The disclosed apparatus may include (1) an antenna assembly defining an upper cavity with an aperture, the antenna assembly further defining a lower cavity coupled to the upper cavity via a channel along a linear edge of the antenna assembly, where the antenna assembly may include a reflective element within the lower cavity having a concave parabolic contour, and (2) an array assembly positioned in the aperture and including an array of passive elements. The reflective element may transform a divergent radio frequency (RF) beam directed toward the concave parabolic contour within the lower cavity into a collimated RF beam propagating within the lower cavity and into the upper cavity via the channel, and the array of passive elements may radiate a transmitted RF beam from the aperture in response to the collimated RF beam in the upper cavity. Various other apparatuses, methods, and systems are also disclosed.