Surface acoustic wave filter utilizing a particularly placed spurious component of a parallel resonator

A surface acoustic wave filter comprising:

• a surface acoustic wave substrate;
• a series resonator disposed on the surface acoustic wave substrate and having a resonant frequency and an antiresonant frequency, the series resonator being arranged to define a series arm;
• and
• at least one parallel resonator disposed on the surface acoustic wave substrate having a resonant frequency and an antiresonant frequency which is substantially identical to the resonant frequency of the series resonator, the at least one parallel resonator being arranged to define a parallel arm, the series arm and the parallel arm defining a ladder circuit such that the surface acoustic wave filter has a predetermined pass band;
• wherein
• the at least one parallel resonator has a spurious component at a frequency located between the resonant frequency of the at least parallel resonator and a low end of the passband of the surface acoustic wave filter or at a frequency located between the antiresonant frequency of the series resonator and a high end of the passband of the surface acoustic wave filter.

A ladder type filter comprising:

• a surface acoustic wave substrate;
• a series resonator disposed on the surface acoustic wave substrate and being arranged to define a series arm;
• and
• at least one parallel resonator disposed on the surface acoustic wave substrate and being arranged to define a parallel arm, the series arm and the parallel arm defining a ladder circuit such that the surface acoustic wave filter has a predetermined pass band;
• wherein
• the at least one parallel resonator has a spurious component at a frequency located between a resonant frequency of the at least one parallel resonator and a low end of the passband of the surface acoustic wave filter or at a frequency located between an antiresonant frequency of the series resonator and a high end of the passband of the surface acoustic wave filter.