P2N-1 Suppression of Spurious Responses for Ultra-Wideband and Low-Loss SAW Ladder Filter on a Cu-grating/15°YX-LiNbO3 Structure

This paper describes the development of extremely wideband and very low-loss RF SAW filters of ladder type for future communication systems. Because of its large electromechanical coupling factor for SH-type SAWs, a Cu-grating/15degYX-LiNbO₃ structure was employed as a substrate. At first, four-stage ladder type filter was designed and fabricated, where width/length weighted dummy electrodes were used to suppress spurious responses caused by transverse-mode resonances. In addition, a viscous film was coated on the filter surface which is effective in suppress a spurious dip caused by Rayleigh SAWs. As the result, the fractional -3dB bandwidth of 19% and minimum insertion loss of about 0.6 dB were simultaneously achieved around 1 GHz, which basically owes the high electromechanical coupling and high Q factor of SH type SAWs propagating in the structure