Ask Dr. SETI ®
I am working with multipole stripline bandpass filters and have the following questions. The 1/2 wave lines are u shaped instead of just straight.
The Doctor Responds:
The physical dimensions are a function of the desired insertion loss, skirt selectivity, and passband ripple. They are also determined by the selected filter topoplgy (the two most popular being Tchebycheff and Butterworth, giving rise to the old EE's riddle, "What's butterworth to tchebycheff?")
Most of us use microwave CAD software to design these filters. I favor EagleWare, although EEsof (a division of Hewlett-Packard) and Super-Compact are also good. Problem is, these packages run $5k to $10k. ARRL Radio Designer is a stripped-down version of Compact, for $150, but I don't think it does microstrip filters.
The real experts on hairpin filters are Rick Campbell KK7B and Jim Davey WA8NLC. They wrote the pivotal series of articles on the subject in QST and QEX, and designed the famous no-tune transverters which are now manufactured by DownEast Microwave. They also wrote a bunch of papers for various microwave and VHF conference proceedings. I have these indexed on this Web site, at http://www.setileague.org/articles/proceed.htm.
The filter relationships are especially complex, and unless you have access to the appropriate design software, this may well be an area in which it makes sense to scale from an existing design.
As for GaAs FET amplifier matching, Kent Britain WA5VJB and Al Ward WB5LUA are the acknowledged experts. Look for their calls in the above-referenced Proceedings indices. Some of my own 73, Ham Radio, QST and QEX articles may be useful here as well. For a complete listing of my publications, see: http://www.setileague.org/admin/publicat.htm.
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this page last updated 28 December 2002
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