Surface Wave Narrow Band Resonators.
Abstract
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. On LiNbO3 an insertion loss of 2.5 dB has been achieved with a 3 dB bandwidth of 1.4 percent. Out-of-band rejection is better than 60 dB. On ST-cut quartz an insertion loss of 4 dB has been obtained along with a 2.3 percent bandwidth. Again out-of-band rejection is better than 60 dB. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1976
- Accession Number
- ADA030139
Entities
People
- F. Sandy
- T. E. Parker
Organizations
- RTX