A Compact Balanced Phase Shifter With Wideband Common-Mode Suppression

In this paper, a balanced phase shifter using cascaded three microstirp lines and two coupled lines is proposed. The reference line is fixed without center delay line. With such configuration, wideband differential-mode (DM) phase shift can be achieved. The coupled line and half-wavelength microstrip line provide the out-of-band and in-band common-mode (CM) suppression, respectively. Compared with the state-of-the-art balanced phase shifters, the proposed balanced phase shifter has the advantages of wideband CM suppression and compact size with simple structure and fixed reference line. Theoretic analysis, parametric study and design procedure are carried out completely. To verify the theoretic prediction, two prototypes covering the frequency of 1.8 GHz are designed with the relative operating bandwidth for 45 degrees +/- 2.1 degrees (90 degrees +/- 3.7 degrees) phase shifter of 50% (53%), with the minimum return loss better than 14.7 dB, and the relative CM suppression bandwidth better than 150%.