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Specifying a BAND STOP FILTER
The Stop Band extends from Fs1 to Fs2. Fs1 is the start frequency of the Stop
Band. Fs2 is the finish Stop Band frequency. The Pass Bands extend from FP1 to
FP2, and FP3 to FP4.
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 Bands. The
amplitude variation in the Pass Bands 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 Band with respect to Ao,
where the Stop Band begins at Fs1 and extends to Fs2. The Stop Band is not
necessarily flat and equal as shown in the above drawing .It can have segments
that have different flat or slope attenuation requirements
The Transition Region are usually not defined unless constraints are required.
Return Loss in dB over the Pass Bands 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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