This disclosure provides a microwave radio transmitter apparatus comprising an antenna arrangement and a precoder module connected to the antenna arrangement. The precoder module comprises an estimation module. The precoder module is configured to receive a number N of signals s1, . . . , sN and to generate N phase-adjusted transmit signals TX1, . . . , TXN. The antenna arrangement comprises N antenna elements ai, i=1, 2, . . . , N. Each antenna element ai is configured to obtain a respective phase-adjusted transmit signal TXi from the pre-coder and to transmit the respective phase-adjusted transmit signal TXi. The precoder module is configured to obtain an observation receive signal RX, the observation receive signal comprising signals transmitted from the N antenna elements. The estimation module is configured to estimate for each antenna element ai a phase difference between the corresponding transmit signal TXi and the observation receive signal RX. The precoder module is configured to adjust each transmit signal based on the estimated phase difference.