Sub-6 GHz MIMO antenna system with enhanced performance based on compact decoupled PIFA pairs for future handheld devices

Abstract

Abstract This study presents a new MIMO antenna design with enhanced bandwidth and minimized mutual coupling, tailored for sub-6 GHz cellular applications. The design consists of eight compact planar inverted-F antennas (PIFAs) with discrete feeding, strategically arranged along the left and right edges of a 75 mm × 150 mm² smartphone PCB using an FR4 substrate. To ensure seamless integration with smartphone circuitry, a single-sided layout is adopted, where both the radiating elements and the ground-connected parasitic structures are printed on the same layer of the substrate. To improve bandwidth and isolation between closely spaced elements (edge-to-edge spacing = 1.5 mm), modified T-shaped stubs are placed between adjacent antennas. The design achieves wideband operation from 3.25 to 4.25 GHz with good impedance matching (S₁₁ < − 10 dB), mutual coupling suppression (~ 13 dB), and excellent diversity metrics such as low envelope correlation coefficient (ECC < 0.05) and total active reflection coefficient (TARC < − 20 dB). The antenna performance remains robust under practical use cases including talk-mode and double-hand scenarios. It also supports a full-ground configuration by repositioning elements along the periphery, with negligible degradation in matching. Further, the link budget analysis confirms reliable communication over long distances (> 1.5 km), accounting for polarization and impedance mismatch losses. Finally, to demonstrate scalability, a broadband mmWave phased array (27–44 GHz) is co-designed on the same PCB, enabling future sub-6 GHz and mmWave 5G/6G smartphone integration. With its compact, wideband, low-SAR and multi-mode operation, the proposed antenna system is a strong candidate for next-generation handheld wireless platforms.