Wideband Tunable Phase Shifter With Low In-Band Phase Deviation Using Coupled Line

This letter presents a design for a wideband reflection-type tunable phase shifter (RTPS) with a low in-band phase deviation error. The proposed RTPS consists of a 3-dB hybrid where a through port and a coupled port are terminated with coupled lines, varactor diodes, and a capacitor. The measured capacitance of the varactor diodes was used in the analysis to take into account the in-band phase deviation error caused by the parasitics of the varactor diode. The analysis shows that the desired phase shifting range (PSR) and a low in-band phase deviation error can be obtained by properly selecting the characteristic impedance and coupling coefficient of the coupled line and load capacitance. The experimental results show that the fabricated RTPS provides a PSR of 146.93° at 2.5 GHz and an in-band phase deviation error of ±5.79° within 500 MHz. Moreover, the input-output return losses are higher than 15.76 dB, and the insertion loss is smaller than 1.29 dB within the operating frequency band.