A four port antenna decoupling network having: first (port 1) and second (port 2) ports coupled, in use, either directly to antenna elements or indirectly to antenna elements; third (port 3) and fourth (port 4) ports coupled, in use, either directly or indirectly to radio transmitting and/or receiving apparatus; characterized by the first (port 1) and second (port 2) ports each having first connection points and second connection points, the first connection points of the first and second ports being directly connected to each other, the second connection points of the first and second ports being connected to each other via at least a pair of positive capacitors 2 − 1 C, 2 − 1 C, the pair of positive capacitors having a common junction point between them; the third port (port 3) having first and second connection points, the first connection point of the third port being capacitively coupled to a first one (( ( ( 2 − 1) C) of said pair of positive capacitors 2 − 1 C, 2 − 1 C with a first negative capacitor − c 2 and the second connection point of the third port (port 3) being directly coupled to a second one 2 − 1 C of said pair of positive capacitors ( ( 2 − 1) C, 2 − 1 C); the fourth port (port 4) having first and second connection points, the first connection point of the fourth port (port 4) being directly coupled to the first connection points of the first (port 1) and second (port 2) ports, and the second connection point of the fourth port being coupled to the first connection point of the fourth port via two additional positive capacitors C, 2 − 1 C having a common junction point between them; the common junction point between the pair of positive capacitors 2 − 1 C, 2 − 1 C being connected to the common junction point between the two additional positive capacitors C, 2 − 1 C via a negative capacitor − 2 − 1 C. first (port 1) and second (port 2) ports coupled, in use, either directly to antenna elements or indirectly to antenna elements; third (port 3) and fourth (port 4) ports coupled, in use, either directly or indirectly to radio transmitting and/or receiving apparatus; characterized by the first (port 1) and second (port 2) ports each having first connection points and second connection points, the first connection points of the first and second ports being directly connected to each other, the second connection points of the first and second ports being connected to each other via at least a pair of positive capacitors 2 − 1 C, 2 − 1 C, the pair of positive capacitors having a common junction point between them; the third port (port 3) having first and second connection points, the first connection point of the third port being capacitively coupled to a first one (( ( ( 2 − 1) C) of said pair of positive capacitors 2 − 1 C, 2 − 1 C with a first negative capacitor − c 2 and the second connection point of the third port (port 3) being directly coupled to a second one 2 − 1 C of said pair of positive capacitors ( ( 2 − 1) C, 2 − 1 C); the fourth port (port 4) having first and second connection points, the first connection point of the fourth port (port 4) being directly coupled to the first connection points of the first (port 1) and second (port 2) ports, and the second connection point of the fourth port being coupled to the first connection point of the fourth port via two additional positive capacitors C, 2 − 1 C having a common junction point between them; the common junction point between the pair of positive capacitors 2 − 1 C, 2 − 1 C being connected to the common junction point between the two additional positive capacitors C, 2 − 1 C via a negative capacitor − 2 − 1 C.