A Balanced Phase Shifter With Common-Mode Suppression

In this paper, a balanced phase shifter using coupled line with loaded transmission line is proposed, which is the first balanced passive phase shifter providing both differential-mode (DM) phase shift and common-mode (CM) suppression simultaneously. Furthermore, the proposed design can provide (30 degrees-90 degrees) phase-shift range with characteristic of the wide bandwidth. Compared with single-ended phase shifters, the proposed design can be directly utilized in differential system without additional baluns. Compared with the state-of-arts balanced passive phase shifters, the proposed one shows the advantages of the CM suppression, wider bandwidth, wider alternative phase-shift range, and simpler structure. Three DM transmission poles can be obtained to support the wide bandwidth. Complete theoretical analysis and discussion are given to guide the design. To verify the theoretic prediction, three prototypes are designed with the operation bandwidth for 30 degrees +/- 2.5 degrees (60 degrees +/- 4.2 degrees and 90 degrees +/- 5.5 degrees) of 68% (70% and 73%), with the minimum insertion of 0.2 dB (0.15 dB and 0.27 dB), with the CM suppression better than 10 dB, and with the minimum return loss of 17.8 dB (18.5 dB and 15.1 dB), respectively.