| 摘要 |
PURPOSE:To prevent an influence of reflection in a passing band between fixed frequencies f1 and f2, by slightly varying electrode finger width where reflection of input and output in a combtooth-shaped electrode is caused. CONSTITUTION:An elastic wave of waveform (lambda) and speed (v) propagating on the surface of a piezoelectric substrate is partially reflected at the front and back edges of the electrode finger of width (d) and when (d) is equal to lambda/4, both waves strengthen each other. At this time, frequency (f) is v/DELTAd and if this frequency resides in a passing band, a characteristic value decreases. For the purpose, electrode widths d1=v/DELTAf1 and d2=DELTA/DELTAf2 are determined corresponding to frequencies f1 and f2; and the width corresponding to frequencies in the passing band is independently corrected slightly and the finger-width distribution of the electrode is corrected on the whole, so that an influence of the reflected wave can be prevented. At this time, the number of fingers of width (d) less than d2 and greater than d1 should be 20% or less and the individual finter width corrected on the whole should be 50% or less, so that a weighted electrode working in the UHF band with a little intra-electrode reflection can be obtained. |
