WIDEBAND BALANCED FILTERS BASED ON MULTI‐SECTION MIRRORED STEPPED IMPEDANCE RESONATORS (SIRs)

This chapter aims to study some implementations of wideband balanced bandpass filters based on multi‐section mirrored stepped impedance resonators (SIRs) and to provide guidelines for their design. Through the use of such resonant elements, it is possible to achieve wideband differential‐mode responses and an efficient common‐mode rejection by the selective introduction of transmission zeros for the common mode. The chapter also reports three filter examples, including an order‐5 and an order‐7 wideband filter, both based on 7‐section SIRs coupled through admittance inverters, and an order‐5 ultra‐wideband (UWB) balanced filter based on 5‐section SIRs and patch capacitors. In order to implement the balanced filters, the mirrored SIRs are alternated either with balanced quarter‐wavelength transmission‐line sections (acting as admittance inverters) or with series resonators (in balanced configuration) implemented by means of lumped elements (interdigital or patch capacitances and inductive strips).