A 14.7 GHz Lithium Niobate Acoustic Filter with Fractional Bandwidth of 2.93%

This work presents the first demonstration of a wideband hybrid monolithic acoustic filter in the K
_u
-band that overcomes the electromechanical coupling (k
_t
2) limit on the fractional bandwidth (FBW) of conventional ladder topology acoustic filters. This work employs the bandwidth-widening technique of combining a shunt inductor to a resonator to compensate for low k
_t
2. The filter combines electromagnetic and acoustic structures to take the advantages of both: wideband, high Q, and compact sizes. The fabricated filter based on the fifth-order antisymmetric Lamb wave mode (A5) with 1.1% k
_t
2has a 3-dB FBW of 2.93% at 14.7 GHz, stopband insertion loss of 19.5 dB, with a small footprint of 2.25 mm
²
.