A feed network for a steerable antenna array, the feed network comprising: a waveguide assembly including: a first radial transverse electromagnetic,TEM, waveguide and a second radial TEM waveguide, the first radial TEM waveguide including a first plurality of radiating element probes for coupling to a first ring of radiating elements of the antenna array and the second radial TEM waveguide including a second plurality of radiating element probes for coupling to a second ring of radiating elements of the antenna array; a first variable phase shifter positioned in the first radial TEM waveguide, the first variable phase shifter being configured to cause additional progressive electrical phase shifts in the first ring of radiating elements, directly proportional to angular position of the radiating elements in the first ring, from 0 to an integer multiple of 2π radians, the integer multiple being controllable; and a second variable phase shifter positioned in the second radial TEM waveguide, the second variable phase shifter being configured to cause additional progressive electrical phase shifts in the second ring of radiating elements, directly proportional to angular position of the radiating elements in the second ring, from 0 to an integer multiple of 2π radians, the integer multiple being controllable; and first and second phase-mode feed probes (108a, 108b) coupled to the first and second radial TEM waveguides (106a, 106b), respectively, the phase-mode feed probes providing respective phase-mode feed ports; wherein, 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 being selectable in accordance with at least one phase shift control signal controlling the integer multiple of the first and second variable phase shifters. a waveguide assembly including: a first radial transverse electromagnetic,TEM, waveguide and a second radial TEM waveguide, the first radial TEM waveguide including a first plurality of radiating element probes for coupling to a first ring of radiating elements of the antenna array and the second radial TEM waveguide including a second plurality of radiating element probes for coupling to a second ring of radiating elements of the antenna array; a first variable phase shifter positioned in the first radial TEM waveguide, the first variable phase shifter being configured to cause additional progressive electrical phase shifts in the first ring of radiating elements, directly proportional to angular position of the radiating elements in the first ring, from 0 to an integer multiple of 2π radians, the integer multiple being controllable; and a second variable phase shifter positioned in the second radial TEM waveguide, the second variable phase shifter being configured to cause additional progressive electrical phase shifts in the second ring of radiating elements, directly proportional to angular position of the radiating elements in the second ring, from 0 to an integer multiple of 2π radians, the integer multiple being controllable; and a first radial transverse electromagnetic,TEM, waveguide and a second radial TEM waveguide, the first radial TEM waveguide including a first plurality of radiating element probes for coupling to a first ring of radiating elements of the antenna array and the second radial TEM waveguide including a second plurality of radiating element probes for coupling to a second ring of radiating elements of the antenna array; a first variable phase shifter positioned in the first radial TEM waveguide, the first variable phase shifter being configured to cause additional progressive electrical phase shifts in the first ring of radiating elements, directly proportional to angular position of the radiating elements in the first ring, from 0 to an integer multiple of 2π radians, the integer multiple being controllable; and a second variable phase shifter positioned in the second radial TEM waveguide, the second variable phase shifter being configured to cause additional progressive electrical phase shifts in the second ring of radiating elements, directly proportional to angular position of the radiating elements in the second ring, from 0 to an integer multiple of 2π radians, the integer multiple being controllable; and first and second phase-mode feed probes (108a, 108b) coupled to the first and second radial TEM waveguides (106a, 106b), respectively, the phase-mode feed probes providing respective phase-mode feed ports; wherein, 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 being selectable in accordance with at least one phase shift control signal controlling the integer multiple of the first and second variable phase shifters.