Surface acoustic wave (SAW) resonator SAW filter and SAW antenna duplexer using the SAW resonator

A surface acoustic wave (SAW) resonator comprising:

• a piezoelectric substrate;
• an interdigital transducer (IDT) electrode formed on said piezoelectric substrate;
• and
• a reflector electrode adjacent to said IDT electrode,
• wherein said IDT electrode comprises a plurality of first finger-electrodes, a plurality of second finger electrodes, a plurality of strip-line electrodes, a first bus-bar electrode, and a second bus-bar electrode;
• wherein said first finger-electrodes and said second finger-electrodes do not overlap with each other, but are acoustically coupled together by said strip line electrodes,
• wherein the first finger-electrodes are coupled to said first bus-bar electrode;
• wherein the second finger-electrodes are coupled to said second bus-bar electrode;
• wherein the strip-line electrodes are disposed at positions for exciting surface acoustic waves between said first bus-bar electrode and said second bus-bar electrode,
• wherein said strip-line electrodes include a plurality of first strip-line electrodes to a plurality of N-th strip-line electrodes, N being an integer of 2 or more,
• wherein a portion of said first strip-line electrodes is disposed so as to overlap with said first finger-electrodes at a position deviated by λ/2 from the center of said first finger-electrodes, λ being a propagation wavelength of a surface acoustic wave,
• wherein a portion of said N-th strip-line electrodes is disposed so as to overlap with said second finger-electrodes at a position deviated by λ/2 from the center of said second finger-electrodes, λ being the propagation wavelength of a surface acoustic wave,
• wherein said first strip-line electrodes to said N-th strip-line electrodes are sequentially arranged to overlap mutually at a specified length,
• wherein said IDT electrode and said reflector electrode adjacent thereto constitute N+1 resonator units, and
• wherein said resonator units are connected in series by way of said strip-line electrodes,
• wherein said N+1 resonator units are different in resonance frequency at least between adjacent resonator units, and are coupled acoustically by said strip-line electrodes.