Acoustic wave filter with reduced bulk-wave scattering loss, ladder filter incorporating same and method

An acoustic wave filter with reduced bulk-wave scattering loss, said acoustic wave filter having a center frequency and an acoustic wavelength associated with said center frequency, said acoustic wave filter comprising:

• an acoustic wave propagating substrate;
• a first reflector comprising a first group of reflective elements each having a first breadth, said first group of reflective elements periodically disposed along a preferred axis on a first surface of said acoustic wave propagating substrate and having a first period;
• a first transducer disposed to a first side of said first reflector, said first transducer comprising a first group of electrodes each having a second breadth, said first group of electrodes periodically disposed along said preferred axis on said first surface and having a second period, said first transducer for providing acoustic waves traveling in either direction along said preferred axis in response to electrical stimulation, thereby insonifying an acoustic path via propagation of said acoustic waves, and for providing electrical signals in response to acoustic waves incident on said first transducer;
• a first gap having a first width, said first width exceeding one-fourth of said acoustic wavelength, said first gap disposed between said first reflector and said first transducer on said first surface;
• a second reflector comprising a second group of reflective elements each having said first breadth and periodically disposed along said preferred axis on said first surface, said second reflector disposed to a side of said first transducer opposite said first reflector;
• a second gap disposed on said first surface between said first transducer and said second reflector, said second gap having a second width;
• and
• a first plurality of waveguiding elements aperiodically disposed within said first gap.

An acoustic wave filter with reduced bulk-wave scattering loss, said acoustic wave filter having a center frequency and an acoustic wavelength associated with said center frequency, said acoustic wave filter comprising:

• an acoustic wave propagating substrate;
• a first reflector comprising a first group of reflective elements each having a first breadth, said first group of reflective elements periodically disposed along a preferred axis on a first surface of said acoustic wave propagating substrate and having a first period;
• a first transducer disposed to a first side of said first reflector, said first transducer comprising a first group of electrodes each having a second breadth, said first group of electrodes periodically disposed along said preferred axis on said first surface and having a second period, said first transducer for providing acoustic waves traveling in either direction along said preferred axis in response to electrical stimulation, thereby insonifying an acoustic path via propagation of said acoustic waves, and for providing electrical signals in response to acoustic waves incident on said first transducer;
• a first gap having a first width, said first width exceeding one-fourth of said acoustic wavelength, said first gap disposed between said first reflector and said first transducer on said first surface;
• a second reflector comprising a second group of reflective elements each having said first breadth and periodically disposed along said preferred axis on said first surface, said second reflector disposed to a side of said first transducer opposite said first reflector;
• a second gap disposed on said first surface between said first transducer and said second reflector, said second gap having a second width;
• a first plurality of waveguiding elements aperiodically disposed within said first gap including a first waveguiding element adjacent said first reflector, said first waveguiding element having a third breadth equal to said first breadth plus:
• a first amount equal to a difference between said first and second breadths, divided by a number of waveguiding elements included in said first plurality of waveguiding elements;
• a second transducer disposed between said first transducer and said second reflector such that said second gap is disposed between said second transducer and said second reflector;
• and
• a second plurality of waveguiding elements aperiodically disposed in said second gap.