A novel wideband multi‐mode coupled resonator filter based on bulk acoustic wave technology.

This paper proposes a novel multi‐mode bulk acoustic wave (BAW) coupled resonator filter (CRF) for wideband applications. Three stepped‐impedance coupling layers of CRF are used to generate multi‐mode properties, and external inductors are added for port match. To facilitate the calculation of resonance frequencies, a simplified Mason model is derived and applied in the even‐ and odd‐mode analysis of CRF. Based on different acoustical length of CRF coupling layers, four cases that are applicable for different filter bandwidth are proposed. From these cases, fractional bandwidth (FBW) of the multi‐mode CRF can be realized in a wide range from 12.8% to 33% when the coupling layers adopt the commonly used SiO2/Mo/SiO2 materials. Moreover, the tuning range of FBW can be further enlarged by changing the materials of coupling layers. To verify the proposed multi‐mode CRF, a triple‐mode n77 band filter with center frequency of 3.723 GHz and FBW of 24.2%, and a penta‐mode filter with a larger FBW up to 33% are designed and simulated. Simulation results of the original Mason model, the simplified Mason model, and the three‐dimensional (3D) model based on the finite element method are consistent well with each other. [ABSTRACT FROM AUTHOR]