Synthesis Design of Filtering Differential Phase Shifters of Independently Suppressed Harmonics

This brief proposes a class of filtering differential phase shifters with independent phase shift response and effective harmonic suppression. Different from the traditional single-mode resonator topology, dual-mode resonators are utilized here for single-band phase shifters. By adjusting its impedance values, the harmonics can be aligned without affecting its in-band filtering and phase shift characteristics. Furthermore, scaled line transformation are furtherly introduced for extended stopband bandwidth. By combining the dual-mode resonator with its scaled lines, the proposed phase shifters can readily realize desired phase shift response and independently suppressed harmonics. A generalized circuit model is established for closed-form synthesis design of the presented phase shifters with any arbitrary odd order. In the end, the 3^{\mathrm{ rd}} - and 5^{\mathrm{ th}} -order filtering differential phase shifters are designed and fabricated for verification. It is found that the simulated and measured results are in good agreement.