A widely tunable filter configuration composed of high Q RF resonators and variable capacitors

This paper proposes a filter configuration with wide tunability, which is composed of high Q RF resonators and variable capacitors (VCs). High Q resonators can be realized by surface and bulk acoustic wave (SAW/BAW) technologies. At first, the fundamental operation of the filter is presented, and it is shown how the center frequency and the passband width are adjustable with the VC setting. It is also shown that narrow transition bands are realizable when multiple stages are cascaded with mirror inversion. Then, influence of Q factors is discussed. Finally, two types of tunable filters are designed, and applicability of this filter topology is demonstrated. Furthermore, the filter configuration is realized using SAW resonators and fixed capacitors, and its operation is simulated.