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Positive S11 measurement on a filter??

Question asked by damen78 on Feb 17, 2011
Latest reply on Apr 6, 2011 by daras
Hi.. I'm using a E5071C ENA Analzyer...Here's the problem I have:  I'm trying to measure S11 of a connectorized 1GHz LP filter.  I did a full 2-port cal using mechanical precision standards (load and short).  When I measure the filter... the S11 curve goes into the positive region in the stop band (between 3.7 to 5.3GHz).  This means I'm getting back more signal than is being transmitted right??  I don't understand that because it's a passive device.  Now when i do a Response cal... like say Response(open) with the load option... I get a measurement that is more beleivealbe: no positive S11.  I've tried other filters and have had the same results.  I've tried using other ports.. same results.  I've tried doing the 1-port cal... same results... the only thing that seems to give a resonalbe answer is when i do a Response cal.  Does anybody know what i may be doing wrong?

I'm not an advanced network analyzer user... but measuring a filter should be easy.. right??
Thanks for your time.