| 摘要 |
PROBLEM TO BE SOLVED: To obtain a transversal SAW filter which is miniaturized and also reduces group delay time deviation by making the transmission characteristics of one IDT electrode a wider band than those of the other IDT electrode. SOLUTION: An IDT electrode 2 and an IDT electrode 3 are arranged on the principal plane of a piezoelectric substrate 1 at a prescribed interval along the propagating direction of a surface wave. The electrodes 2 and 3 respectively comprises a pair of electrodes, having plural electrode fingers which are inserted into each other, the electrode 2 is made an apodized electrode and the electrode 3 is made a standard type. The number of electrode pairs of the electrode 3 on an output side is made small, the frequency arrangement of a 1st pole in transmission characteristics is separated from a center frequency, and the transmission characteristics of the electrode 3 is made wider band than those of the electrode 2. In the electrode 2 on an input side the cross length of a main lobe, 1st and 2nd side lobes is appropriately set to compensate the roundness on both sides of a passband in transmission characteristics.
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