Beam-Steering Array Antenna Fed by an Azimuthally Inhomogeneous Radial Waveguide

Achieving high-efficiency beam-steerable low-profile mm-wave array antennas has become particularly relevant for the advancement of modern communication systems. A completely novel passive approach to steer the directive beam of large low-profile circular arrays is proposed here. This method is enabled when an unequally spaced array is fed by an inhomogeneous radial waveguide. When array spacing and waveguide permittivity satisfy an optimal azimuthal distribution, a simple in-plane rotation of one antenna part provides the desired elevation scanning feature. The analytical design expressions are derived, and the theoretical performance is assessed, confirming the suitability of the proposed beam-steering method. A first practical implementation is conceived as a demonstrator, consisting of a slot array fed by an all-metal radial waveguide filled with an inhomogeneous bed of nails (BoNs). Experimental validation of the constructed prototype confirms the beam-steering property with a peak gain above 30 dBi and a maximum scan angle of 20° at 30 GHz. The proposed approach allows further improvement of the field of view by adopting a more versatile waveguide permittivity synthesis.