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Low-loss monolithic tunable electromagnetic crystal surfaces with planar GaAs Schottky diodes

Monolithic tunable electromagnetic crystal (EMXT) surfaces based on semiconductor varactors have been designed and fabricated for various microwave and millimeter wave applications. In order to tackle the problem of high losses associated with this kind of tunable EMXT structures, a high-quality, planar air-bridged GaAs Schottky (PAS) diode process has been developed and incorporated to produce low-loss monolithic tunable EMXT surfaces. Finite-element modeling indicates that an analog waveguide phase shifter with EMXT sidewalls can achieve 360/spl deg/ phase shift with less than 3 dB insertion loss. A backside-biasing scheme utilizing through-substrate vias has also been developed. Preliminary EMXT reflection measurements show lower loss compared with previously demonstrated tunable EMXTs. Because of the high cut-off frequency (above THz) of the GaAs Schottky diode, this EMXT technology may be readily extended to higher frequencies applications such as W-band ESA.