Constructing a Microstrip Phase Shifter with Low Phase Error Using a Y-Resonator

In this paper, we propose a Y-type dual-mode microstrip phase shifter that utilizes input–output cross-coupling. The structure comprises a main line and a reference line, with the main line designed in a cross-coupled parallel-feeding configuration to create a band-pass filter. The single-mode resonance frequency is fine-tuned to meet the bandwidth requirements of the band-pass filter. Additionally, by introducing new symmetric transmission zeros in the upper and lower cutoff bands through the cross-coupling of the input and output feed lines, we achieve a quasi-elliptic response. This design significantly enhances both the passband and out-of-band performance of the filter. The reference line functions as a uniform transmission line, and the phase shift value of the phase shifter is achieved by adjusting its electrical length. Compared to conventional phase shifters, this design offers several advantages, including a simpler structure, reduced phase error, and a wider phase shift range. Ultimately, a 90° to 225° phase shifter was designed and simulated, while a 90° phase shifter was fabricated and tested. Measurement results indicate that the designed phase shifter successfully achieves a phase shift of 90° ± 1.2°, with S11 less than 16.5 dB and a fractional bandwidth (FBW) of 60.8%.