Design of X-Band GaN Phase Shifters

This paper presents two different types of high-power gallium-nitride (GaN) phase shifters designed for X-band (8-12 GHz), but offering good performance over a much wider band. The first is a 22.5^° switched-filter phase shifter, which has much wider bandwidth than is typically found with this configuration, while maintaining low insertion loss (<; 2 dB), good return loss ( >11.15 dB), and an amplitude imbalance of less than 1.03 dB across X-band. The 1-dB compression point was higher than laboratory equipment was able to measure ( >38 dBm) and the phase shifter monolithic microwave integrated circuit exhibited an input-referred third-order intercept point (IIP₃) of 46.2 dBm. The second phase shifter is a novel design, which promises wide bandwidth (in our case, limited by the single-pole double-throw switch we have also designed), but which achieves decent insertion loss (5 dB), good return loss (better than 11 dB), and very low phase variation (1^°) across X-band, also with 22.5^° phase shift. It offers a 1-dB compression point of 30.1 dBm and an IIP3 of 46.3 dBm. The components for a 45 ^° differential phase shift using the same structure were also fabricated and verified with measurements. The high-power phase shifters have been fabricated in a 0.5- μm GaN HEMT process and were designed using an accurate customized switch field-effect transistor model.