Dynamically Reconfigurable Microwave Circuits Leveraging Abrupt Phase-Change Material

This article proposes a concept for dynamically reconfigurable distributed microwave circuits by leveraging the abrupt conductivity transition in phase-change materials (PCMs). Metallic inclusions ( $\ll \lambda $ ) are embedded in the PCM film—vanadium dioxide (VO2)—to provide low loss and reconfigurability. To validate this concept, a variety of coplanar waveguide transmission lines are designed and fabricated with metallic inclusions in VO2 films, and the lines’ performance are characterized up to 50 GHz. From measurements, a transmission-line-based model and an equivalent circuit model of the VO2 with inclusions are developed to aid in rapid design. An electromagnetic model was developed, and it indicates that loss can be close to conventional metallic distributed circuits with 100–200-nm-thick VO2 films. A criterion for maximum operating frequency is defined, and it indicates that 10- $\mu \text{m}$ unit-cells with thicker films could operate up to 60.3 GHz. Unit-cell sizes are proposed for various bands with quality factors from 10.2 to 29.3. Using the models, two applications are presented: a tunable dipole from 2.13 to 9.07 GHz and a tunable triple-stub matching network from 5 to 40 GHz with high $|\Gamma |$ . The proposed method appears viable for the realization of arbitrary programmable distributed circuits and antennas in the microwave and low-millimeter-wave bands.