ACOUSTIC SURFACE WAVE TRANSDUCER WITH IMPROVED INBAND FREQUENCY CHARACTERISTICS

摘要

An acoustic surface wave transducer with a transmission interdigital electrode (2A) and a reception interdigital electrode (2B in FIG. 10A-D) on a piezoelectric surface (1) has been improved by reducing inband dispersion of frequency characteristics by providing an edge effect canceler (k1), which cancels an undesired surface wave (E-a, E-b) generated at the external edge of the extreme end finger of the interdigital electrodes. Said edge effect canceler is constructed so that the length of the extreme end finger (11a) of the interdigital electrode (10, 20 in FIG.5A) is half of the length of the second extreme end finger (12a) of said interdigital electrode, and the spacing between said extreme end finger and the second extreme end finger is 1/2 wavelength of the acoustic surface Wave. Thus, the phase of the undesired surface wave generated by the extreme end finger of the transmission interdigital electrode is opposite to that generated by the second extreme end finger at the reception side, and the strength of the former is the same as that of the latter. Thus, those surface waves are cancelled by each other at the reception side, and the inband deviation or dispersion in amplitude characteristics and/or group delay characteristics of the transducer is improved.