Symmetrical Case
Where the filter has symmetrical image impedances and terminations, the expression can be considerably reduced. Note that there is no requirement for the filter to be symmetrical internally, only that the end sections have the same image impedance facing into identical terminating impedances.
A further simplification can be made if there are no resistive losses in the filter (or they are assumed to be negligible). In this case, the image impedance is purely real (RI) in the passband and purely imaginary (iXI) in the stopband. The magnitude of the transfer function is given by
where for the passband,
and for the stopband,
Read more about this topic: Image Filter End Terminations
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