Upper 6 GHz Acoustic Delay Lines With Suppressed Group Delay Dispersion and Low Propagation Loss on LiNbO 3 /SiC Substrates

This work presents upper 6 GHz (U6G) acoustic delay lines (ADLs) on lithium niobate/silicon carbide (LNSiC) heterogeneous substrates with flat group delay, high phase linearity, and low propagation loss (PL). Based on LNSiC substrates, the high-velocity longitudinal leaky surface acoustic wave (LL-SAW) mode is effectively excited and well confined. The effect of in-plane orientations ($\theta $) on group-delay flatness and phase linearity of ADLs is explored, which is not systematically investigated for strongly in-plane anisotropic heterogeneous substrates such as LNSiC. Contrary to the prevailing designs prioritizing high-$K^{2}$configurations (e.g.,$\theta $= 36°) to achieve low insertion loss (IL) and large fractional bandwidth (FBW), a new ADL design strategy focusing on group delay dispersion suppression is proposed while maintaining comparable FBW. The fabricated LL-SAW ADLs exhibit a center frequency of 6.74GHz, a minimum IL of 9.73 dB with group delay of 50 ns, a 3-dB FBW of 7.66%, and an extremely low PL of$5.03\times 10^{-3}$dB per wavelength (dB/$\lambda $). The angular sweep of$\theta $validates that the propagation direction of 90° significantly reduces the group delay fluctuation from 46.2% to 13% and the residual sum of squares (RSSs) from 1487.7 to 17.2 rad2at 100-ns group delay. The experiment results confirm the effectiveness of angle-dependent design in improving group delay stability. These findings provide a new design perspective to develop ADLs with flat group delay, high phase linearity, and low PL for RF analog signal processing in 5G/Wi-Fi 7 systems.