Additively Manufactured Dual-Mode Reconfigurable Filter Employing VO₂-Based Switches

Modern wireless devices operate on multiple frequency bands and, thus, can benefit from frequency-reconfigurable radio frequency (RF) components, especially filters that are typically larger in size and are required for every frequency band. In addition, many applications, such as wearable electronics, desire stable performance from the devices when they are bent or flexed. However, most of the reconfigurable filters are built on rigid substrates and utilize expensive discrete RF switches, which needs to be soldered to the filters. In this work, we present a fully printed filter that achieves reconfigurability through printed vanadium dioxide (VO2)-based switches that are extremely low cost and do not require any soldering for their attachment. The filter design is based on a dual-mode resonator, which enables a second-order filter despite a single resonator, thus helping in making the filter compact. It also helps in maintaining a decent insertion loss (2.6 dB), despite relatively low conductivity of the metallic ink. The switches, when activated thermally through a printed heater at the backside, reconfigure the frequency from 4 to 3.75 GHz. The filter has been realized on a flexible Kapton substrate, making the filter conformable to any surface. Measurements under various bending conditions reveal stable performance, making this filter design suitable for a number of wearable and the Internet-of-Things applications.