Acoustic surface wave device including a reflective multistrip coupler

Claim 1

An acoustic surface wave device comprising a piezoelectric substrate for propagating an acoustic surface wave at a surface thereof, transducer means for launching acoustic surface wave energy so as to propagate over said surface and for converting acoustic surface wave energy propagating over said surface into an electrical signal, and electrical coupling means for receiving acoustic surface wave energy propagating along a first propagation track and relaunching at least part of that energy as acoustic surface wave energy along a second propagation track, said electrical coupling means comprising a first array of electrically conductive strips across said first track and a second array of electrically conductive strips across said second track, each array including discrete parallel electrically conductive strips each of which is electrically insulated from the other said discrete conductive strips of that array and is electrically connected to a respective said discrete conductive strip of the other array such that the successive said discrete conductive strips of each array are electrically connected to the successive said discrete conductive strips of the other array, the centre-to-centre spacings of the successive said discrete conductive strips of each array being alternately relatively large and relatively small, the said discrete conductive strips of the two arrays being interconnected such that, in each array, the said discrete conductive strips of each pair which have a said relatively large centre-to-centre spacing are connected to the respective strips of a pair in the other array which have a said relatively small centre-to-centre spacing, characterised in that each array includes a plurality of further electrically conductive strips which are parallel to the said discrete conductive strips of that array, in that said further strips are situated between the respective discrete conductive strips forming substantially every pair having a said relatively large centre-to-centre spacing, and in that all said further electrically conductive strips in both said arrays are electrically interconnected.

Claim 5

A device as claimed in claims 1 or 3 characterised in that all of the said relatively large centre-to-centre spacings are substantially equal to each other, as are all of the said relatively small centre-to-centre spacings.

Claim 6

A device as claimed in claims 1 or 3 characterised in that said relatively large centre-to-centre spacings have a periodicity of λ o along each array, where λ o is the acoustic surface wavelength at the mid-band frequency f o of the device.

Claim 7

A device as claimed in claims 1 or 3 characterised in that in each said array said discrete conductive strips and said further strips are substantially uniformly spaced along the array.

Claim 9

A device as claimed in claims 1 or 3 characterised in that an electrical interconnection of said further electrically conductive strips comprises a common electrical conductor in the form of respective strip-like portions disposed along the outer edge of a corresponding array and parallel to the acoustic surface wave propagation direction along that array, and a linking electrically conducting strip-like portion disposed across an end of said electrical coupling means and arranged so that substantially no undesired surface acoustic wave signal is transduced thereby in the propagation direction along either array.