The invention discloses an antenna device (500, 600, 700) for a radio base station in a cellular telephony system, which comprises a first and a second input connection for a first (D1) and a second (D2) data stream, and a first (510, 610, 710) and a second (511, 611, 711) polarization former, one for each of said data streams. The device also comprises a first (530, 630, 730) and a second (532, 632, 732) antenna of respective first and second polarizations, and one amplifier each. The device also comprises a first (515, 615, 715) and a second (516, 616, 716) combiner, so that the outputs from the polarization formers may be combined as input to each of the first and second antennas.