I. Introduction
A conventional RF frontend module consists of many filters where each filter is allocated for a specific frequency band. These filters are connected through multiplexing switch networks to support multi-band wireless standards. Using an individual filter for each band increases the module size, power consumption and cost. Therefore, implementation of reconfigurable filters that can operate at different frequency bands while maintaining key RF performance characteristics such as low insertion loss, good linearity and power handling is necessary for manufacturing of future RF frontends. For implementation of a reconfigurable filter, there is a need for reconfigurable resonators that can be tuned and operate at different frequency bands. Reconfigurable resonators and filters using MEMS technology and active tuning elements have been presented in literature [1], however most of the existing tunable solutions are based on planar transmission-line or nonplanar cavity structures that are too bulky. Surface Acoustic Wave (SAW) technology is traditionally used in many consumer wireless filtering applications due to the ease of manufacturing, lower cost, and good RF performance. Recent studies have been conducted to explore the possibility of tunable RF acoustic wave resonators and filters [2]. A tunable SAW filter was presented in [3] where tuning is achieved by integrating MEMS varactors with the SAW resonator. The complex structure and manufacturing of the MEMS devices does not allow a cost-effective and compact implementation while maintaining an acceptable RF performance. Another reconfigurable piezoelectric resonator was presented in [4] by utilizing phase change material programmable vias between the electrode connections. The resonator in [4] achieves different impedance states but it does not have frequency tuning capability and the performance characteristics are not sufficient for practical implementation of a filter. This paper presents a method for construction of a reconfigurable SAW resonator where the tuning element is monolithically integrated with the resonator. A non-traditional SAW resonator configuration is proposed where tuning of the resonance frequency is achieved by creating low and high impedance paths between certain tuning electrodes and the interdigitated electrodes of a SAW resonator. Vanadium Dioxide (VO2) elements are used as switching elements that can be easily integrated within the proposed structure of the resonator.