Longitudinally coupled double mode surface wave resonators

A surface wave resonator comprising:

• a piezoelectric substrate;
• two reflectors, two lateral IDTs (inter-digital transducers), and a centre IDT arranged on a surface of the substrate, with the IDTs between the two reflectors and with the centre IDT between the two lateral IDTs for coupling surface waves between the IDTs, the two lateral IDTs being substantially symmetrical about the centre IDT, each IDT having interleaved fingers extending from two rails for providing connections to the IDT;
• a single ended connection to a first rail of the centre IDT;
• a differential signal connection to the two lateral IDTs, the differential signal connection comprising a connection to a first rail of one lateral IDT on one side of the IDTs and a connection to a first rail of the other lateral IDT on the opposite side of the IDTs;
• and
• a ground connection to a second rail of each of the IDTs.

A surface wave resonator comprising:

• a piezoelectric substrate;
• two reflectors, two lateral IDTs (inter-digital transducers), and a centre IDT arranged on a surface of the substrate, with the IDTs between the two reflectors and with the centre IDT between the two lateral IDTs for coupling surface waves between the IDTs, each IDT having interleaved fingers extending from two rails for providing connections to the IDT, the two lateral IDTs having their fingers oppositely phased to provide opposite polarities and otherwise being substantially symmetrical about the centre IDT;
• a single ended connection to a first rail of the centre IDT;
• a differential signal connection to the two lateral IDTs, the differential signal connection comprising connections to a first rail of each lateral IDT, the first rails of the lateral IDTs being both on one side of the IDTs;
• and
• a ground connection to a second rail of each of the IDTs.

A surface wave resonator comprising:

• a piezoelectric substrate;
• two reflectors, two lateral IDTs (inter-digital transducers), and a centre IDT arranged on a surface of the substrate, with the IDTs between the two reflectors and with the centre IDT between the two lateral IDTs for coupling surface waves between the IDTs, each IDT having interleaved fingers extending from two rails for providing connections to the IDT, the two lateral IDTs having finger-to-finger spacings from the centre IDT which differ by substantially .lambda./2+m.lambda., where .lambda. is the wavelength of a SAW to be propagated and m is zero or a positive integer, the two lateral IDTs otherwise being substantially symmetrical about the centre IDT;
• a single ended connection to a first rail of the centre IDT;
• a differential signal connection to the two lateral IDTs, the differential signal connection comprising connections to a first rail of each lateral IDT, the first rails of the lateral IDTs being both on one side of the IDTs;
• and
• a ground connection to a second rail of each of the IDTs.

A longitudinally coupled double mode surface wave resonator comprising:

• a piezoelectric substrate;
• and
• two reflectors, two lateral IDTs (inter-digital transducers), and a centre IDT arranged on a surface of the substrate, with the IDTs between the two reflectors and with the centre IDT between the two lateral IDTs so that surface waves are coupled between the IDTs, each IDT having interleaved fingers extending from rails for providing connections to the IDT;
• wherein the centre IDT and at least one of its rails is divided into two halves arranged to operate with opposite signal phases with a balanced signal connection thereto.