SAW filter with an improved attenuation characteristic at a frequency any multiple of an attenuation pole frequency at one or both sides of a pass band

A constant K SAW filter comprising:

• a plurality of serial arm resonators and a plurality of parallel arm resonators interconnected in pairs in a multiple-stage, ladder configuration;
• and
• a resonating device serially connected to any one of said plurality of serial arm resonators and having an attenuation pole frequency higher than an attenuation pole frequency of said serial arm resonator, said resonating device functioning, at the attenuation pole frequency of said serial arm resonator, as a capacitance without performing substantial attenuation;
• said resonating device having an antiresonance frequency that is any multiple of an antiresonance frequency of said serial arm resonator.

A constant K SAW filter comprising:

• a plurality of serial arm resonators and a plurality of parallel arm resonators interconnected in pairs in a multiple-stage, ladder configuration;
• and
• a resonating device connected to any one of said plurality of parallel arm resonators in parallel and having an attenuation pole frequency higher than an attenuation pole frequency of said parallel arm resonator, said resonating device functioning, at the attenuation pole frequency of said parallel arm resonator, as a capacitance without performing substantial attenuation;
• said resonating device having a resonance frequency 1.8 times or above but 2.2 times or below, or 2.7 times or above but 3.3 times or below, as high as a resonance frequency of said parallel arm resonator.

A constant K SAW filter comprising:

• a plurality of serial arm resonators and a plurality of parallel arm resonators interconnected in pairs in a multiple-stage, ladder configuration;
• and
• a resonating device connected to any one of said plurality of parallel arm resonators in parallel and having an attenuation pole frequency higher than an attenuation pole frequency of said parallel arm resonator, said resonating device functioning, at the attenuation pole frequency of said parallel arm resonator, as a capacitance without performing substantial attenuation;
• said resonating device having a resonance frequency that is any multiple of a resonance frequency of said parallel arm resonator.