A surface acoustic wave includes a surface acoustic wave element including a piezoelectric substrate having IDTs, input/output terminals, and reference potential terminals provided thereon and a package enclosing the surface acoustic element and having electrode lands and external terminals. The resonance frequency of the resonator defined by inductances generated by the reference potential terminals of the external terminals of the package, is positioned in the vicinity of an image frequency occurring at a time of performing frequency conversion in a super heterodyne system.
A surface acoustic wave device includes first and second SAW filters and first, second and third SAW resonators. The first SAW filter has first and second ends and a first pass band in a first frequency region, and the second SAW filter has first and second ends and a second pass band in a second frequency region which is lower than the first frequency region. The second end of the second SAW filter is connected to the second end of the first SAW filter in parallel to form a connection point. The first and second one-port SAW resonators are connected in series between the second end of the first SAW filter and the connection point, and have an antiresonant frequency higher than the frequency of the pass band of the first SAW filter. The third one-port SAW resonator connected in series between the second end of the second SAW filter and the connection point and has an antiresonant frequency higher than the frequency of the pass band of the second SAW filter.
A surface acoustic wave apparatus includes first and second longitudinally-coupled resonator filters disposed on a surface-wave board. In each longitudinally-coupled resonator filter, the ground electrodes of IDTs disposed at opposite sides of the center IDT and adjacent to reflectors are connected to different ground electrodes located on the same layer in the package, with at least two bonding wires.
A surface acoustic wave device has a structure in which first and second filters are connected in parallel at a connection point connected to an input terminal or an output terminal. The surface acoustic wave device includes the first SAW filter having a capacitive impedance in a passband of the second SAW filter and having a higher passband than the second SAW filter and the second SAW filter having a capacitive impedance in the passband of the first SAW filter and having a lower passband than the first SAW filter. The second SAW filter is connected in parallel at the connection point on the input terminal or output terminal side of the first SAW filter. The impedance of the first SAW filter in the passband at the parallel-connected end has, before parallel connection, a resistance component of about 1.2 Z.sub.0 or higher with respect to the characteristic impedance Z.sub.0 of the device, and is higher than the impedance of the second SAW filter in the passband at the parallel-connected end thereof.
A surface acoustic wave device which not only is low-loss in a pass band and has high attenuation in an attenuation region but also has superior power-resistance and has a large reflection coefficient in a blocking region comprises a first one-port SAW resonator filter connected in parallel with a three-electrode vertically connected double mode SAW resonator filter. The first one-port SAW resonator filter is so constructed that its resonance frequency is outside the pass band of the vertically connected double mode SAW resonator filter on the low-frequency side thereof and a connection point between the double mode SAW resonator filter and the first one-port SAW resonator filter is provided to an input terminal.