Dual track SAW reflector filter using weighted reflective gratings

A dual track surface acoustic wave (SAW) reflective filter for filtering an input signal, said filter comprising:

• a piezoelectric substrate;
• a first track including a first input transducer, a first output transducer, a first reflector positioned adjacent the first input transducer and opposite to the output transducer, and a second reflector positioned adjacent to the first output transducer and opposite to the first input transducer all formed on the substrate, said first input transducer being response to the input signal and generating surface acoustic waves that propagate along the substrate, said first output transducer being responsive to the surface acoustic waves from the first input transducer and generating an electrical output signal;
• and
• a second track including a second input transducer, a second output transducer, a third reflector positioned adjacent to the second input transducer and opposite to the second output transducer and a fourth reflector positioned adjacent to the second output transducer and opposite to the second input transducer all formed on the substrate, said second input transducer being responsive to the input signal and generating surface acoustic waves that propagate along the substrate, said second output transducer being responsive to the surface acoustic waves from the second input transducer and generating an electrical output signal, wherein the reflection functions of the first reflector and the third reflector are equal in magnitude and opposite in phase and the reflection functions of the second reflector and the fourth reflector are equal in magnitude and opposite in phase, and wherein a portion of the surface acoustic waves generated by the first input transducer that are reflected by the first reflector and are received by the first output transducer are combined with a portion of the surface acoustic waves generated by the second input transducer that are reflected by the third reflector and are received by the second output transducer and a portion of the surface acoustic waves generated by the first input transducer that are reflected by the second reflector and are received by the first output transducer are combined with a portion of the surface acoustic waves generated by the second input transducer that are reflected by the fourth reflector and are received by the second output transducer, and wherein a portion of the surface acoustic waves generated by the first input transducer and directly received by the first output transducer are cancelled by a portion of the surface acoustic waves generated by the second input transducer and directly received by the second output transducer.

A surface acoustic wave (SAW) reflective filter for filtering an electrical input signal, said filter comprising:

• a substrate;
• a first track including a first input transducer, a first output transducer and a first reflector formed on the substrate, said first input transducer being responsive to the input signal and generating surface acoustic waves that propagate along the substrate, said first output transducer being responsive to the surface acoustic waves from the first input transducer and generating an electrical output signal, said first input transducer and said first output transducer being positioned on the substrate a predetermined distance apart and said first input transducer and said first reflector being positioned on the substrate a predetermined distance apart;
• and
• a second track including a second input transducer, a second output transducer and a second reflector formed on the substrate, said second input transducer being responsive to the input signal and generating surface acoustic waves that propagate along the substrate, said second output transducer being responsive to the surface acoustic waves from the second input transducer and generating an electrical output signal, said second input transducer and said second output transducer being the same distance apart as the first input transducer and the first output transducer, and said second input transducer and said second reflector being the same distance apart as the first input transducer and the first reflector.