A Low-Loss Voltage-Controlled Analog Phase-Shifter Using Branchline Coupler and Varactor Diodes

This paper proposes a new type of continuously tunable voltage-controlled analog phase shifter for radio frequency and microwave-frequency applications. The design uses a branchline coupler and two varactor diodes. The concept has been tested at 900MHz using FR4 dielectric material using thin-film microstrip technology. The measured phase shift variation is 115 degree over the entire range of the control voltage. The measured insertion loss is typically better than 1.5dB and the measured return loss is better than -15dB. The performance can be further improved by using lower-loss dielectric materials. The design is also scalable to other frequency bands.