Differential Filtering Phase Shifter With Wide Common-Mode Suppression Bandwidth and High Frequency Selectivity

A differential filtering phase shifter is proposed utilizing two three-end folded coupled lines with three half-wavelength microstrip lines. Four differential-mode (DM) transmission zeros (TZs) can be obtained on both sides of the DM passband because of the cascaded two three-end folded coupled lines and one half-wavelength line. Thus, the frequency selectivity and out-of-band suppression can be enhanced. Wide CM suppression bandwidth can be obtained by the multiple common-mode (CM) TZs and the upper and lower half-wavelength lines. The phase shift bandwidth can cover the passband and the passband performance for different phase shifts can keep constant by controlling the parameters because all lines contribute to the control of phase shift deviation and 3-dB bandwidth. Compared with the reported differential filtering phase shifter, the proposed phase shifter obtains higher frequency selectivity and wider CM suppression. Complete theoretic odd- and even-mode analysis and design procedure are carried out. Two prototypes centered at 3.3 GHz are designed, which exhibit fractional bandwidth (FBW) for 45° ± 2.29° (90° ± 4°) of 42.7% (42.4%), the 3-dB FBW of 39.4% (39.4%) and the CM suppression FBW of 141% (145%).