The invention discloses an antenna assembly comprising one or more sensors, possibly a fish-eye camera which produces images of the sky above the antenna, said images being processed to identify open sky and occulted sky areas, said identification being used to generate an antenna gain pattern shape wherein null zones are placed on the occulted sky areas, so as to eliminate the GNSS signals which are affected by multipath reflection. The antenna assembly of the invention may be used with any GNSS receiver of the prior art. No specific data on the location of the receiver or its orientation is needed to perform the method of the invention, while in some embodiments, it may be useful to send some information on the number of satellites in view in the open sky.