Longitudinally coupled resonator type surface acoustic wave filter

A longitudinally coupled resonator type surface acoustic wave filter comprising:

• a piezoelectric substrate;
• and
• first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers;
• wherein
• the first and second IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other;
• the second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the second and third IDTs adjacent to each other;
• and
• a number of the electrode fingers of the narrow electrode-finger pitch sections in the first and second IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the second and third IDTs.

A longitudinally coupled resonator type surface acoustic wave filter comprising:

• a piezoelectric substrate;
• and
• first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers;
• wherein
• only the first and second IDTs or only the second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other, or at the respective end portions of the second and third IDTs adjacent to each other.

A longitudinally coupled resonator type surface acoustic wave filter comprising:

• a piezoelectric substrate;
• a first longitudinally coupled resonator type surface acoustic wave filter unit which includes first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers;
• a second longitudinally coupled resonator type surface acoustic wave filter unit which includes fourth, fifth and sixth IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the fifth IDT is interposed between the fourth and the sixth IDTs, each of the fourth, fifth and sixth IDTs having a plurality of electrode fingers;
• wherein
• the first, second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first, second and third IDTs adjacent to each other;
• the fourth, fifth and sixth IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the fourth, fifth and sixth IDTs adjacent to each other;
• and
• the electrode-finger pitch of the narrow electrode-finger pitch sections in the first, second and third IDTs is different from the electrode-finger pitch of the narrow electrode-finger pitch sections in the fourth, fifth and sixth IDTs.

A longitudinally coupled resonator type surface acoustic wave filter comprising:

• a piezoelectric substrate;
• a first longitudinally coupled resonator type surface acoustic wave filter unit which includes first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers;
• a second longitudinally coupled resonator type surface acoustic wave filter unit which includes fourth, fifth and sixth IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the fifth IDT is interposed between the fourth and the sixth IDTs, each of the fourth, fifth and sixth IDTs having a plurality of electrode fingers;
• wherein
• the first, second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first, second and third IDTs adjacent to each other;
• the fourth, fifth and sixth IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the fourth, fifth and sixth IDTs adjacent to each other;
• and
• a number of the electrode fingers of the narrow electrode-finger pitch sections in the first, second and third IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the fourth, fifth and sixth IDTs.

A longitudinally coupled resonator type surface acoustic wave filter comprising:

• a piezoelectric substrate;
• a first longitudinally coupled resonator type surface acoustic wave filter unit which includes first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTS, each of the first, second and third IDTs having a plurality of electrode fingers;
• a second longitudinally coupled resonator type surface acoustic wave filter unit which includes fourth, fifth and sixth IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the fifth IDT interposed between the fourth and the sixth IDTs, each of the fourth, fifth and sixth IDTs having a plurality of electrode fingers;
• wherein
• only the first, second and third IDTs or only the fourth, fifth and sixth IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch that is narrower than the remaining electrode-finger pitches, at respective end portions of the first, second and third IDTs adjacent to each other, or at respective end portions of the fourth, fifth and sixth IDTs adjacent to each other.