Compact Filtering Phase Shifter With Simple Structure

A compact filtering phase shifter is proposed using two quarter-wavelength coupled lines, two quarter-wavelength transmission lines, and two face-to-face feed lines. With such a circuit model, the proposed design has the advantage of compact size and simple structure compared with the state-of-the-art designs. Multiple transmission zeros (TZs) can be obtained. Constant passband for different phase shifts can be achieved by controlling the parameters of coupled lines and transmission lines. Theoretical analysis based on the even-/odd-mode method guides the design. Two prototypes with the phase shifts of 45° and 90° are designed for verifying the theoretical analysis. It is shown that the 45° (90°) phase shifter can obtain 45° ± 2.3° (90° ± 4.3°) for the 3-dB bandwidth of 51% (51%), the phase shift bandwidth of 57% (58%), and the size of $0.5\lambda _{\mathrm {g}} \times 0.01\lambda _{\mathrm {g}}$ ( $0.7\lambda _{\mathrm {g}} \times 0.01\lambda _{\mathrm {g}}$ ), where $\lambda _{\mathrm {g}}$ is the guided wavelength at the center frequency.

I. Introduction

Filtering phase shifters can acquire constant phase shift and passband at the same time without increasing the number of devices, which is different from the phase shifter [1]–[10] containing just the function of phase shift. The filtering phase shifter is becoming the key point in the phase shifter field. Furthermore, compact size with a simple structure is very important for filtering phase shifters because the requirement for system integration and simplification are becoming more and more stringent.