There is provided mechanisms for signal transmission diversity at an antenna array of a radio transceiver device. The antenna array has two physical antenna ports. A method is performed by the radio transceiver device. The method comprises creating two virtual antenna ports for each of the two physical antenna ports, resulting in four virtual antenna ports. The method comprises transmitting the signal from the four virtual antenna ports towards another radio transceiver device over four different radio propagation channels, one radio propagation channel per virtual antenna port.