Passband ripple is more a function of the filter design parameters--was
it designed as a Chebyshev with 1 dB passband ripple, or a Butterworth
with a flat passband, or a Gaussian with a rounded passband, etc. And,
of course, those parameters govern also how fast the skirts roll off
and, of great importance in many applications, how the group delay looks.
All else being equal (e.g., two filters, same nominal 3 dB bandwidth,
same design parameter, e.g., Chebyshev) the one with more poles will
have better passband roll off, or shape factor.
I can show you some four pole crystal filters I've designed and built
with essentially perfectly flat passbands and others with lumpy passbands.
Jack K8ZOA
Fred (FL) wrote:
If my CAD computer design days don't fail me, I recall
8-pole type filters - had much steeper skirts, but
not so hot passbands, sort of ripply. Having already
forgotten the spec on group-delay (phase?) - I'll
have to look that up.
Fred, N3CSY
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