Re: BPF too good? #filter


I'd be suspect of the cal.   If the cables and jig called at 20M the loss should
be zero and the SWR  also perfect (cal absorbs errors).

The S11 should be a good match inside the pass band, its a symmetrical

For S21 its too good.  I can imagine and model a better filter loss but
only with perfect caps and coils.  See ELSIE.

1.25Db is best I could ever do for double tuned and that was with
3/8th" ceramic slug tuned inductor ( with enough turns to keep
core barely inserted) with silver mica caps critically coupled.

That was verified with both VNA (agilent 8573) NanoVNA, and
S11/S21 setup on Rigol DSA815T.  I tend to do that want I get
numbers close to the book.  I have found the NanoVNA I have
to be a bit more optimistic at HF by variable amounts but under
.1db (good enough).

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