UHF Multilayer Acoustic Filter.
Technical rept. 21 Dec 67-21 Jul 68,
STANFORD RESEARCH INST MENLO PARK CA
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The theoretical design of a multilayer acoustic filter is described. A prototype design that uses a minimum number of gold and aluminum films and cadmium sulphide input and output transducers is analyzed and is found to have a 3-dB bandwidth on the order of one percent and insertion loss on the order of 20 dB. To overcome this insertion loss, a transistor amplifier is added in series with the filter. Analysis of both field-effect and bipolar transistors shows that, if no external tuning or impedance matching is allowed, the bipolar transistor is superior. A method is described for measuring the change in amplitude of an acoustic wave as it is reflected from the end of a sapphire rod that is being coated with a metal film or films. The magnitude of the acoustic losses can be inferred from these data. It appears that gold and aluminum films with acoustic Qs of several hundred can be realized, but the measurements are not yet complete enough to be conclusive. A physical design for a 500-MHz prototype filter and the procedure for fabricating such a filter are described. Author