| 摘要 |
PURPOSE:To increase the equivalent coupling coefficient and thus obtain a wide pass band characteristics, by dividing the grating reflector into several pieces so that several units of the wave guide paths may be formed in parallel within the width of the aperture length of the input or output electrode. CONSTITUTION:The input and output electrodes 42 and 43 are formed on the piezoelectric substance 41 and in opposition to each other centering on the shielding electrode 44. And a pair of grating reflectors 45 and 46 are formed as if they held the electrodes 42, 43 and 44 each between. Both the strip width and the strip space are set to lambda/4 (lambda:length of surface wave) for the reflectors 45 and 46. In such case, each strip is formed discontinuously as if it were cut and divided into several pieces for the reflectors 45 and 46 the entire length of which is identical substantially to the aperture length D of the electrodes 42 and 43. As a result, the emergence of the lateral mode spuriousness can be eleminated within the pass band of the filter, accordingly decreasing the reduction of the Q value. |
