Electronically Tunable Reflection Type Phase Shifters

This brief presents a low loss reflection-type phase shifter (RTPS) using a single varactor diode as the load. A parallel combination of an open-circuited stub and a varactor loaded stub are used at the load terminal. This arrangement greatly improves the response of the phase shifter. A transmission line based analysis shows real part of the load plays an important role on both phase variation and insertion loss. Based on the analysis, design guidelines are provided for controlling maximum insertion loss of the phase shifter. A prototype phase shifter is fabricated at 10 GHz. Measurement results of the RTPS show a relative phase variation of 190° with a maximum insertion loss of 2 dB when varactor capacitance is varied over 0.1 pF-0.2 pF. Moreover, the return loss is always better than 20 dB over the entire tuning range of the RTPS.