Design technique for varactor analog phase shifters with equalized losses

Abstract

The paper presents a novel design technique for reflection-type varactor analog phase shifters based on tunable reflective loads. The reflective load comprises two similar tuning stubs with incorporated varactor diodes, where each varactor can be tuned independently. It is shown that by an appropriate losses equalization method applied together with a specific independent varactors control algorithm it is possible to achieve the desired 360° phase shift with stabilized losses, which are significantly lower compared to the well-known single-channel design. We derive and discuss in details main design relations arisen from the complex plane reflection coefficient consideration. The presented technique is first verified by circuit simulation in ADS, and comparison with the classical single-channel design is also considered. Next, we develop experimental prototypes of a reflective load and a full phase shifter based on a packaged silicon varactor diode for operation in C-band with 5.8 GHz central frequency. Experimental and theoretical results are in perfect agreement. Moreover, we have found that the bandwidth of the proposed phase shifter can be greatly enhanced if the reflective loads are tuned at each sub-band using a unique optimal tuning path. The suggested reflective load demonstrates the total bandwidth of 10.3% and the instantaneous bandwidth of 1.7% (sub-band), where inside each sub-band measured ripple at the central frequency is around 0.5 dB, and the maximum overall ripple is below 0.8 dB.