"Tom Bruhns" wrote in message
m...
Another issue you'll have to deal with if you don't do some scaling of
some sort is that the inductors that go with the fractional-pF
capacitors will have significant parasitic capacitance...you're likely
going to get self-resonant frequencies not far above the filter
stopband frequency (or worse).

Yes, I can definitely appreciate that.

It would help a lot if you could make
the filter stopband considerably wider. Seems like with a 10MHz
stopband, you're asking for filter performance not too unlike a
duplexer.

Well, it's supposed to be an adjustable notch filter, from 30-500MHz, with a
2% stopband width... and it's at the high end where it's looking pretty
challenging.

You mentioned the need for the filter to be flat down to low
frequencies, but what about higher frequencies? Are the repetitions
which are common in distributed (transmission-line) filters really a
problem?

At the higher frequencies, no. At lower frequency, yes! This might suggest
breaking it up into two filter, since I could probably get 300-500MHz out of
distributed filter. The problem there is how to set the center frequency...
although simply using PIN diodes or similar to ground the transmission line
somewhere along its length sounds promising.

---Joel