Surface elastic wave filter with resonant cavities

A surface elastic wave filter with resonant cavities, comprising:

• a composite substrate formed of a base substrate and a piezoelectric upper layer;
• at least one input electroacoustic transducer and at least one output electroacoustic transducer, disposed on the piezoelectric upper layer;
• at least one internal reflective structure, arranged between the at least one input electroacoustic transducer and the at least one output electroacoustic transducer, the at least one internal reflective structure comprising:
• a first structure comprising at least one reflection grating having a first period;
• a second structure comprising at least one reflection grating having a second period, the first period being greater than the second period;
• wherein the at least one reflection grating of the first structure comprises a first plurality of reflection gratings separated from each other by a first distance, the at least one reflection grating of the second structure comprises a second plurality of reflection gratings separated from each other by a second distance, and wherein a distance separating the first structure and the second structure is equal to an arithmetic mean, to within 10%, of the first distance and the second distance.