Abstract: The present invention relates to a device at an antenna for eliminating grid lobes in the radar cross section of the antenna.The invention displaces the grid lobes to a frequency range outside the working frequency of the antenna by inserting rows of dummy elements (r.sub.3, r.sub.4, r.sub.5) between rows of ordinary antenna elements (r.sub.1, r.sub.2) in the antenna (11). The dummy elements will behave like the ordinary antenna elements (15) as regards the rescattering when the dummy elements (17) are irradiated with signals from outside. Furthermore, the dummy elements (17) are not fed by a feeding network (16a, 16b) with microwave signals as is the case with the ordinary antenna elements (15). The dummy elements (17) are arranged in the rows of dummy elements (r.sub.3, r.sub.4, r.sub.5) so that the distances in X-direction and in Y-direction (a.sub.4, a.sub.5, a.sub.6, a.sub.7, a.sub.