Patent ID: 8228135

Claim:
A band combining filter for passing signals in a communications band, the band combining filter comprising; a plurality of cascaded directional filters, each directional filter having at least two inputs and at least two outputs, the nth directional filter being arranged such that the output signals O 1 and O 2 from the first and second outputs are related to the input signals I 1 , I 2 to the first and second inputs by the relation ( O 1 O 2 ) = ( R n ⁢ ⁢ 1 T n ⁢ ⁢ 2 T n ⁢ ⁢ 1 R n ⁢ ⁢ 2 ) ⁢ ( I 1 I 2 ) with R and T being reflection and transmission functions respectively; the directional filters being connected in a cascade with the first and second inputs of the nth directional filter being connected to the first and second outputs of the (n−1) th directional filter respectively in the cascade; characterised in that at least one of the reflection functions R n overlaps with the corresponding reflection function R n−1 within the communication band but is different thereto.