Abstract: A surface acoustical wave (SAW) filter is provided by placing at least one pair resonator channels consisting of reflectors and input and output transducers on the surface of a suitable substrate, such as a piezo-electric crystal. One channel of the pair consists of an input transducer and an output transducer which are aligned in a path along which the SAW progresses. The two channels are identical except that the separation distance between the transducers and the reflectors, in one channel is slightly different than the corresponding distance in the other channel. This separation difference serves to broaden the passband for applications which require a broader passband than is obtainable with a single channel resonator filter. Differential detection of the SAW in one section with respect to the other channel is achieved by using a symetrically inverted output transducer, in one embodiment. In another embodiment an offset transducer is used to accomplish the differential sensing.

Abstract: An acoustic surface wave device is configured as a bandpass filter. The device employs two interdigital transducer pairs for input and output. Each transducer pair has a slant finger geometry. The fingers are electrodeposited into grooves etched into the substrate. The grooves are deeper at the high frequency side of the substrate. The grooves enhance the electromechanical coupling of high frequency components and thus provide a flatter amplitude response curve.