A method of determining a 3-dimensional direction-of-arrival of radiation impingent on a sensor having exactly 4 or exactly 5 receiving antennas each being adapted to sense the radiation and output a corresponding signal, the method comprising: positioning the antennas so that: at least 3 of the antennas are first receiving antennas which define-corners of a parallelogram having two first and two second parallel sides, one or more of the receiving antennas is/are second receiving antenna(s), each second antenna forming a pair of antennas with one of the first antennas, where the second antenna of each pair is positioned more than 2% of a smallest distance between two first receiving antennas away from all axes extending through: any two of the four corners of the parallelogram; any corner of the parallelogram and a centre point of any of the four sides of the parallelogram; and the centre point of any of the sides of the parallelogram and the centre point of any other side of the parallelogram and determining the 3-dimensional direction-of-arrival from at least: a phase difference between a first pair of the first receiving antennas positioned on one of the first parallel sides and a distance between the antennas of the first pair of antennas, a phase difference between a second pair of the first receiving antennas positioned on one of the second parallel sides and a distance between the antennas of the second pair of antennas, and a phase difference between a third pair of antennas, being a pair of antennas comprising a second receiving antenna and a first antenna, and a distance between the antennas of the third pair of antennas. positioning the antennas so that: at least 3 of the antennas are first receiving antennas which define-corners of a parallelogram having two first and two second parallel sides, one or more of the receiving antennas is/are second receiving antenna(s), each second antenna forming a pair of antennas with one of the first antennas, where the second antenna of each pair is positioned more than 2% of a smallest distance between two first receiving antennas away from all axes extending through: any two of the four corners of the parallelogram; any corner of the parallelogram and a centre point of any of the four sides of the parallelogram; and the centre point of any of the sides of the parallelogram and the centre point of any other side of the parallelogram and at least 3 of the antennas are first receiving antennas which define-corners of a parallelogram having two first and two second parallel sides, one or more of the receiving antennas is/are second receiving antenna(s), each second antenna forming a pair of antennas with one of the first antennas, where the second antenna of each pair is positioned more than 2% of a smallest distance between two first receiving antennas away from all axes extending through: any two of the four corners of the parallelogram; any corner of the parallelogram and a centre point of any of the four sides of the parallelogram; and the centre point of any of the sides of the parallelogram and the centre point of any other side of the parallelogram and determining the 3-dimensional direction-of-arrival from at least: a phase difference between a first pair of the first receiving antennas positioned on one of the first parallel sides and a distance between the antennas of the first pair of antennas, a phase difference between a second pair of the first receiving antennas positioned on one of the second parallel sides and a distance between the antennas of the second pair of antennas, and a phase difference between a third pair of antennas, being a pair of antennas comprising a second receiving antenna and a first antenna, and a distance between the antennas of the third pair of antennas. a phase difference between a first pair of the first receiving antennas positioned on one of the first parallel sides and a distance between the antennas of the first pair of antennas, a phase difference between a second pair of the first receiving antennas positioned on one of the second parallel sides and a distance between the antennas of the second pair of antennas, and a phase difference between a third pair of antennas, being a pair of antennas comprising a second receiving antenna and a first antenna, and a distance between the antennas of the third pair of antennas.