Vanadium Dioxide for Reconfigurable Antennas and Microwave Devices: Enabling RF Reconfigurability Through Smart Materials

We present a comprehensive study of a new method to reconfigure, tune, and/or program antennas and radio-frequency (RF) devices. The method consists of using electrical signals to induce the solid-tosolid phase transition in vanadium dioxide (VO ₂ ) thin-film patterned structures that connect the device metallization layer with extensions, thus effectively changing the geometry of the device. Applied voltage pulses to a resistive heater electrically isolated from the antenna metallization layers increase the temperature of the VO ₂ strip across the phase transition. Hence, the VO ₂ -biasing mechanism and the antenna are electrically decoupled, which enables an additional degree of freedom for antenna and microwave device engineers as the reconfiguration is no longer restricted by any biasing network limitations. Radiation patterns are also maintained unaffected. This decoupling adds into the design spectrum, applications that require wideband tuning, low-loss structures (e.g., arrays and reflectarrays), and even reconfigurable cloaks. The VO ₂ switch is arguably the smallest ever used to reconfigure an antenna, which requires further circuit element considerations. The presented method is validated through a series of antenna prototypes that demonstrate VO ₂ applicability on wire and aperture antennas. Details and challenges of the monolithic integration of VO ₂ thin films and resistive heaters for reconfigurable antennas, along with the measurement setup, are presented. Results unveil this new reconfiguration technique and suggest further applications, as the VO ₂ may also be activated optically.