| 摘要 |
PURPOSE:To obtain a characteristic suitable for a given specification by using different length for double electrode fingers of the same polarity of a weighted electrode at each pair in a range smaller than a gap between each finger pair and a dummy electrode finger and selecting said gap to a value within a specific range so as to suppress a spurious surface acoustic wave. CONSTITUTION:The group delay flatness is made almost flat where an aperture length 7 is lambda, a weighted pair number is 8.5 pairs and the center 7 of each crossing part is on the center line of the propagating axis in the effect to diffraction of a surface acoustic wave on the group delay characteristic, but the group delay characteristic is disturbed largely in taking the unnecessary crossing with the dummy electrode finger into cinsideration. On the other hand, when the gap LG with the dummy electrode finger is 0.2lambda and the length of adjacent electrode fingers is made different by 0.4LG, a value DELTAl is <=0.71lambda, no unnecessary crossing is caused and the deterioration of the group delay characteristic is effected by the diffraction only. Further, the surface acoustic wave is stimulated independently of the length of the LG in the relation between said gap LG and the group delay flatness and tee deterioration in the group delay charactristic is incurred. Thus, it is necessary to suppress the group delay flatness as <=20 ns p-p with the gap LG between 0.1lambda-0.26lambda. |
