Pass-Band VSWR of Maximally Flat Band-Pass Filters (Correspondence)

Microwave band-pass filters using high-Q cavity resonators can often be designed for almost negligible midband dissipation losses (i.e., <1/2 db). If these filters are designed for a maximally flat amplitude response, the insertion loss within the pass band is approximately equal to the reflection loss within the pass band. Then R = 10 log (1 + X²ⁿ), where R = reflection loss in db X = normalized frequency variable n = number of cavity resonators.