K a-band waveguide phase shifter using tunable electromagnetic crystal sidewalls

Tunable electromagnetic crystal (EMXT) structures have been used as sidewalls in special waveguides for frequencies of 30-40 GHz. This has the effect of substituting tunable impedance surfaces in place of the normal conducting metal sidewalls. The resulting EMXT waveguide boundary conditions can then be controlled in situ to achieve desired phase shifting and/or field flattening effects. Proof-of-concept experiments have been done using fix-tuned EMXT sidewalls with various resonant frequencies, and the measurements indicate that the insertion loss is low. An InP quantum barrier varactor approach is used to implement the tunable K a-band EMXT waveguide phase shifter. The dependence of transmission amplitude and phase on the center frequency of sidewall resonance has been simulated and measured. Measurements and simulation results agree very well. The loss mechanism of the demonstrated phase shifter is well understood. Our results indicate that tunable EMXT waveguide will provide simple and low-loss phase-shifting systems.