A power combiner/splitter for multiple input multiple output, "MIMO", applications, the power combiner/splitter comprising: a metallisation stack formed on a surface, the metallisation stack comprising a plurality of layers (204, 206, 208, 210) including patterned metal features, the patterned metal features forming: a first branched arrangement forming a first combiner/splitter, the first branched arrangement comprising: a first port located at one end of the first branched arrangement; a plurality of further ports (32, 34, 36, 38); a plurality of bifurcated branches extending between the first port of the first branched arrangement and the plurality of further ports of the first branched arrangement for dividing/combining a signal passing through the first branched arrangement between the first port and the plurality of further ports of the first branched arrangement; and a second branched arrangement forming a second combiner/splitter, the second branched arrangement comprising: a first port located at one end of the second branched arrangement; a plurality of further ports (132, 134, 136, 138); a plurality of bifurcated branches extending between the first port of the second branched arrangement and the plurality of further ports of the first branched arrangement for dividing/combining a signal passing through the second branched arrangement between the first port and the plurality of further ports of the second branched arrangement; wherein the metallisation stack further comprises a common ground plane shared by the first and second branched arrangements, wherein the first branched arrangement and the second branched arrangement are located in a common area of the metallisation stack such that at least some of the patterned metal features forming the first branched arrangement overlie at least some of the patterned metal features forming the second branched arrangement, characterized in that the patterned metal features forming at least some of the branches of the first branched arrangement are formed in a same layer of the metallisation stack as the patterned metal features forming at least some of the branches of the second branched arrangement. a first branched arrangement forming a first combiner/splitter, the first branched arrangement comprising: a first port located at one end of the first branched arrangement; a plurality of further ports (32, 34, 36, 38); a plurality of bifurcated branches extending between the first port of the first branched arrangement and the plurality of further ports of the first branched arrangement for dividing/combining a signal passing through the first branched arrangement between the first port and the plurality of further ports of the first branched arrangement; and a first port located at one end of the first branched arrangement; a plurality of further ports (32, 34, 36, 38); a plurality of bifurcated branches extending between the first port of the first branched arrangement and the plurality of further ports of the first branched arrangement for dividing/combining a signal passing through the first branched arrangement between the first port and the plurality of further ports of the first branched arrangement; and a second branched arrangement forming a second combiner/splitter, the second branched arrangement comprising: a first port located at one end of the second branched arrangement; a plurality of further ports (132, 134, 136, 138); a plurality of bifurcated branches extending between the first port of the second branched arrangement and the plurality of further ports of the first branched arrangement for dividing/combining a signal passing through the second branched arrangement between the first port and the plurality of further ports of the second branched arrangement; a first port located at one end of the second branched arrangement; a plurality of further ports (132, 134, 136, 138); a plurality of bifurcated branches extending between the first port of the second branched arrangement and the plurality of further ports of the first branched arrangement for dividing/combining a signal passing through the second branched arrangement between the first port and the plurality of further ports of the second branched arrangement; wherein the metallisation stack further comprises a common ground plane shared by the first and second branched arrangements, wherein the first branched arrangement and the second branched arrangement are located in a common area of the metallisation stack such that at least some of the patterned metal features forming the first branched arrangement overlie at least some of the patterned metal features forming the second branched arrangement, characterized in that the patterned metal features forming at least some of the branches of the first branched arrangement are formed in a same layer of the metallisation stack as the patterned metal features forming at least some of the branches of the second branched arrangement.