An antenna array assembly comprises a ground plate, a linear array of patch radiator elements disposed in a spaced parallel relationship with a first face of the ground plate and a first and second elongate passive radiator each comprising a plurality of conductive parts electrically isolated from the ground plate. The first and second elongate passive radiators are disposed symmetrically on either side of the linear array and parallel to a centre line of the linear array, on the same side of the ground plate as the linear array. At least some of the conductive parts of a respective elongate passive radiator are disposed in an arrangement having parallel ridges and grooves, in which, in a cross section in a plane parallel to the first face of the ground plate, the ridges extend towards the linear array and the grooves extend away from the linear array.