Balanced Microstrip Filtering Phase Shifter Using Three-end Folded Coupled Lines

A balanced microstrip filtering phase shifter using 2 three-end folded coupled lines and 3 transmission lines is proposed. With such structure, multiple differential-mode (DM) transmission zeros (TZs) or common-mode (CM) TZs can be obtained so that good frequency selectivity or wideband CM suppression can be achieved. The phase shift covers the DM performance. Compared with the reported design, the proposed design has wider CM suppression and better frequency selectivity. One 45° prototype is demonstrated. The measured phase shift FBW(45° ± 2.3°) is 43%, 20-dB CM suppression FBW is better than 140%, and 3-dB FBW is 39.4%.