Design of absorptive microwave filters using allpass networks in a parallel-cascade configuration

A new approach to designing absorptive microwave filters using allpass networks in a parallel-cascade configuration is presented. A signal is divided into two paths, each comprised of a number of cascaded allpass networks. The two signals are then recombined, and frequency selectivity results from phase cancellation. It is shown that this approach is especially useful for dissipative loss compensation. A general method for designing the microwave allpass networks is given. Bandpass and bandstop microstrip prototypes were designed, built, and tested.