A Sub-THz Rectangular Waveguide Phase Shifter Using Piezoelectric-Based Tunable Artificial Magnetic Conductor

An analog phase shifter operating at 240 GHz and implemented within a rectangular waveguide is presented in this paper. The phase shifter relies on mechanically actuating a tunable perfect magnetic conductor (PMC) inside an upright rectangular waveguide supporting a modified TE₁₀ mode. The PMC boundary condition is realized using a metallic strip suspended slightly above the short wall of the rectangular waveguide. It is shown analytically and numerically that vertically actuating the metallic strip changes the dispersion relation of the modified TE₁₀ mode leading to a controllable phase shift. The proposed structure is designed using full-wave simulations and optimized for minimal losses. It is then fabricated using standard silicon microfabrication techniques including photolithography, deep reactive ion etching, and metal sputtering. The actuation is done through an external piezoelectric actuator that is assembled with the microfabricated structure to form a single unit. The phase shifter shows a measured phase shift of 380° with worst case insertion loss of 3 dB leading to an excellent figure of merit (FoM) of 127°/dB. To the best of our knowledge, this is the best reported FoM for all passive phase shifters operating beyond 60 GHz.