50–110-GHz Continuous GaN MMIC Reflective Phase Shifters

This article presents design, simulation, and measurements of continuous 90° and 180° phase shifters implemented in a 40-nm gallium nitride (GaN)-on-SiC process. The architecture of a single 90° reflective phase shifter uses a Lange coupler and tunable reactive loads at the “thru” and “coupled” ports. The tunable reactance is implemented with diode-connected HEMTs. Measured results show greater than 90° phase shift across 50–110 GHz with less than 10-dB average loss over a control voltage range of −1 to +1 V and a measured 1-dB compression point of 19 dBm at 95 GHz. Cascading two such phase shifters is demonstrated with a 180° phase shifter with increased insertion loss. However, toggling each set of tunable devices independently is shown to improve insertion loss by as much as 15 dB while providing the same phase change. Simulations use foundry nonlinear device models for the depletion-mode HEMTs and agree well with measured data across the 50–110-GHz range.