The invention relates to an antenna. The antenna comprises a feed line having first and second ends on opposite sides of the feed line, wherein a transmission axis is defined as the axis extending between the first and second ends of the feed line. Further, the antenna comprises a plurality of antenna elements arranged along the feed line, protruding from the transmission axis. The antenna also comprises a first port at the first end of the feed line, wherein, at a first part of the antenna, the feed line, from the first port towards a reference point along the transmission axis, comprises antenna elements of gradually increasing length, configured to radiate in a first direction along the transmission axis from the reference point towards the first port during excitation in the first port. Yet further, the antenna comprises a second port at the second end of the feed line, wherein, at a second part of the antenna, the feed line, from the second port towards the reference point along the transmission axis, comprises antenna elements of gradually increasing length, configured to radiate in a second direction along the transmission axis from the reference point towards the second port during excitation in the second port.