Broadband Low Phase Error Phase Shifter Using High-Pass Network With a Coupled Line Section

Abstract

This letter presents a method to realize a broadband 90 $^{\circ}$ differential phase shifter which uses a high-pass network with a coupled line section for reducing the phase error to less than 2 $^{\circ}$ . Adding the coupled line section in the high-pass network, the local maximum and the second local minimum of phase shift can be created because the proposed phase shifter operates as a high-pass network at low frequency and operates as a coupled line at high frequency. The ratio of L over C, length and impedance of the coupled line are designed, and the limitation by fabrication is also relaxed because the strong coupling for the coupled line is not required for this 90 $^{\circ}$ differential phase shifter. The experimental results show the fractional bandwidth (FBW) of 125% with low phase error of $\pm 2^{\circ}$ and the return loss is better than 11 dB from 1.7 to 7.4 GHz.