Design of 2-Track DMS SAW Filter with Low Loss, High Selectivity and Compact Size for Band-29 Applications

In this paper, a miniaturized surface acoustic wave (SAW) bandpass filter for Band-29 applications is designed, fabricated, and measured. The proposed filter is composed of two symmetrically cascaded double-mode SAW (DMS) structures with the same configuration. Each DMS comprises five interdigital transducers (IDT) with pitch modulation. The operating mechanism of the 2-track DMS filter is elucidated through even- and odd-mode analysis methodologies, and the lumped-element equivalent circuit of the proposed filter is derived. Flexible control over even- and odd-mode resonances, along with the positioning of the transmission zero (TZ) at the left side of the passband, is achieved by adjusting the pitch sizes of different IDT groups. Various grounding strategies are explored to enhance the out-of-band rejections. The proposed filter is simulated by both the coupling-of-modes (COM) model and the finite element method/boundary element method (FEM-BEM). For verification, the filter is fabricated, and packaged, demonstrating good agreement with the simulated performance.