a large single (3 dBm) tone combined with a small signal tone that is sweeping from 500 MHz to 3 GHz.  To do this, we use an enhanced response Cal.   Finding it is labyrinthine, but here's the procedure that we use.
Calibration - start Cal - Cal Wizard - Smart Cal (uses mechanical standards)
(brief aside: this menu pick is rather misleading, since we can use the e-cal module based on the connectors we choose)
2-port Cal (1,4) - APC 3.5 female - then choose the e-cal module
check the modify box, and under thru Cal method, select e-cal defined thru.
Cal Type = enhanced resp 4 <= 1
ok -> next -> measure.

Attached, please find our path configuration.

Question #2) my measurement of S44 is terrible, because I'm measuring through 20-60 dB of attenuation, depending upon how much receiver attenuation I add.  How can I get reflection coefficient at the output port of the PA under bias and under power?  Is there a step-by-step set of instructions or an application note?