Compact Two-Port Dual- and Triple-Band MIMO Antennas With Orthogonally Placed Microstrip Monopole Elements for 5G N77/78/79 Sub-6-GHz Applications

Abstract

In today's wireless communication landscape, the demand for compact MIMO antennas with low mutual coupling is critical. To meet this requirement, this paper presents two compact MIMO antenna configurations based on microstrip line principles. Initially, a compact dual-band antenna is designed for 5G N77/N78/N79 sub-6-GHz applications. The introduction of an inverted L-shaped slot into the broadband radiating element enables the generation of two distinct resonances. Without the slot, the antenna covers a broad frequency range from 4.30 to 5.54 GHz. Upon slot insertion, it achieves dual-band operation across 3.3–3.78 GHz and 4.3–5.15 GHz. Subsequently, by integrating an additional inverted L-shaped slot on the opposite lateral side, a triple-band response is realized, covering 3.6–3.85 GHz, 4.75–5.05 GHz, and 5.3–7.5 GHz. Both antenna designs are fabricated on an FR-4 substrate (εᵣ = 4.4, tanδ = 0.025) with 1.6 mm thickness and a compact footprint of 23.3 × 29.125 mm² (0.37λ₀ × 0.46λ₀). The radiating structure possesses an inverted T-shaped geometry occupying (8 × 9.65) + (29.125 × 13.65) mm² that meets the requirements for modern space-limited devices. Furthermore, two compact two-port MIMO configurations (23.3 × 66.06 mm², or 0.37λ₀ × 1.04λ₀) are proposed, utilizing orthogonally placed dual-band and triple-band monopole elements. Electromagnetic simulation using Ansys HFSS confirms that the designs achieve excellent MIMO performance, including envelope correlation coefficients (ECC) below 0.0019 and 0.001, channel capacity loss (CCL) under 0.26 and 0.46 bits/s/Hz, peak gains of 4.9 and 5.1 dBi, and radiation efficiencies exceeding 94% and 85%, respectively, for MIMO antennas with dual-band and triple-band monopole antenna elements. Notably, mutual coupling remains below −23 dB and −24.5 dB across the operating bands, despite maintaining an edge-to-edge spacing of less than 0.125λ.