SAW filters including one-focus slanted finger interdigital transducers

The present paper describes a new SFIT-filter type (SFIT: Slanted Finger Interdigital Transducer) that allows fast analysis as a precondition for fast optimization. Therefore, filter structure and analysis are especially suitable for optimizing Unidirectional SFIT (USFIT) filters. For analysis, a SFIT filter is usually divided into many narrow channels. Every channel is considered to be a subfilter and is analyzed separately. Therefore, the total filter analysis is very time consuming. For reducing computing time, we suggest a one-focus structure. As a result, the parameters of all subfilters can be calculated from the parameters of only one subfilter by simple frequency scaling. However, one-focus SFIT filters with continuous finger edges show a deep minimum within the passband. This problem can be overcome by using stepped one-focus structures.