An adaptable dual-gridded reflector geometry for optimum cross-polar performance

A dual-gridded reflector antenna consists of two separate polarized (gridded) reflectors gridded in orthogonal directions (i.e. vertical and horizontal). Each of these two gridded reflectors is illuminated by a single feed (or a feed array) which is polarized along the direction of the grid. The focus for each of the reflectors is chosen to be separated enough for the given cross-polar requirement. The cross-polarization currents on a reflector from its feed are attenuated due to the grids. This component can be called the ´right reflector´ cross-polarization. The cross-polarization currents from the feed induced on the orthogonally polarized reflector are not attenuated since the grids are also along the cross-polar direction. However, the feed is displaced from the focus of the orthogonally polarized reflector and so the cross-polar radiation is usually scanned away from the coverage area. This component, which is dependent on the geometry of the two reflectors, is called the ´wrong reflector´ cross-polarization. The ´right reflector´ cross-polarization depends on the grid parameters and so is easily controlled. However, the ´wrong reflector´ cross-polarization depends on the feed separation and so is always traded against mechanical complexity. This paper relates to the ´wrong reflector´ cross-polarization.