Surface Wave Narrow Band Resonators.
Interim technical rept. 30 Jun-31 Dec 75,
RAYTHEON CO WALTHAM MASS RESEARCH DIV
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Measurements have been made on numerous types of reflective gratings to determine the phase of the reflection and to find methods of getting high reflectivity per stripe. A new form of grating consisting of gold stripes recessed in ion-etched grooves has been found to have a very high reflection coefficient per stripe. Novel fabrication techniques for this type of grating are discussed. It has been concluded that the goals of this program of very low insertion loss, high out-of-band rejection and large for a resonator bandwidth cannot be achieved simultaneously with conventional SAW resonators. Therefore, a new type of device called a ring filter has been developed and studied. Like a resonator it confines virtually all of the acoustic energy with highly reflecting gratings. However, since tightly coupled transducers are used, very little energy makes more than one transit around the ring. It is therefore not truly resonant except as a degenerate case of resonance. The geometry is such, however, that the transducers cannot transmit to each other when the gratings become transparent. This provides very high out-of-band rejection without the sacrifice of other needed device characteristics as with conventional SAW resonator geometries. The properties of several ring filters, which have been built, are discussed. The goals of 2 dB insertion loss, 60 dB out-of-band rejection, and 2 percent bandwidth appear to be within the capability of this type of device. Author
- Line, Surface and Bulk Acoustic Wave Devices