Piezoelectric acoustic surface wave filter coupler

摘要

An acoustic surface wave filter comprises an input and output acoustic surface wave transducers arranged on a piezoelectric substrate in spaced acoustic channels and a coupling element for the acoustic channels of the input and output transducers, said element being arranged on the same substrate. The coupling element includes three rows of electrodes, two of which are located respectively in the acoustic channels of the input and output transducers while the third one is positioned therebetween. Each row has two groups of electrodes. The electrodes of the rows disposed in the acoustic channels of the input and output transducers are arranged in parallel to the electrodes of its transducer. The electrodes of one of the groups of these rows are interconnected through a current conducting bus. The electrodes of the third row are arranged in parallel to each other so that they have overlapping portions of a variable length defined by a specified impulse response of the filter and are directly connected to the electrodes of the other groups of rows disposed respectively in the acoustic channels. The distance between the longitudinal axes of the adjacent electrodes of the third row differs from the distances between the longitudinal axes of the adjacent electrodes of the other two rows.