A feed network, steering apparatus and system for a steerable antenna array are described. The feed network includes a waveguide assembly including first and second radial transverse electromagnetic (TEM) waveguides, and first and second variable phase shifters positioned in the respective TEM waveguides. The variable phase shifters cause additional progressive electrical phase shifts in respective rings of radiating elements, directly proportional to the angular position of the radiating elements in the ring, from 0 to a controllable integer multiple of 2π radians. The feed network includes first and second phase-mode feed probes coupled to the respective radial TEM waveguides, which provide respective phase-mode feed ports. When the feed network is coupled to the antenna array, two consecutive-order phase modes are provided at the phase-mode feed ports. The orders of the phase modes are selectable using a phase shift control signal controlling the integer multiple of the variable phase shifters.