Beamforming Analysis of Dual Beam Antenna Array Using Theory of Characteristic Modes

This paper presents a novel and insightful approach to beamforming a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> antenna array using the theory of characteristic modes. The array comprises four rectangular patch antenna elements designed on an FR-4 substrate resonating at 2.4 GHz. The characteristic mode analysis (CMA) presented a fascinating physical insight into the surface current directions and the radiation characteristics of the array structure. The excitation of a specific characteristic mode led to the design of a dual-beam antenna array. After feed excitation, characteristic mode analysis (CMA) was employed to understand multi-beam pattern reconfigurability in the multi-port structure. The information of distinct and orthogonal modal characteristic fields guides the beamforming of multibeam arrays. Modal characteristic fields of specific modes were identified using a modal weighting coefficient that may combine upon port phase change for beamforming at a certain scan angle. The potential of multi-dimensional coverage of a multibeam array is presented by selecting the different phase combinations of feeding ports. The paper discusses the strengths and limitations of beam scanning due to the combination of modes. This physical insight is beneficial for future pattern reconfigurable antenna array design procedures. Measurements on a realized prototype are in a good agreement with simulations, proving the proposed concept.