Compact circular MIMO antenna with defected ground structure (DGS) for improved isolation in 5G sub-6GHz mobile systems

Abstract

• A compact circular MIMO antenna with Defected Ground Structure (DGS) is designed for enhanced isolation in 5G sub-6 GHz mobile systems. • The antenna achieves a 3.5 GHz impedance bandwidth (3.0–6.5 GHz), covering key 5G bands (n77, n78, n79) with a peak gain of 11.5 dBi and 95% efficiency. • A rectangular DGS improves isolation, reducing mutual coupling to -53 dB, with simulated and measured results confirming low coupling (-15 to -55 dB). • MIMO metrics (DG, ECC, TARC) and SAR analysis confirm suitability for handheld 5G systems. This work introduces a compact circular MIMO antenna designed specifically for sub-6 GHz 5G mobile applications. The antenna features two circular radiating elements arranged orthogonally to each other, incorporating a circular ring and additional side stubs to enhance both bandwidth and impedance matching. A partially slotted ground plane with curved cuts is employed to reduce capacitive effects and further extend the operational bandwidth. The design is implemented on an FR4 substrate with compact dimensions of 0.3λ₀ × 0.6λ₀ × 0.0242λ₀ at 4.5 GHz, achieving a wide impedance bandwidth of 3.0 to 6.5 GHz—covering major 5G frequency bands such as n77, n78, and n79. To improve port isolation, a rectangular defected ground structure (DGS) is introduced, effectively reducing mutual coupling down to -53 dB. Both simulated and experimental results show excellent isolation performance (ranging from -15 dB to -55 dB), high radiation efficiency of up to 95%, and a peak gain reaching 11.5 dBi. Evaluation of MIMO characteristics—including Diversity Gain (DG), Envelope Correlation Coefficient (ECC), and Total Active Reflection Coefficient (TARC)—confirms the antenna's suitability for multi-port systems. Additionally, Specific Absorption Rate (SAR) analysis demonstrates compliance with safety standards for handheld device integration. Overall, the proposed antenna offers a robust solution for modern sub-6 GHz 5G communication systems.