SURFACE ACOUSTIC WAVE FILTER

摘要

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter in which a satisfactory characteristic can be realized by increasing the number of effective impulses by securing a sufficient propagation distance regardless of a small shape. SOLUTION: An IDT 12 for input is formed at the upper part of the central part of a crystal substrate, an IDT 10 for feedback is formed at the lower part at a left side, and an IDT 14 for output whose electrode finger length is doubled is formed at a right side. The IDT 12 for input excites a surface acoustic wave in a piezoelectric substrate by an electric signal X(z) from an input port X and transmits the surface acoustic wave to the IDT 14 for output. The IDT 14 for output at the right side receives the surface acoustic wave from the IDT 12 for input and outputs an electric signal Y(z) to an output port Y. The IDT 10 for feedback excites a surface acoustic wave by the electric signal outputted from the IDT 14 for output and transmits the surface acoustic wave to the IDT 14 for output.