Design and Analysis of a 4-Element Compact MIMO Antenna for 5G n78/n79/n48 Band Communication

Abstract

This paper presents an irregular polygon design with a unique protruding strip that has been specifically developed for 5G NR n78/n79/n48 applications, resulting in a compact and efficient 4-element MIMO antenna. The antenna measures 31.25 × 41.25 × 1.6 mm³, utilizing an FR-4 substrate with a ε_r of 4.4. It achieves a wide impedance bandwidth (S_xx < −10 dB) covering the 3.15–3.89 GHz frequency range. The structure includes a 2-element MIMO antenna with elements spaced just 0.012 λ0 apart, paired with another orthogonally arranged 2-element MIMO antenna. The design employs a microstrip feeding line with a partially truncated ground, complemented by embedded grounded stubs to enhance isolation. Additionally, T- and I-shaped decoupling elements positioned between the radiators further extend the bandwidth and improve isolation (S_xy) across the band. Despite its compact size, the antenna effectively reduces coupling, achieving isolation levels (S_xy) better than −18.25 dB throughout the operating range. It delivers a peak gain of 3.79 dBi and boasts an excellent radiation efficiency of 86%–92%. The MIMO performance is characterized by a total active reflection coefficient (TARC) of −10 dB, a mean effective gain (MEG) of 1 dB, and a channel capacity loss (CCL) of below 0.175 bits/s/Hz. The antenna also demonstrates an outstanding envelope correlation coefficient (ECC) of 0.028 and a diversity gain (DG) of 9.9 dB, making it highly suitable for 5G NR n78/n79/n48 communication applications.