An antenna array assembly, comprising: a plurality of ground plates (2a, 2b); at least a first and second antenna element (3a, 3b), each antenna element comprising at least one patch radiator element disposed in a substantially parallel relationship to a respective ground plate, and each patch radiator element being disposed in the same orientation; and an isolator bar (lb) disposed between the respective ground plates of the first and second antenna elements, the isolator bar being elongate having a cross-section comprising a T shape, the cross-section being across a long axis so that the isolator bar is longer in a direction normal to the cross-section than in a direction across the cross-section, the isolator bar (lb) comprising: a support bar in contact with the ground plates of the first and second antenna elements, the support bar forming the stem of the T shape; and a substantially planar cross piece forming the top of the T shape and being disposed in a parallel relationship with the planes of the ground plates of the first and second antenna elements on the same side of the ground plates as the patch radiator elements, wherein the cross piece of the isolator bar has a width in the cross-section of at least a quarter of a wavelength at an operating frequency of the antenna array assembly, whereby to provide radio frequency isolation between the first and second antenna elements. a plurality of ground plates (2a, 2b); at least a first and second antenna element (3a, 3b), each antenna element comprising at least one patch radiator element disposed in a substantially parallel relationship to a respective ground plate, and each patch radiator element being disposed in the same orientation; and an isolator bar (lb) disposed between the respective ground plates of the first and second antenna elements, the isolator bar being elongate having a cross-section comprising a T shape, the cross-section being across a long axis so that the isolator bar is longer in a direction normal to the cross-section than in a direction across the cross-section, the isolator bar (lb) comprising: a support bar in contact with the ground plates of the first and second antenna elements, the support bar forming the stem of the T shape; and a substantially planar cross piece forming the top of the T shape and being disposed in a parallel relationship with the planes of the ground plates of the first and second antenna elements on the same side of the ground plates as the patch radiator elements, wherein the cross piece of the isolator bar has a width in the cross-section of at least a quarter of a wavelength at an operating frequency of the antenna array assembly, whereby to provide radio frequency isolation between the first and second antenna elements. a support bar in contact with the ground plates of the first and second antenna elements, the support bar forming the stem of the T shape; and a substantially planar cross piece forming the top of the T shape and being disposed in a parallel relationship with the planes of the ground plates of the first and second antenna elements on the same side of the ground plates as the patch radiator elements, wherein the cross piece of the isolator bar has a width in the cross-section of at least a quarter of a wavelength at an operating frequency of the antenna array assembly, whereby to provide radio frequency isolation between the first and second antenna elements.