"Paul Keinanen" wrote in message
The OP clearly had something similar in mind

Yes, that was my plan.

since he originally
asked for a 2:1 tuning range, but now he is asking for the 30-500 MHz
range. I do not think that such huge range can be handled by just
switching base capacitors. With such large frequency range, it would
make more sense, to build at least three completely independent
filters, say 30-90 MHz, 90-270 MHz and 270-500 MHz, while each filter
could switch in base capacitances.

I was thinking of two... 30-125MHz and 125-500MHz. I.e., each one tunes a
range of about 4:1. Something like 3-5 base capacitors would provide the
broad tuning, with varactors doing the fine tuning.

The two lower filters could be
lumped LC filters, while the last range could be limited to less than
one octave, so that strip line filters could be used.

The problem is that even though the 125-500MHz filter only needs to create a
bandstop region somewhere in the 125-500MHz range, it must otherwise still
pass the complete 30-500MHz range. As far as I can tell, this still
eliminates all distributed-style filters from consideration.

---Joel