Highly Compact Wideband High-Gain Four-Element MIMO Antenna for 5G New Radio IoT

Wideband millimeter-wave (mm-wave) coverage is essential for the high-speed, low-latency communication required in next-generation 5G New radio (NR) Internet of Things (IoT) systems. This study develops a T-shaped four-element, highly compact wideband multiple-input multiple-output (MIMO) antenna covering the mm-wave n260 (37–40 GHz) and n259 (42–43.5 GHz) bands for 5G NR IoT applications. The antenna is designed on a 0.76 mm-thick Rogers RO4350B substrate with overall dimensions of $28\times $ 28 mm2 ( $3.3\times 3.3~\lambda 2$ ). For design simplicity, a T-shaped patch backed by a full-ground plane is devised to serve as the radiator of a single-element antenna with the dimensions of (Ls $\times $ Ws) mm2, optimized through a systematic three-step design process for improved performance. Moreover, the design has evolved into a $4\times 4$ orthogonal MIMO configuration, achieving improved gain, polarization diversity, and higher data rates, with each element exhibiting wideband characteristics across 11.5 GHz (36.5–48 GHz) with high gains of 9.8 dBi and 6.6 dBi at n260 and n259 5G mm-wave bands, respectively. Additionally, arc-shaped complementary split-ring resonators (CSRR) are integrated into the ground plane to significantly enhance the gain while effectively reducing mutual coupling, remarkably achieving a maximum gain of 9.8 dBi. Furthermore, the MIMO antenna exhibits an envelope correlation coefficient of less than 0.10 between any two MIMO elements encountering the required condition of ¡0.5, ensuring good diversity gain of 9.99 dB, minimum isolation of 18 dB, and total efficiency of 86% at mm-wave n260 band and 89% at mm-wave n259 band. The measured and simulated results are in good agreement, confirming its viability for future 5G mm-wave IoT devices.