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Specifying a BAND PASS FILTER
Fp1 is the Pass Band start frequency. Fp2 is the Pass Band finish frequency. Ao is the flat ( or minimum) loss of the filter. This can very low, a fraction
of a dB or even 0 dB. Ap is the maximum loss in dB in the Pass Band. The
amplitude variation in the Pass Band is the difference between Ap & Ao, and
consists of roll-off & ripple. If there is a ripple constraint that is less than
Ap – Ao, it should be stated.
As is the minimum permissible attenuation in the Stop Bands with respect to Ao,
The Stop Bands extend from Fo to Fs1, and from Fs2 to Fm. The Stop Bands are not
necessarily flat and equal as shown in the above drawing .They can have segments
that have different flat or slope attenuation requirements
The Transition Regions are usually not defined unless constraints are required.
Return Loss in dB over the Pass Band is specified in terms of the minimum
required at the input and output.The higher the Return Loss the better the match
of the filter with the source and load, both usually 50 OHMS unbalanced.
If Group Delay is an issue then the maximum allowable relative parabolic, slope,
and ripple components must be stated.
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