| 摘要 |
PURPOSE:To suppress the increase of the side lobe, by having coexistence of electrodes of single structure and double structure to form reed-screen type elecrodes and at the same time varying partially the ratio of coexistance to change the surface reflection coefficient and to control the internal reflection. CONSTITUTION:Reed-screen type electrodes 43 and 44 are provided on the surface of a piezoelectric substrate 40 so that they are opposite to each other centering on a virtual axis O1-O2. For the electrode set at the part near each of electrode 43 and 44, electrodes 46 and 47 of double structure having two pairs of electrode fingers in a wavelength are provided. In this case, the ratio is increased for the electrodes of signal sturcture having a pair of electrode fingers in a wavelength toward the circumference area. In addition, the double structures are mixed sparsely among single structures at the circumference are a near the axis O1-O2, and only single structures are provided at the circumference area far from the axis O1-O2 respectively. |
