An aperture coupled patch antenna element comprises a ground plate having first and second opposite sides and an aperture passing through the ground plate from the first side to the second side. The aperture comprises a slot, the slot having an elongate cross-section in the plane of the first side of the ground plate, the cross-section having substantially parallel sides extending along the length of the cross-section, and the slot having a width which is the distance between the parallel sides of the cross-section of the slot. The antenna element also comprises a first transmission line comprising a first elongate conductor disposed on the first side of the ground plate in a substantially parallel relationship with the first side of the ground plate, and a patch radiator disposed on the second side of the ground plate in a substantially parallel relationship with the second side of the ground plate, the first transmission line being arranged to cross the slot, and the patch radiator is arranged to overlie the slot. The thickness of the ground plate at the slot is greater than the width of the slot. Fig: 1
