Tunable Acoustic Filter with High-Electroacoustic Coupling Resonators

This paper presents the development of a tunable filter based on acoustic resonators with very large electroacoustic coupling. The implemented filter consists in an in-line topology where the acoustic resonators are coupled through variable capacitors (varactors). The filter is centered at$\mathbf{1 G H z}$with 10 MHz bandwidth and is formed by four resonators and eleven varactors that allow the control of individual resonant frequency of the resonators, the coupling between resonators, and the input/output matching. The whole filter has been fit in a reduced area of$7 \times 16 \mathbf{m m}^{\mathbf{2}}$, including the DC-feeding blocks with the corresponding inductances and capacitances. The filter has been manufactured and measured demonstrating a feasible tuning range of 40 MHz and a bandwidth control of$\mathbf{1 0 0} {\%}$.