A Multiple-Input Multiple-Output, MIMO, omnidirectional antenna comprising three or more column sets, where the three or more column sets are arranged in a centrosymmetric arrangement about a centre point of the antenna; each column set comprising two or more antenna columns (302A-F) and each of the antenna columns (302A-F) comprising a plurality of radiators mounted thereon; whereby, each antenna column (302A-F) comprises no more than two antenna ports for receiving the signals to be transmitted, and, each of the antenna columns (302A-F) is arranged to be axisymmetric about a radially-directed axis which extends between the centre point of the antenna and a transverse cross-sectional midpoint on the antenna column (302A-F); wherein the arrangement of the column sets is such that, each radiation pattern established by each of the three or more column sets is centrosymmetric about the centre point of the antenna, and, is axisymmetric about the radially-directed axis, the Multiple-Input Multiple-Output antenna comprising six antenna columns (302A-F) arranged in a hexagonal arrangement; each of the six antenna columns (302A-F) being substantially rectangular in shape such as to comprise side edges (310,312), a top edge and a bottom edge whereby the side edges (310,312) are longer than the top and bottom edges; each of the six antenna columns (302A-F) being positioned adjacent to two of the remaining antenna columns (302A-F) along its side edges (310,312), such that the six antenna columns (302A-F) are arranged to have a substantially hexagonal transverse cross-section; wherein, the Multiple-Input Multiple-Output omnidirectional antenna is a 4×4 Multiple-Input Multiple-Output omnidirectional antenna comprising four antenna ports for receiving four signals to be transmitted; two of the four ports being connected to three of the six antenna columns (302A-F) and the other two ports being connected to the other three antenna columns (302A-F); whereby, the antenna columns (302A-F) are configured such that an antenna column (302A-F) connected to two of the antenna ports is situated intermediate two adjacent antenna columns (302A-F) connected to the other two ports. each column set comprising two or more antenna columns (302A-F) and each of the antenna columns (302A-F) comprising a plurality of radiators mounted thereon; whereby, each antenna column (302A-F) comprises no more than two antenna ports for receiving the signals to be transmitted, and, each of the antenna columns (302A-F) is arranged to be axisymmetric about a radially-directed axis which extends between the centre point of the antenna and a transverse cross-sectional midpoint on the antenna column (302A-F); wherein the arrangement of the column sets is such that, each radiation pattern established by each of the three or more column sets is centrosymmetric about the centre point of the antenna, and, is axisymmetric about the radially-directed axis, the Multiple-Input Multiple-Output antenna comprising six antenna columns (302A-F) arranged in a hexagonal arrangement; each of the six antenna columns (302A-F) being substantially rectangular in shape such as to comprise side edges (310,312), a top edge and a bottom edge whereby the side edges (310,312) are longer than the top and bottom edges; each of the six antenna columns (302A-F) being positioned adjacent to two of the remaining antenna columns (302A-F) along its side edges (310,312), such that the six antenna columns (302A-F) are arranged to have a substantially hexagonal transverse cross-section; wherein, the Multiple-Input Multiple-Output omnidirectional antenna is a 4×4 Multiple-Input Multiple-Output omnidirectional antenna comprising four antenna ports for receiving four signals to be transmitted; two of the four ports being connected to three of the six antenna columns (302A-F) and the other two ports being connected to the other three antenna columns (302A-F); whereby, the antenna columns (302A-F) are configured such that an antenna column (302A-F) connected to two of the antenna ports is situated intermediate two adjacent antenna columns (302A-F) connected to the other two ports.