Tunable Filter Based on Hybrid Microstrip and 35% Electroacoustic Coupling SH ₀ -Wave Resonators

This article presents the full development of a tunable filter based on electroacoustic resonators. The overall structure consists of a hybrid topology combining microstrip sections to interconnect the tunable components (varactors), the DC-feeding blocks, and the on-chip fabricated electroacoustic resonators. The in-house developed resonators exhibit a very high electroacoustic coupling (35%), enabling an in-line filter topology in which the acoustic resonators are coupled through variable capacitors (varactors). The filter is centered at 1 GHz with a 10-MHz bandwidth and comprises four resonators and 11 varactors, allowing independent control of the resonators’ resonant frequencies, the inter-resonator coupling, and the input/output matching. The whole filter fits within a reduced area of 7×16 mm2, including the DC-feeding blocks with the corresponding lumped inductances and capacitances. The filter has been manufactured and measured, demonstrating a feasible tuning range of 40 MHz and a bandwidth control of 100%.