## 1 Introduction  
Throughout the last few decades, near-field focusing (NFF) techniques have risen in popularity as an approach to concentrate the power density of the antenna on a point within the outer boundary \(2D^{2}/\lambda\), where \(D\) is the antenna aperture. NFF antennas have received great interest in several application such as radio frequency identification (RFID) [1, 2], microwave imaging [3, 4], or medical hyperthermia [5, 6]. Recent applications such as wireless power transfer (WPT) or 5G communications have led to emerging needs for high efficiency wireless communications between multiple devices and sensors, mostly closely distributed and within the near-field region of their antennas. Either NFF or multi-focusing techniques are preferred to improve these application performances since they should only radiate energy therein the devices are located, increasing the efficiency. A popular approach in NFF design is the conjugate phase (CP) used to adjust the phase of the antenna elements such that the radiated wave is in phase at a single focal point [7, 8]. However, when dealing with multi-focusing solutions, other approaches may be used. A classical solution for planar arrays is to use optimization techniques to minimize a cost function with requirements for all the spots simultaneously; nonetheless, the increase of the computational cost regarding the CP and the complexity and high insertion losses of the feeding networks makes this approach unsuitable in the millimeter band. Recently, spatially-fed antennas, such as reflectarrays or transmitarrays (TAs) [9, 10], phased arrays [11], or Fresnel zone plates (FZPs) [12], have been considered to overcome these limitations, taking advantage of their capability to shape the incoming phase front of a conventional antenna. Hence, a multibeam pattern can be accomplished through selecting the feed appropriately. In [13], a graded index lens is fed by a multiple-port stacked-patch feed, achieving four different and independent beams. These solutions demand the design of a dedicated feed, not a conventional one. A straightforward approach is based on a feed displacement using a mechanically movable feed to obtain multiple independent beams, the direction of which is determined by the feed position. This solution has been successfully applied to transmitarrays and reflectarrays for space communications [14; 15; 16]. 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. 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. This approach is suitable when a large aperture can be employed and spots are far from each other (broad angular deviation), but this is not the case. In this work, a planar dielectric-only transmitarray is evaluated for near-field multi-focusing applications in the Ka-band. The transmitarray design process is based on the analytical approach of the conjugate phase for a single-center feed configuration. Then, alternative to a mechanical displacement of the feed, the transmitarray is illuminated by a cluster of horn antennas working at 28 GHz, but different shifted carriers or switching the horn antennas in different time slots, avoiding any interference between beams. Thus, the number of focused spots obtained is equal to the number of feeds.