-A mutual coupling reduction strategy that employs meta-structures is introduced for wideband, dual-polarized, high-density, planar, patch antenna arrays. The meta-structures consist of two types of resonators: grounded capacitively loaded loops (GCLLs) and π-shaped elements. By incorporating the meta-structures into the array configuration, the isolation levels between adjacent radiating elements in both the E-and H-plane orientations are improved by as much as 7.15 dB. The surface current distribution behaviors of the array with only the GCLLs and with only the π-shaped elements are investigated thoroughly to explain the mutual coupling reduction mechanisms. A proof-of-concept array was constructed and tests were performed that validate the reported design principles and simulation results. M. (5G) communication systems [1,2]. It has several unique advantages that arise from its ability to facilitate the presence of additional signal channels instead of requiring the use of extra frequency spectrum or power. Benefits include being able to increase the data capacity and to make the system more adaptable.
Index TermsMIMO approaches are based on antenna arrays. With the ever increasing demand for more capacity, it is anticipated that massive MIMO will be central to 5G systems; and it will be facilitated by compact dense arrays. However, strong inter-element coupling occurs when the element spacing is small; it dramatically increases the spatial correlations and seriously deteriorates the signal-to-interference-plus-noise -ratio (SINR) [3]. Consequently, mutual coupling effects between array elements have attracted intense attention.There exist a plethora of reported approaches that are capable of reducing the mutual coupling in the physical layer. However, because of known fundamental physical limitations [4], it cannot be eliminated completely. Nevertheless, mutual coupling reduction can significantly improve the performance of MIMO systems.In general, the existing, most widely used mutual coupling reduction strategies can be classified into the following three categories. One approach focuses on introducing a variety of compact isolation elements between the radiators. The choices have been rather diverse. They include parasitic elements, such as monopoles [5], scatterers [6], and radiation patches [7]. Also, they include electromagnetic band-gap (EBG) structures, such as mushroom-like EBG structures [8], F-shaped EBG structures [9], and uniplanar compact EBG structures [10,11]. Defected ground structures (DGSs), such as periodic rectangular slits [12], back-to-back U-shaped slots [13], T-shaped slots [14], and loop slots [15] have also been used. More recently, numerous metamaterial-inspired structures have been considered, such as folded single split ring resonators [16], grounded split-ring resonators (GSRRs) [17], multiple split-ring resonators (MSRRs) [18] While the above strategies have reduced mutual coupling, one witnesses certain drawbacks accompanying each of them. As a result, their widespre...