A method of determining sign of a calibration compensation for use in an antenna system, the antenna system comprising a first individually calibrated subarray and a second individually calibrated subarray, the method being performed in a control device and comprising: - selecting a set of antenna elements comprising two neighboring antenna elements of the first subarray and two neighboring antenna elements of the second subarray, - measuring: - in a selected antenna element of the first subarray a first received signal Y 31 as transmitted from the other selected antenna element of the first subarray and a second received signal Y 34 as transmitted from one of the neighboring antenna elements of the second subarray, and - in a selected antenna element of the second subarray a third received signal Y 24 as transmitted from the other selected antenna element of the second subarray and a fourth received signal Y 21 as transmitted from one of the neighboring antenna elements of the first subarray, - calculating for the first calibrated subarray a downlink compensation value Δ t a and an uplink compensation value Δr a based on measurement values obtained from the measuring, each compensation value Δ t a, Δ r a having a positive and a negative solution, - determining a first compensation value estimate, k t, for downlink compensation and a second compensation value estimate, k r, for uplink compensation, by using equations: k t = C 2 ⋅ Y 31 C 1 ⋅ Y 34 k r = C 2 ⋅ Y 31 C 1 ⋅ Y 21, wherein C 1 is the mutual coupling between the selected two neighboring elements of the same subarray (2a, 2b) and C 2 is the mutual coupling between a selected antenna element of the first subarray and a neighboring antenna element of the second subarray, obtaining the mutual couplings C 1, C 2 by s-parameter measurements, wherein the s-parameter describes an input-output relationship between ports of the antenna system or by software simulations and - determining the sign of the downlink compensation value Δ t a and the sign of the uplink compensation value Δ r a based on distance between the first compensation value estimate k t and the downlink compensation value, Δ t a, and the distance between the second compensation value estimate, k r, and the uplink compensation value Δ r a. - selecting a set of antenna elements comprising two neighboring antenna elements of the first subarray and two neighboring antenna elements of the second subarray, - measuring: - in a selected antenna element of the first subarray a first received signal Y 31 as transmitted from the other selected antenna element of the first subarray and a second received signal Y 34 as transmitted from one of the neighboring antenna elements of the second subarray, and - in a selected antenna element of the first subarray a first received signal Y 31 as transmitted from the other selected antenna element of the first subarray and a second received signal Y 34 as transmitted from one of the neighboring antenna elements of the second subarray, and - in a selected antenna element of the second subarray a third received signal Y 24 as transmitted from the other selected antenna element of the second subarray and a fourth received signal Y 21 as transmitted from one of the neighboring antenna elements of the first subarray, - calculating for the first calibrated subarray a downlink compensation value Δ t a and an uplink compensation value Δr a based on measurement values obtained from the measuring, each compensation value Δ t a, Δ r a having a positive and a negative solution, - determining a first compensation value estimate, k t, for downlink compensation and a second compensation value estimate, k r, for uplink compensation, by using equations: k t = C 2 ⋅ Y 31 C 1 ⋅ Y 34 k r = C 2 ⋅ Y 31 C 1 ⋅ Y 21, wherein C 1 is the mutual coupling between the selected two neighboring elements of the same subarray (2a, 2b) and C 2 is the mutual coupling between a selected antenna element of the first subarray and a neighboring antenna element of the second subarray, obtaining the mutual couplings C 1, C 2 by s-parameter measurements, wherein the s-parameter describes an input-output relationship between ports of the antenna system or by software simulations and - determining the sign of the downlink compensation value Δ t a and the sign of the uplink compensation value Δ r a based on distance between the first compensation value estimate k t and the downlink compensation value, Δ t a, and the distance between the second compensation value estimate, k r, and the uplink compensation value Δ r a.