"Joel Kolstad" wrote in message
...
I've been reading Wes Hayward's articles on coupled resonator filters, and
I've simulated some of the results and they're what I'd expect. However,
his examples are all bandpass filters... and I need a bandstop filter.
Chanigng the parallel LC shunt resonators to series LC series resonators
doesn't really work at all... although there's a perfect notch at the
desired center frequency, the passband response is very low (tens of dB
insertion loss) and recovers very, very slowly. It seemed as though I
just needed a different size coupling capacitor, but playing around some
doesn't improve the response significantly (for instance, if you take the
example on page 85 of Introduction to Radio Frequency Design and change
the parallel resonators to series resonators, even if you change the 7.2pF
top coupling capacitor to something astronomical such as 1nF the response
is still poor).

I've ordered a copy of Zverev's book (and Zverev w/Mathei), where the
theory of all this comes from, but in the interim... can anyone suggest
what the fundamental problem might be? Interesting, from looking at a few
pages of Zverev on Amazon.Com he does have schematics of what I think I'm
after (top capacitor coupled series resonators to create bandstop
filters).

The Elsie filter synthesis program has a bandstop filter design option. I
just tried it and it works OK. None of the designs are top-coupled
resonators, though.

Leon
--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller