High selectivity SAW DMS filter with in-between shorted-gratings

A new structure is proposed to improve the selectivity of SAW DMS filter. Shorted-gratings are inserted between the input and output IDTs as additional reflectors which are designed to have a stopband at the frequencies just higher than the passband of the filter. The waves from input IDT to output IDT at the frequencies within the stopband of the in-between grating are strongly reflected, so the attenuation in the high frequency transition band of the filter can be drastically increased. Combining this novel structure with the concept of pitch-modulated IDT and reflector, and using effective global optimization algorithm, DMS filter with low insertion loss, wide band and high selectivity can be designed. The in-between reflector also makes it easier to realize DMS filter with 1-2% passband width on 42°LiTO₃. The in-between reflector can be used to electrically connect busbars in layout design, thus inner bonding pads are not needed, which results in smaller chip size.