Transformers with incorporated filtering capabilities exploiting signal-interference principles

Double-functionality microwave planar circuits hybridizing filtering and impedance transformation capabilities are reported in this work. They are based on signal-interference transversal filtering sections (TFSs) whose design equations are generalized to synthesize the filtering functionality between any pair of real port impedances. Thus, an inherent impedance-transformation action is added to the signal-interference filter in its passband(s). The devised dual-functionality circuit concept is valid for other types of TFSs, as well as for both single- and multi-band designs. For experimental verification, two double-function microstrip prototypes for dual-band and ultra-wideband single-band filtering specifications which feature transformation ratios of 2:1 are synthesized, constructed, and characterized.