Antimetrical Case
A similar simplification can be made for lossless antimetrical filters. In this case the substitution
is made into the general equation. For the passband,
and for the stopband,
Antimetrical, in this context, means that the filter image impedances and terminations at each end are the dual of each other. This will be the case if the filter has a series and shunt section of the same type, respectively, at each end. Symmetrical filters have an even number of half-sections and antimetrical filters have an odd number of half-sections. In the vast majority of cases the filter design will be either symmetrical or antimetrical and one of these reduced expressions will apply.
Read more about this topic: Image Filter End Terminations
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