Proposal and Synthesis Design of Wideband Filtering Differential Phase Shifters With a Pair of Out-of-Band Transmission Zeroes

In this paper, a new class of wideband filtering phase shifters with a pair of controllable out-of-band transmission zeroes is presented for the first time. The proposed wideband filtering differential phase shifter consists of two stub-loaded multimode resonators (SLMMR) in the main and reference branches, which can provide a constant phase shift and self-realized generalized Chebyshev filtering function with controllable transmission zeroes by properly setting the impedance ratio R
_z
of the loaded stub. On the one hand, the prescribed phase shift value, phase deviation, and phase shift bandwidth are deduced that basically dominated by resonant modes of SLMMR together with electrical lengths of the phase-shifting lines. On the other hand, the phase properties of transmission zeroes are systematically investigated to demonstrate that they arouse little effect on the phase shift performance, but highly improve the frequency selectivity in theoretical analysis. Based on the presented synthesis method which simultaneously considers wideband phase shift and bandpass filtering function, the circuit parameters of the entire proposed phase shifter can be synthesized with prescribed phase shift value, phase deviation, bandwidth, return loss, and transmission zero positions. Besides, the phase shift and return loss bandwidth can be determined in the design process. As design examples, two 90° wideband filtering phase shifters with different specifications are synthesized, designed, and fabricated to validate our proposed approach.