Considered in this article synthetic method of a one-side reduction of the side lobes level of the total radiation pattern of the antenna system is one of the options to protect onboard weather radars operating in the modes of airspace overview for searching for dangerous weather formations and/or point and group air targets (manned planes and helicopters or drones) from interference signals coming from the underlying surface. The method is adaptive: interference signals from the ground are subjected to spatial rejection in the purpose angular range, determined by the size of the range of the current overviewing area. Unfortunately, the practical implementation of the method is usually associated with many destabilizing factors, for example, errors in the amplitude-phase distribution over the antenna array. In this paper special attention is paid to the analysis of the influence of the such destabilizing factors on the effectiveness of the synthetic method, as well as on the characteristics of the direction and direction-finding of antenna of the onboard radar.