New Microstrip Cascaded-Quadruplet Bandpass Filter Based on Connected Couplings and Short-Ended Parallel-Coupled Line

A cascaded-quadruplet (CQ) bandpass filter (BPF) using quarter-wave resonators is proposed based on connected couplings and short-ended parallel-coupled line (SE-PCL). The two distinct coupling mechanisms are well-characterized and employed to implement the main couplings and out-of-phase cross coupling among the CQ filter topology. Analytic design formulas with great simplicity are developed. Specifically, a microstrip CQ filter centering at 1.5 GHz with a fractional bandwidth of 10% is designed and implemented for demonstration. The measured results coincide well with the simulated ones thus validate the feasibility of the design approach.