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Device affected by self-heating

Question asked by augusto on Jul 28, 2011
Latest reply on Jul 29, 2011 by augusto
Hello everybody,

   I am new on this nice forum, and I would like to ask you a question on the S-parameters measurement of a device that does not reach a steady state because of self-heating effects.
I am using an Agilent N5230A, 4 ports, 20 GHz, VNA and I observed a strong dependance of the device response with the IF bandwidth. The behavior is in good agreement with the theory: smaller the IF B.W., longer the time spent at each (frequency) point, higher the self-heating effect, stronger the change of the device impedance. Very good, but my question is: how does the VNA measure a device that is changing its impedance over the measurement time? Is the measurement an average of the S-parameters values in the time-window defined by the IF B.W., or there is some other effect?

Thank you very much in advance for any hint! Have a good day,