An SAW filter employing weighted reflectors and a multi-strip coupler

This paper deals with a miniaturised surface acoustic wave (SAW) filter employing two IDTs, two weighted reflectors and a multi-strip coupler (MSC). In the structure, the width-weighted reflectors are to be responsible for the frequency response of the filter. The reflectors are optimally designed to realise the specified frequency response by taking account of the SAW reflectivity of width-weighted electrodes. The filter having 3 dB bandwidth of 4.0 MHz was designed at the centre frequency of 200 MHz and fabricated on 128/spl deg/ YX-LiNbO/sub 3/. The total acoustic length of the filter was reduced to less than 5 mm. The experimental result obtained was in good agreement with the theoretical prediction.