Wideband Tunable Differential Phase Shifter With Minimized In-Band Phase Deviation Error

This letter presents a tunable differential phase shifter with wideband flat phase characteristics. The proposed structure consists of a power dividing circuit and two 3-dB hybrids. To achieve the tunable flat phase characteristics over a wide bandwidth (BW), the coupled and through ports of one hybrid is terminated with short-circuited transmission lines (TLs), whereas those of another hybrid are terminated with a TL and varactor diode. For experimental validation, the proposed structure was designed and fabricated at a center frequency of 2.5 GHz. From the measurement results, the fabricated circuit provided a tunable differential phase shift range of 89° to 193° with a maximum in-band phase error of ±8.6° over a BW of 1 GHz.