A phased array antenna comprises an array of reflective cells, each cell being defined by a wall positioned within the array the wall arranged to define a waveguide, and having a moveable reflector positioned within the wall. Each reflector is arranged such that it is not in electrical contact with its respective wall and such that, in use it can be moved to tune the antenna. A feed and subreflector are positioned within the array and arranged to transmit and/or receive electromagnetic signals to and/or from the array.