ELASTIC WAVE FILTER, DUPLEXER USING THE ELASTIC WAVE FILTER, AND COMMUNICATION EQUIPMENT USING THE DUPLEXER

摘要

There is provided an elastic wave filter which exhibits superior steepness without addition of external components or new manufacturing steps. On the same substrate, a plurality of filters (10-1) are provided each of which has a first resonator (2a-1) arranged on a serial arm, where a resonant frequency is frs and an antiresonant frequency is fas, and a second resonator (4a-1) arranged on a parallel arm, where a resonant frequency is frp and an antiresonant frequency is fap, wherein the resonant frequency frs of the first resonator is higher than the resonant frequency frp of the second resonator, while the antiresonant frequency fas of the first resonator is higher than the antiresonant frequency fap of the second resonator. At least one of the multistage-connected filters (10-1) has a third resonator (6-1), where a resonant frequency is frp and an antiresonant frequency is fap. The third resonator (6-1) is formed on the substrate, and is connected to the serial arm in parallel with the first resonator (2a-1).