A surface acoustic wave device with three transducers and with one or two apodized converters having a minimum phases - and maximum phases pulse again administration characteristic of the ion.

摘要

PURPOSE:To improve the filter characteristic of the outside of a band by placing three electrodes containing an apodized electrode in specified positions, and using the minimum phase finite length impulse response approximation for the apodized electrode. CONSTITUTION:Receiving electrodes 12, 13 having a normal type electrode are placed on both sides of a transmitting electrode 11 having an apodized electrode using a zero point arrangement in the minimum phase finite length impulse response approximation. The transmitting electrode 11 sends out surface acoustic waves 14, 15. The surface wave 14 has the minimum phase filter characteristic, and reaches the electrode 12. Also, the surface wave 15 has the maximum phase filter characteristic, and reaches the electrode 13. In this case, phase distances 16, 17 of the electrode 11 and the electrodes 12, 13 are equal. Therefore, by connecting electrically the electrodes 12, 13, and constituting a three transducer type filter, a loss in a passing area of an output is improved. The out-band characteristic becomes the sum of the attenuation quantities of the maximum phase and the minimum phase filters, and the filter characteristic is improved.