Thermally Controlled Coplanar Microwave Switches

Novel coplanar microwave switches have been designed, fabricated, and tested. The switching element consists only of a thin vanadium dioxide (VO2) film patch. VO2 exhibits a first-order phase transition from a semi-conducting low temperature phase to a metallic high temperature phase resulting in an abrupt change of the electrical resistivity from 3·100 ¿cm to 3·10¿4 ¿cm at a phase transition temperature of Tt = 64°C. The switches have been designed for 24 GHz operation. In the "on"-state above Tt an insertion loss of 2.7 dB has been measured for a single pole single throw (SPST). At 60°C the switch is "off" resulting in an isolation of ¿25 dB. The dynamic range of the switch is higher than 22 dB. Additionally an SPDT (single pole double throw) has been realized, fabricated, and tested. The insertion loss is about 2 dB, the switching isolation is better than 18 dB.