This paper presents a method to use a single planar antenna array with a conserved number of elements to generate multiple LG modes simultaneously, so that OAM-based spatial multiplexing can be realized. The method considers generating modes of various l and p values to fully take advantage of the spatial diversity offered by both the azimuthal domain and the radial domain. At the same time of ensuring the multiplexed signal can be resolved over a finite receive aperture, the sidelobe radiation beyond the aperture is controlled to reduce the possible interference to other users in the surrounding environment.