An Accurate Near-Field Focusing of Array Antenna Based on Near-Field Active Element Pattern and Infinitesimal Dipole Modeling

There are mainly three issues for Near-Field Focusing (NFF) using an antenna array. First, it is required to know the distribution of the near electric field in 3D space for each antenna element. In general, a huge amount of data is required to express the near-field for each antenna element in a 3D space with high resolution. Second, in the trade-off relationship between efficiency and accuracy for NFF, we require to solve the optimization problem in which energy can be concentrated to the focal point. Solving optimization problems with near-field represented by huge amounts of data is very inefficient. Third, accurate NFF must be performed by reflecting the mutual coupling phenomenon between antennas. In this paper, there are three key ideas to overcome the issues in the NFF by improving both accuracy and efficiency. The first is the extraction of the infinitesimal dipole model (IDM) using the active element pattern. This makes it possible to obtain a mathematical model of the antenna that perfectly reflects the mutual coupling effect. The second is the acquisition of near-field data to an adaptive resolution grid with appropriate resolution using the extracted IDM. This re-radiated near-field data has both accuracy and efficiency by maintaining high resolution only for a focal point. The third is an efficient optimization method for a desired focal area with an arbitrary elliptical shape using convex optimization. Through simulations for the verification, 4 types of grids with various resolutions are used to the same NFF problem. The computational time of the proposed method in optimization for the NFF could be reduced to 8% with a similar focal shift compared to a type of the finest resolution. In addition, the accuracy of the electromagnetic analysis of the proposed method was verified through comparative verification with the MoM results.