| 摘要 |
<p>A multi-longitudinal mode SAW filter having a flat passband characteristic. The filter has an energy-confined SAW resonator made of a frequency-rise piezoelectric substrate. An IDT is divided into a first IDT1 on the transmission side, a second IDT2 on the reception side, and the third IDT3 between the first IDT1 and IDT2 so as to control the amplitudes of vibration of the two modes S0 and A0 synthesized by the filter. The frequency potential is optimized by varying the electrode period lengths of the IDT1, IDT2, and IDT3. The resonance amplitude strengths of the S0 and A0 modes are equalized and hence the transmission characteristic of the passband is flattened. Therefore, a filter with a relatively wide bandwidth from 1000 to 1500 ppm is realized by using a substrate having a small electromechanical coupling factor such as a crystal substrate.</p> |
