Ultra-wideband longitudinally coupled-resonator filters on lithium niobate using periodically slotted SiO₂ as an acoustic coupler

Abstract

This paper discusses applicability of periodically slotted SiO2 as the coupler for ultra-wideband longitudinally coupled resonator filters (LCRFs). It is shown that -3 dB fractional bandwidth more than 31% can be achieved by using lower-order three resonance modes. It is also shown that periodically slotted SiO2 structure can also control the frequency dispersion of wave propagation along the surface, and transverse modes are suppressed well for one particular mode under a proper setting. Then the piston design is applied for remaining two modes, and the spurious-free and flat-passband triple-mode filter is synthesized.