Surface acoustic wave resonator

A two-port surface acoustic wave resonator of the type having a pair of surface acoustic wave reflectors which are spaced apart from each other by a suitable distance on a piezoelectric substrate and each of which comprises a grating electrode structure and a periodic array of grooves and two surface acoustic wave transducers which are interposed between said two surface acoustic wave reflectors and each of which comprises an interdigital electrode structure and a periodic array of grooves, characterized in that

• the electrode periodic L.sub.T of the surface acoustic wave transducers and the electrode period L.sub.R of the surface acoustic wave reflectors are so selected as to satisfy the following equation:
• ##EQU14## where C.sub.1T :
• the acoustic mismatching term at the boundary between the electroded portion and the non-electroded portion of the surface acoustic wave transducer and is given by
• C.sub.1T =.vertline.1-Z.sub.2 /Z.sub.1 .vertline./.pi.
• where
• Z.sub.2 :
• the acoustic impedance of the electroded portion, and
• Z.sub.1 :
• the acoustic impedance of the non-electroded portion;
• C.sub.2T :
• the relative frequency decrease due to the periodic structure of the surface acoustic wave transducer;
• C.sub.2R :
• the relative frequency decrease due to the periodic structure of the surface acoustic wave reflector;
• and
• q.sub.T =.pi.C.sub.1T N
• where N:
• the number of electrode finger pairs in each of the surface acoustic wave transducers.

A surface acoustic wave resonator characterized in that

• the electrode period L.sub.T of a surface acoustic wave transducer and the electrode period L.sub.R of a surface acoustic wave reflector or surface acoustic wave reflectors are so selected as to satisfy the following equation:
• ##EQU16## where C.sub.1T :
• the acoustic mismatching term at the boundary between the electroded portion and the non-electroded portion of the surface acoustic wave transducer and is given by
• C.sub.1T =.vertline.1-Z.sub.2 /Z.sub.1 .vertline./.pi.
• where
• Z.sub.2 :
• the acoustic impedance of the electroded portion, and
• Z.sub.1 :
• the acoustic impedance of the non-electroded portion;
• C.sub.2T :
• the relative frequency decrease due to the periodic structure of the surface acoustic wave transducer;
• C.sub.2R :
• the relative frequency decrease due to the periodic structure of the surface acoustic wave reflector;
• and
• q.sub.T =.pi.C.sub.1T N
• where N:
• the number of electrode finger pairs in the surface acoustic wave transducer;
• a pair of terminals are attached substantially at the midpoints of the longer sides, respectively, of a piezoelectric substrate upon which said surface acoustic wave reflectors and transducer are formed and are electrically connected to said surface acoustic wave transducer;
• lead wires extended from a base are electrically joined to said pair of terminals, respectively, whereby said piezoelectric substrate is supported at two points by said lead wires;
• and
• said piezeoelectric substrate and said pair of lead wires are encapsulated in a case which in turn is sealed air-tightly with said base.