SAW filter characterization...

Andi <timewontw8@...>



First, let me compliment you on the wonderful job you did on the mini VNA Tiny.  I use it for all sorts of stuff and I am very happy with it.  Recently, I tried to measure a 140MHzX5MHz SAW filter on it and got some pretty strange results.  First, I calibrated using method 1 and a SOLT at the reference plane of the filter.  Next, the match was so bad the entire filter was on the edge of the Smith Chart.  So, I added a 0603 100nH series inductor immediately in front of the filter and got a decent reading.  Then I backed out the series inductor's impedance to arrive at what I thought would be the SAW filter's actual impedance.  I then repeated the above procedure with a 47nH inductor.  This time, I backed out an entirely different SAW filter impedance.  I expected the two impedances to be similar but they were not.  Any idea what may have gone wrong?


--Andy Robertson



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