A Differential 90° Phase Shifter with Controllable Common-Mode Suppression

This paper presents a differential 90° phase shifter, which is constructed by coupled line and loaded transmission line with an open stub. It is not only can provide differential-mode (DM) phase shift, but also has controllable common-mode (CM) suppression. A prototype of 90° differential phase shifter is designed, the simulated and measured results have good agreement with the operation bandwidth for $\pmb{90^{\circ}\pm 5.5^{\circ}}$ of 73%, with the minimum insertion of 0.27 dB, with the CM suppression better than 10 dB, and with the minimum return loss of 15.1 dB, respectively.