Patent ID: 6853269
Filing Date: 2005-02-08
Classification: H03H

Abstract:
1. A surface acoustic wave filter comprising: a piezoelectric substrate; at least an input IDT electrode arranged on said piezoelectric substrate; and at least an output IDT electrode arranged on said piezoelectric substrate, wherein said surface acoustic wave filter is a longitudinally coupled mode surface acoustic filter and includes said input IDT electrode and said output IDT electrode disposed within a single propagation path in which a surface acoustic wave propagates, said input IDT electrode has a plurality of electrode fingers pitches; of the electrode fingers pitches of said input IDT electrode, an electrode fingers pitch having the most pairs of electrode fingers is defined as a main input pitch, said output IDT electrode has a plurality of electrode fingers pitches, of the electrode fingers pitches of said output IDT electrode, an electrode fingers pitch having the most pairs of electrode fingers is defined as a main output pitch, the main input pitch of electrode fingers of said input IDT electrode and the main output pitch of electrode fingers of said output IDT electrode are different from each other, the main pitch of electrode fingers of the IDT electrode larger in number of electrode fingers in said input and output IDT electrode is larger than the main pitch of electrode fingers smaller in number of electrode fingers, and one of said input IDT electrode and said output IDT electrode comprises first IDT electrode each including a pair of electrode fingers opposed to each other; the other of said input IDT electrode and said output IDT electrode comprises second and third IDT electrodes each including a pair of electrode fingers opposed to each other; said second IDT electrode is placed on one side of said first IDT electrode; said third IDT electrode is placed on the other side of said first IDT electrode; said first, second, and third IDT electrodes are arranged along a direction in which a surface acoustic wave propagates; and the peak frequency of the radiation characteristic of said first IDT electrode and at least one of said second and third IDT electrode are substantially equal to each other.