1. A method for obtaining at least one calibration parameter for an antenna array, the antenna array comprising a first and a second radio module, a first antenna and a second antenna respectively connected to the first and second radio modules, wherein the first and second radio modules each comprises a main transmitter and a selectively connectable calibration receiver or the first and second radio modules each comprises a main receiver and a selectively connectable calibration transmitter, the method comprising: injecting a first calibration signal in the first radio module and measuring a first response to the first calibration signal in the first radio module; injecting a second calibration signal in the first radio module that passes over mutual coupling of the antennas to the second radio module, and measuring a second response to the second calibration signal in the second radio module; injecting a third calibration signal in the second radio module and measuring a third response to the third calibration signal in the second radio module; injecting a fourth calibration signal in the second radio module that passes over mutual coupling of the antennas to the first radio module, and measuring a fourth response to the fourth calibration signal in the first radio module; calculating at least one numerical value using the first, second, third and fourth responses; and calculating at least one calibration parameter based on the calculated numerical value.