Surface acoustic wave resonator, surface acoustic wave oscillator, and surface acoustic wave module unit

A surface acoustic wave resonator in which an IDT including electrode fingers for exciting surface acoustic waves is disposed on a piezoelectric substrate,

• wherein a line occupying ratio is defined as a value obtained by dividing the width of one electrode finger of the electrode fingers by the distance between a center line of a gap between the one electrode finger and the electrode finger adjacent to one side thereof and a center line of a gap between the one electrode finger and the electrode finger adjacent to the other side thereof,
• wherein the line occupying ratio causing the maximum electromechanical coupling coefficient and the line occupying ratio causing the maximum reflection of the surface acoustic waves in the IDT are different from each other,
• wherein the center of the IDT has the line occupying ratio causing an increase electromechanical coupling coefficient in comparison with the edges of the IDT,
• wherein the edges of the IDT have the line occupying ratio causing an increase in reflection of the surface acoustic waves in comparison with the center of the IDT,
• wherein an electrode finger pitch which is the distance between the centers of the neighboring electrode fingers in the IDT gradually increases from the center of the IDT to both edges thereof, and
• wherein a ratio PTs/PT of the electrode finger pitch PTs at the edges ofthe IDT to the electrode finger pitch PT at the center of the IDT is in the range of 1<PTs/PT<1.0355.