WIDEBAND AND UWB COMMON‐MODE SUPPRESSED DIFFERENTIAL‐MODE FILTERS BASED ON COUPLED LINE SECTIONS

This chapter introduces different kinds of coupled lines to design balanced filters with ultra‐wideband (UWB) or wideband differential‐mode bandpass responses and high common‐mode suppression. It discusses the novel filters that include UWB balanced filters combining UWB bandpass filter (BPF) and UWB bandstop filter(BSF), wideband balanced filters using coupled line stubs, wideband balanced filters with internal cross‐couplings, wideband balanced filters using stub‐loaded ring resonators (SLRRs), and wideband balanced filters using modified coupled feed lines (MCFLs) and coupled line stubs (CLSs). Balanced filter can be realized by combining the traditional BPF and BSF. To achieve high selectivity in differential mode and enhanced rejection in common mode, more transmission zeros should be introduced. Another simple and innovative approach is proposed to design balanced wideband filter with high selectivity and common‐mode suppression. The chapter shows the circuit model and layout of the proposed balanced BPF, which contains two SLRRs.