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A question about AN "Accurate Absolute Power Measurements ... "

Question asked by b.d.hall on Mar 16, 2013
Latest reply on Mar 26, 2013 by tabbott
I have a question about the N5531S Application Note +"Accurate Absolute and Relative Power Measurements Using the Agilent N5531S  Measuring Receiver System"+.

I would like to better understand Appendix A, which looks at the absolute power accuracy. But my question is really about how the N5532A sensor module is calibrated. 

Now on page 5 of the AN, it says that the N5532A is calibrated as a unit, by terminating the RF output port with a load and characterizing the unit as +"... if it were a regular power sensor"+.

So, is calibration of the N5532A in this way preferred? The alternative would be to remove the power sensor from the unit, calibrate it separately and then reassemble everything.

My guess is that disassembling the unit is not recommended, but perhaps I am wrong. Appendix A appears to suggest otherwise. Pages 13 and 14 describe the detailed measurement equations required for an uncertainty analysis. They include mismatch terms at internal N5532A interfaces (e.g., between splitter output and power sensor input) that would only contribute to uncertainty if the power sensor was characterized independently (otherwise the effect of these interfaces is included in the composite calibration factor).

So, I would be grateful if you could clarify the preferred method of calibrating the N5532A.

Also, if anyone is able to shine some light on the second to last paragraph in Appendix C I would be grateful. It says there

+"... This situation is equivalent to the situation under which they were calibrated. Thus they are both, simultaneously optimally accurate as configured with a two-resistor splitter. ..."+

This phrase seems to say that calibration of the power sensor is done in-situ. But I don't see why the situation would be any different if a divider had been chosen.

Thanks in advance  :-)