Abstract: A longitudinally coupled resonator type surface acoustic wave filter having a balance-unbalance conversion function achieves improved amplitude balance and phase balance. The surface acoustic wave filter includes first, second and third IDTs. The second IDT is positioned in the center of the three IDTs and has an even number of electrode fingers. The polarity of the electrode finger of the first IDT adjacent to the second IDT is opposite to the polarity of the electrode finger of the third IDT adjacent to the second IDT.

Abstract: A surface acoustic wave filter includes at least two series arm surface acoustic wave resonators provided in an series arm and at least one parallel arm surface acoustic wave resonator provided in a parallel arm. At least one of the series arm surface acoustic wave resonators has a plurality of anti-resonant points and a sub-resonant point located between the anti-resonant points. The sub-resonant point substantially matches an anti-resonant point of at least one of the remaining series arm surface acoustic wave resonators.

Abstract: A surface acoustic wave device includes a piezoelectric substrate, at least one IDT disposed on the piezoelectric substrate, and an input end and an output end connected to the IDT. At least one of the input end and the output end includes a pair of balanced signal terminals, and a delay line or a reactance component connected to one of the pair of balanced signal terminals.

Abstract: A surface acoustic wave device includes a first surface acoustic wave filter connected between an input terminal and an output terminal, a second surface acoustic wave filter having a different center frequency from that of the first surface acoustic wave filter, and which is connected between the input terminal and the output terminal and in parallel with the first surface acoustic wave filter, and at least one one-port surface acoustic wave resonator connected in series with the first or second surface acoustic wave filter, on at least one side between the input terminal and at least one of the first and second surface acoustic wave filters, or between the output terminal and at least one of the first and second surface acoustic wave filters.