Dual-Band and Reflectionless Wideband Filtering Phase Shifters Based on Asymmetric Broadside-Coupled SCPW-MS With Discrete Air Cavities

Two novel filtering phase shifters (FPSs) based on broadside-coupled suspended coplanar waveguide and microstrip (SCPW-MS) hybrid structures with discrete air cavities are proposed in this article. First, a new dual-band FPS (DBFPS) is constructed using five asymmetric broadside coupled lines (ABCLs), where the first two ABCLs are designed as bandstop sections and the subsequent two are implemented as wideband bandpass sections. Significantly, the final coupled line (CL) in the bandpass section is utilized as a phase-shifting unit to achieve integrated filtering-phase-shifting functionality. A parallel short-ended ABCL is incorporated to introduce transmission zeros (TZs) at both passband edges for enhancing selectivity. Then, a new reflectionless wideband FPS (RWFPS) is developed based on a complementary diplexer topology, where a three-ABCL wideband bandpass filter (BPF) is combined with compact resistively terminated bandstop branches for effective out-of-band reflection absorption, featuring exceptionally flat in-band response and broadband reflectionless characteristics. Experimental verification demonstrates that the DBFPS works at 3.9 and 6.15 GHz with insertion losses of 0.29 and 0.65 dB, 3-dB fractional bandwidths (FBWs) of 32% and 21%, and phase errors below ±4° and ±5° for the 90°/90° phase shifts, respectively. Additionally, the RWFPS demonstrates a center frequency of 5.65GHz with an insertion loss of 0.33 dB, and a 3-dB FBW of 90% and maintains a $90^{\circ }~\pm ~6.8^{\circ }$ phase shift across 3.38–8.18GHz while exhibiting a return loss better than 10 dB from dc −12GHz.