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| Adjusting of coupled filters with a VNA |
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| DeepLink:
Hi Need to adjust some coupled filters, (3 to 5 poles - below 500MHz) Having read the app note 1287-8 from HP, it seems that "Time Domain Analysis" is the way to go I do have HP 8714ES w. opt. 100 Siglent SVA1032X w. DTF None of these VNA's offer real Time Domain Analysis, but are the DTF options any good for adjusting filters? I can't afford a E5071 or other fancy equipment, so I'm looking for a way to do it with what I have now, or the next step up Maybe a HP 8753* with opt. 010? How are you adjusting coupled filters? |
| S57UUU:
I guess these are bandpasses? You can tune them in frequency domain, with a normal network analyzer (even a scalar one). Measure S11 (do not forget a load at port 2). Tune all of the resonators way off (or short them). Do a response calibration (normalization). Tune the first resonator, to get a minimum in S11 at center frequency. At this stage set the scale to 1dB/div or less, since the minimum will be very shallow. You can deepen it by introducing some loss (finger...) into resonator #2. Next, tune resonator #2. Depending on your coupling between the resonators (filter width), the minimum will split into two, or just become deeper. If split, tune #2 so, that the two dips are symmetrical around center frequency. Tune #3 to get three symmetrical dips, etc. Marko Cebokli |
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