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This article presents a symmetrical reduced-size eight-element MIMO antenna array with high electromagnetic isolation among radiators. The array utilizes easy-to-build techniques to cover the n77 and n78 new radio (NR) bands. It is based on an octagonal double-negative metamaterial split-ring resonator (SRR), which enables a size reduction of over 50% for the radiators compared to a conventional disc monopole antenna by increasing the slow-wave factor. Additionally, due to the extreme proximity between the radiating elements in the array, the modal significance (MS) method was employed to identify which propagation modes had the most impact on the electromagnetic coupling among elements. This approach aimed to mitigate their effect by using an electromagnetic barrier, thereby enhancing electromagnetic isolation. The electromagnetic barriers, implemented with strip lines, achieved isolation values exceeding 20 dB for adjacent elements (MS method. The elements are arranged in axial symmetry, forming an octagon with each antenna port located on a side. The array occupies an area of 0.32 λ2 at 3.5 GHz, significantly smaller than previously published works. It exhibits excellent performance for MIMO applications, demonstrating an envelope correlation coefficient (ECC) below 0.0001, a total active reflection coefficient (TARC) lower than −10 dB for various incoming signals with random phases, and a diversity gain (DG) close to 20 dB.

In this paper, a novel structure of two interlaced antenna arrays for MIMO applications is presented. It consists of two 2 × 1 triangular patch array antennas, which have all elements separated by a short distance among them (0.22λ0), where mutual coupling can be very poor (S21 = -7.81 dB). To overcome such weakness, a simple and efficient method is used: one neutralization line (NL) is introduced to increase the decoupling between both ports, reaching up to -29 dB at the central frequency, and below -20 dB over a large bandwidth. The whole MIMO antenna array has dimensions of 1.56λ0 × 0.3λ0 and has a gain of 9.11 dBi. Its diversity parameters describe it as a useful radiator for MIMO communications systems. [ABSTRACT FROM AUTHOR]