Surface acoustic wave filter and duplexer using same

A surface acoustic wave filter, comprising:

• a piezoelectric substrate;
• a surface acoustic wave element comprising a first IDT electrode on the piezoelectric substrate;
• a first signal line electrically connected to the first IDT electrode;
• a ring-shaped reference potential line which comprises a first intersecting portion intersecting with the first signal line through a first insulation member and surrounds the surface acoustic wave element;
• a second signal line,
• wherein
• the surface acoustic wave element further comprises a second IDT electrode which is located next to the first IDT electrode along a direction in which a surface acoustic wave of the surface acoustic wave element propagates, and is electrically connected to the second signal line,
• the reference potential line further comprises a second intersecting portion which intersects with the second signal line through a second insulation member,
• the first IDT electrode comprises a first signal bus bar conductor connected to the first signal line and a first reference potential bus bar conductor electrically connected to the reference potential line, and
• the second IDT electrode comprises a second signal bus bar conductor connected to the second signal line and a second reference potential bus bar conductor electrically connected to the reference potential line;
• a third signal line,
• wherein
• the surface acoustic wave element further comprises a third IDT electrode which is located along the direction and is electrically connected to the third signal line,
• the reference potential line further comprises a third intersecting portion which intersects with the third signal line through a third insulation member,
• the third IDT electrode comprises a third signal bus bar conductor connected to the third signal line and a third reference potential bus bar conductor electrically connected to the reference potential line,
• the first IDT electrode is between the second IDT electrode and the third IDT electrode, and
• when dividing an inside of a ring of the reference potential line into a first region and a second region along the direction, the first signal bus bar conductor, the second reference potential bus bar conductor, and the third reference potential bus bar conductor are in the first region, and the first reference potential bus bar conductor, the second signal bus bar conductor, and the third signal bus bar conductor are in the second region;
• an unbalanced signal terminal electrically connected to the first signal line;
• a first balanced signal terminal electrically connected to the second signal line;
• and a second balanced signal terminal electrically connected to the third signal line;
• and
• a branched line which is located between the second signal line and the third signal line, and is connected to the reference potential line.

A surface acoustic wave filter, comprising:

• a piezoelectric substrate;
• a surface acoustic wave element comprising
• a plurality of IDT electrodes which are located on the piezoelectric substrate and along a direction in which a surface acoustic wave propagates;
• a plurality of signal lines electrically connected to the plurality of IDT electrodes;
• a ring-shaped reference potential line which comprises a plurality of intersecting portions intersecting with the plurality of signal lines through a plurality of insulation members and surrounds the surface acoustic wave element;
• and
• a SAW resonator which is located at one side of the surface acoustic wave element in a direction perpendicular to the direction in which the surface acoustic wave propagates and is located outside of the ring-shaped reference potential line, wherein
• the plurality of insulation members include, at the one side of the surface acoustic wave element, two or more insulation members which are located along the direction in which the surface acoustic wave propagates and are separated from each other in that direction,
• the ring-shaped reference potential line touches the piezoelectric substrate among the two or more insulation members.