Embodiments herein include a method for obtaining a calibration parameter for an antenna array. The antenna array comprises a first and a second radio module with respective associated antennas, wherein both radio modules comprise a main transmitter and a connected calibration receiver or both radio modules comprise a main receiver and a connected calibration transmitter. The method comprises: injecting a first calibration signal in the first radio module and measuring a first response to the first calibration in the first radio module. This injecting and measuring is repeated for all combinations of the first and second radio modules. Finally, a numerical value is calculated using the responses; a calibration parameter is calculated based on the calculated numerical value. Embodiments herein also include a corresponding antenna array, computer program and computer program product.