Near field multifocusing on antenna arrays via non‐convex optimisation

Abstract

An optimisation framework for near field multifocusing on antenna arrays is proposed. Its aim is to obtain the feeding weights that must be applied to the elements of the array so that the antenna focuses on two or more targets simultaneously. The method is based on the definition of a proper cost function, which is minimised using an optimisation algorithm over an equivalent least squares problem. The success of the technique is noted in the fact that different array parameters can be obtained: magnitude and phase of the array elements or only phase synthesis. In order to show the efficiency of the method, several tests are carried out using different arrays and optimisation parameters. The simulation, manufacture and measurement of an 8 × 8 planar array able to focus on two different targets is also performed. Results show how the framework can be applied to general arrays and demanding requirements, so it may be easily extended to different synthesis problems besides multifocusing.

General Near Field Synthesis of Reflectarray Antennas for Their Use as Probes in Catr

“…Due to the generality of the proposed framework for general near field optimization, in which the specifications are given in form of maximum and minimum templates, and in which both the amplitude and phase of the near field are taken into account, the proposed technique may be used for other near field applications, such as RFID [11], imaging [12], microwave virus sanitizer [13] or multi-focusing [20], by adapting the cost function (for instance, setting the phase cost to zero if the near field phase does not play a role) and providing suitable templates.…”

“…This model is then employed in a near field Phase-Only Synthesis (POS) to improve the quiet zone generated by the reflectarray antenna. The chosen algorithm is the Levenberg-Marquardt (LMA), which has been effectively used in array synthesis with success [20][21][22][23][24][25][26][27], and it takes into account both amplitude and phase of the near field, since CATR requirements impose a maximum allowable ripple in both, making it a more challenging task than an amplitude-only synthesis. The optimization is performed in several near field planes, flattening the amplitude and phase, greatly improving the size of the quiet zone.…”

Reflectarray probe optimization at millimeter frequencies

“…The LMA [10] has been chosen as the optimization algorithm in order to perform the POS. Since the complex near field is to be optimized, both amplitude and phase have to be taken into account into the cost function.…”

Retro-Directive Beamforming Versus Retro-Reflective Beamforming With Applications in Wireless Power Transmission

“…Leaky-wave lens is another type of well-studied configuration to achieve near-field focusing [9][10][11]. Many researchers take advantage of planar antenna array (composed of microstrip elements, for instance) to achieve focusing in the near-zone [12][13][14][15][16][17][18][19][20]. Compared to the above methods, retro-reflective beamforming technique focuses electromagnetic fields with the aid of pilot signal such that the focal point coincides with the location from which the pilot signal is broadcasted, thus is more suitable for wireless power transmission applications [3,21,22].…”