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The letter deals with the effects of diffraction or beam spreading on frequency response of bulkacoustic-wave-beam filters. Theoretical analysis for 41Â°-rotated Y-cut LiNbO3 has shown that, when the propagation distance is comparable to the acoustic length of the interdigital transducers (IDTs), the bandwidth is significantly increased over the SAW response with the same IDTs. If the propagation distance is within several times the IDT acoustic length, insertion loss is almost independent of propagation distance. These results suggest that there may be a situation where an increased fractional bandwidth for a given insertion loss is achievable. An experimental result was compared with the theoretical calculation.