Balanced Filtering Phase Shifters With Low Phase Deviation and High Common-Mode Suppression

Abstract

In this paper, a type of balanced filtering phase shifters (BFPSs) with low phase deviation, high common-mode (CM) suppression, and steep filtering property, is proposed. The proposed phase shifter consists of the folded asymmetric step impedance resonator (FASIR) and the folded symmetric step impedance resonator (FSSIR). Owing to two additional coupling paths, two transmission zeros (TZs) are generated, which improves the selectivity of the differential-mode (DM) passband. By employing the stepped impedance slotlines and U-shaped microstrip lines (SU) transition structures, the 40 dB CM suppression fractional bandwidth (FBW) of 350% is achieved. The synthesis method to design the proposed BPFS with the specified DM phase shift value, phase deviation, and bandwidth is presented. And the 15°, 30°, 45°, 60°, 75°, and 90° balanced filtering phase shifters are designed and exhibited. For the reference line and the six main lines, the filtering passbands and phase shift bands are in relative agreement. To verify the design principle, two archetypes are manufactured and measured, which exhibit that the phase deviation for 45° (90°) is only 1.5° (2.4°).