Optimisation of weighted SAW grating reflectors with minimised time delay deviation

This paper discusses a method of designing weighted SAW grating reflectors which enables one to develop the filters having a small group delay deviation, a flat passband and steep responses in transition bands. Both electrode width and withdrawal-weightings were adopted to realise weighted reflectors. An SAW delay line employing the optimally designed reflector was fabricated, and the reflector performance was discussed. The group delay deviation of less than 80 ns in the stopband was achieved at the centre frequency of 200 MHz. For practical applications, an SAW IF filter employing the reflectors was fabricated. The reflector response is vividly reflected on filter performance, achieving the group delay deviation of less than 80 ns in the passband.