A Low-Loss Lithium Niobate on Sapphire SH-SAW Delay Line with Rayleigh Mode Mitigation via Multistrip Couplers

In this work, we demonstrate, for the first time, a low-loss shear-horizontal surface acoustic wave (SH-SAW) delay line utilizing multistrip couplers (MSC)-based track exchanger, implemented on lithium niobate-on-sapphire platform. Due to the significant difference in electromechanical coupling factor between the Rayleigh and SH-SAW modes, the number of MSC strips optimized for the SH mode is insufficient to enable energy transfer of the Rayleigh mode between tracks, thereby achieving efficient mode separation. The fabricated MSC-equipped SH-SAW delay line achieves approximately 25 dB suppression of the adjacent Rayleigh band compared to the reference design, along with a low insertion loss (IL) of 4.94 dB, a wide fractional bandwidth (FBW) of 5.21%, and a medium delay time of 68.75 ns, enabled by the thin-film acoustic waveguide structure. These high-performance characteristics underscore the strong potential of this approach in expanding the design space for RF applications.