Ka‐band multi‐focus and pattern manipulation in near‐field based on three‐dimensional printed transmit‐array antenna

Abstract

A simple method to achieve multi‐focus and pattern manipulation in antenna near field (NF) is proposed in this study, whose effectiveness is then validated by measurements based on different transmit‐array antennas. The radiating aperture is divided into several regions and each region corresponds to one assigned focal point, thus achieving multi‐focusing performance. Then, the superposition principle is employed and constrains the multiple foci into a certain area to get a contoured pattern. Three examples are investigated. Ant‐A presents four balanced focal spots simultaneously, while Ant‐B presents two unbalanced foci. A square flat‐top field pattern is obtained for Ant‐C. Three‐dimensional printing technology is employed to fabricate these lenses, resulting in a low cost and light weight. Measured results coincide well with the numerical design and simulation. The proposed method provides a simple and effective alternative for NF power redistribution and owns great value in such applications as radio‐frequency identification, wireless power transmission, millimetre‐wave imaging etc.

Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band

“…These solutions are typically used in far-field (FF) applications, while only a few published works may be found on near-field (NF) ones. In [ 18 ], a dielectric transmitarray was proposed to reach a multi-focusing solution, in particular to simultaneously radiate four focused spots. The transmitarray was fed by a single feed; thus, the spots should be far from each other with a broad angular deviation to avoid interferences among them.…”

“…However, when dealing with near-field multi-focusing applications, this type of solution is not used, and published works design transmitarrays, reflectarrays, or metasurfaces using different optimization techniques, which have to include the requirement of each beam in the cost function, therefore increasing the complexity and the computational cost of the design. More recently, in [ 17 , 18 ], two dielectric transmitarrays were proposed to obtain multiples beams. The first one obtains a far-field multibeam solution by using a single feed and a mechanical rotation of the transmitarray itself.…”

“…The first one obtains a far-field multibeam solution by using a single feed and a mechanical rotation of the transmitarray itself. Then, in [ 18 ], a multi-focus transmitarray was proposed to obtain four focused spots simultaneously. The design technique was based on dividing the antenna into several areas, and each of them is associated with a different spot.…”

Fast Transmitarray Synthesis with Far-Field and Near-Field Constraints

“…One case of interest is short-range millimeter wave communications for indoor small cells or femtocells, which could correspond to an office or meeting room. In such a scenario, there might be several devices and sensors closely distributed in the near field (NF) of the base station antennas, and different NF spots are, hence, required to provide coverage to the different devices [3,4], for transfer of information, power (wireless power transfer or WPT), or both (wireless power and information transfer or WPIT). Furthermore, it may also happen that some wireless devices are in the nearby regions of the base station antenna, while others are located in farther positions.…”