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).

Thanks,
---Joel Kolstad