High-Performance Surface Acoustic Wave Filters for X -Band Applications

In this work, we aim to achieve frequency boosting of high-performance surface acoustic wave (SAW) filters to X-band. Based on the LiTaO3/SiC heterosubstrate, the spurious-free SAW resonators of ultrahigh-frequency (8–10 GHz) and low-loss filters with good temperature stability are demonstrated. The fabricated SH-SAW resonators operating in the X-band exhibit a high quality factor of 350–1270, a decent coupling coefficient of 7.4%–9.6%, and the spurious-free response over a wide frequency range. The corresponding X-band filters show a low insertion loss (IL) of 1.41–1.92 dB, a 3-dB fractional bandwidth (FBW) of 4.27%–4.96%, and an out-of-band (OoB) rejection larger than 27 dB. Particularly, the one with a center frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula>) of 9.73 GHz exhibits a relatively low IL of 1.84 dB, a 3-dB BW of 416 MHz, a flat passband, and a high OoB rejection in the frequency range of 1–11 GHz. The frequency drifts of resonators and filters and the peak power-handling of filter were also measured. The results tell the excellent temperature stability and decent peak power durability of the fabricated devices. In addition, based on the same substrate, a filter array covering the entire C-band (4–8 GHz) is also prepared, demonstrating the extremely strong frequency expansion of the heterosubstrate. These demonstrated SAW devices with excellent comprehensive performances show the great potential of LiTaO3/SiC as the platform for the future wireless communications.