Metamaterial split-ring resonators applied as reduced-size four-port antenna array for MIMO applications

A reduced-size four-port antenna array with highly electromagnetic isolation based on a metamaterial structure is presented. The radiator antenna unit is created using the split ring resonator (SRR) arrangement, which has been widely demonstrated to perform as metamaterial. The metamaterial comportment allows increasing the slow-wave factor on the structure, and as a result, the array size is 42×42mm², where each radiator presents a 52% length reduction compared to a conventional disc monopole with lower cutoff frequency of 2.5 GHz. The separation among elements is very small, achieving values of 0.045λ at the resonance; however, despite the proximity among elements, the electromagnetic isolation reaches values around 30 dB all over the working band. The antenna has a wide bandwidth, going from 2.5 GHz to almost 4 GHz. The array performs a very low Envelope Correlation Coefficient (ECC), achieving levels lower than 0.035 and a steady Total Active Reflection Coefficient (TARC), obtaining a system bandwidth of 1.38 GHz for a TARC ≤−10dB, resulting a suitable structure for Multiple-Input Multiple-Output (MIMO) applications.