Microwave Communication Filters

This paper considers the various design procedures for microwave bandpass channel filters which are of sufficiently narrow fractional bandwidth such that they may be designed directly from low-pass prototypes. Initially, the more conventional forms are considered e.g., (Thompson, Butterworth, Chebychev, Elliptic Function etc.) and typical physical realizations are presented. However, for high capacity systems with narrow guard bands between channels, it is essential to turn to non-minimum phase structures to minimise distortion. Historically, the inclusion of all-pass delay equalizers in addition to the conventional minimum phase filters were the first practical non-minimum phase microwave devices. Recently, however, superior design procedures have become available with compact physical realizations in the microwave regions. These structures are considered in detail including very recent design work relating to the optimum design of channel filters for arbitrary modulated carriers. Experimental results verify that theoretical specifications may be met in practice with only a small increase in size and cost over unequalized conventional filters.