Wideband 180° Phase Shifter Using Parallel-Coupled Three-Line

In this letter, a wideband 180° phase shifter using a parallel-coupled three-line is demonstrated. The proposed phase shifter consists of a shorted coupled line and transmission line with shorted stubs. The bandwidth of the phase shifter is increased by a high coupling factor of the coupled line. When considering a coupling factor of 1, the bandwidth is infinite and the phase error is zero. Therefore, we adopted a parallel-coupled three-line to ensure a high coupling factor. Given a limited coupling factor, the transmission line impedance is optimized for the widest bandwidth of the return loss. The designed 180° phase shifter exhibits a return loss of less than -15 dB and a maximum phase error of less than 5° in the 1.14-2.79-GHz range and its fractional bandwidth is 83.9%.