Design of a Compact SISL BPF With SEMCP for 5G Sub-6 GHz Bands

In this letter, a cross-coupled dual-bandpass filter (BPF) with separate electric and magnetic coupling paths (SEMCPs) for 5G sub-6 GHz applications is proposed. Source-to-load couplings are also introduced in this structure for the flexibility of heterogeneous feed lines. Five controllable transmission zeros (TZs) in total are produced in the dual-band filter. The filter achieves good overall performance by adopting two pairs of quarter-wavelength stepped-impedance resonators (SIRs). To minimize the size of the filter and enlarge the controllable range of the second passband, the SIRs forming the second passband are separated and folded onto two different layers. The measured dual band filter achieves fractional bandwidths of 7.82% and 4.08%, centered at frequencies of 3.45 and 4.9 GHz with insertion losses of 1.15 and 1.42 dB, respectively.