a matched filter has an input idt and an output idt , and also has a device for preventing propagating surface acoustic waves from diverging . by preventing the divergence of surface acoustic waves , signals obtained in units of electrode finger pairs of the output idt are uniformed . furthermore , this application also discloses the following arrangement . that is , an arrangement for converging surface acoustic waves is adopted , and the width of surface acoustic waves input to the output idt is set to be larger than at least the crossing width of electrode fingers , nearest to the input idt , of those of the output idt , so that some surface acoustic waves propagate along non - crossing portions of the electrode fingers , on the input idt side , of those of the output idt . with this arrangement , the influence of the crossing portions of the electrode fingers , closer to the input idt , on the surface acoustic waves input to the crossing portions of the electrode fingers , farther from the input idt , can be relaxed .