Surface acoustic wave device

1. A surface acoustic wave device having a given impedance comprising:

multimode type filters connected in series,

a composite impedance of the multimode type filters defining the given impedance of the surface acoustic wave device,

wherein each of the multimode type filters has multiple interdigital transducers (IDTs), and corresponding IDTs of the multimode type filters among the multiple IDTs are separately connected in series.

2. The surface acoustic wave device as claimed in claim 1 , wherein the given impedance is equal to a characteristic impedance of a transmission line to which the surface acoustic wave device is connected.

3. The surface acoustic wave device as claimed in claim 1 , wherein each of the multimode type filters has multiple interdigital transducers (IDTs), and corresponding IDTs of the multimode type filters among the multiple IDTs are connected in series by common bus bars, which have tapered ends.

4. The surface acoustic wave device as claimed in claim 1 , wherein the multimode type filters have different electrostatic capacitances.

5. The surface acoustic wave device as claimed in claim 1 , wherein the multimode type filters have different aperture lengths.

6. The surface acoustic wave device as claimed in claim 1 , wherein the multimode type filters include a first multimode type filter to which an input terminal of the surface acoustic wave device is connected, and a second multimode type filter to which an output terminal of the surface acoustic wave device is connected.

7. The surface acoustic wave device as claimed in claim 1 , wherein the multimode type filters includes a first multimode type filter to which one of input and output terminals of the surface acoustic wave device is connected.

8. The surface acoustic wave device as claimed in claim 1 , further comprising a plurality of groups of multimode type filters connected in parallel, wherein each of the plurality of groups of multimode type filters includes said multimode type filters connected in series.

9. The surface acoustic wave device as claimed in claim 1 , wherein one of the multimode type filters arranged on an output side of the surface acoustic wave device is cascaded to another multimode type filter.

10. The surface acoustic wave device as claimed in claim 1 further comprising a plurality of groups of multimode type filters connected in parallel, wherein each of the plurality of groups of multimode type filters includes said multimode type filters connected in series, and multimode type filters arranged on an output side of the surface acoustic wave device are cascaded to other multimode type filters.

11. The surface acoustic wave device as claimed in claim 1 , further comprising balanced input or output terminals.

12. The surface acoustic wave device as claimed in claim 1 , further comprising a piezoelectric substrate on which the multimode type filters are formed.

13. The surface acoustic wave device as claimed in claim 1 , further comprising a first filter to which one of transmitted and received signals is applied, and a second filter to which the other one is applied, wherein one of the first and second filters includes said multimode type filters.

14. The surface acoustic wave device as claimed in claim 13 , wherein the first and second filters are formed on an identical piezoelectric substrate.

15. A surface acoustic wave device having a given impedance comprising:

multimode type filters connected in series,

a composite impedance of the multimode type filters defining the given impedance of the surface acoustic wave device,

wherein:

each of the multimode type filters has multiple interdigital transducers (IDTs);

corresponding IDTs of the multimode type filters among the multiple IDTs are separately connected in series by interconnection patterns;

at least one electrode finger is arranged between electrode fingers respectively extending from adjacent interconnection patterns; and

said at least one electrode finger is at a potential different from potentials of the adjacent interconnection patterns.