Bandwidth Optimization Method for Reflective-Type Phase Shifters

This paper discusses a novel optimization technique for broadband reflective-type phase shifters (RTPS). The performance characteristics of an RTPS, including its achievable maximum phase shift and the corresponding average loss, are calculated on the basis of simulated or measured varactor data. In addition, the root-mean-square (rms) errors are evaluated to determine the broadband performance of the device. To extract the characteristics, a reciprocal, lossless matching network with arbitrary output impedance is connected in series to the varactor. The results are plotted on Smith charts, which yield an intuitive representation of the matching network area to achieve the design goals. The technique is verified by realizing a WR-3 band (220-325 GHz) RTPS microwave monolithic integrated circuit realized in a 50-nm metamorphic high electron mobility transistor InGaAs technology. The measured phase shift is 118° at the center frequency of 240 GHz with a bandwidth of 62 GHz. The rms phase and amplitude errors are lower than 5.6° and 0.67 dB, respectively.