volume | PIER Journals

Abstract

This paper presents the design, optimization, fabrication, and experimental validation of a compact 2 × 2 microstrip Multiple-Input Multiple-Output (MIMO) antenna for 5G sub-6 GHz applications. The proposed antenna is centered at 5.5 GHz and implemented on an FR4 substrate with an overall size of 60 × 60 mm², making it suitable for integration into modern compact wireless devices. The design process begins with the development of a single Planar Microstrip Monopole Antenna (PMMA), which is enhanced using a systematic stub-loading technique to improve impedance matching, radiation stability, and efficiency. The optimized element is then replicated and arranged using an orthogonal placement strategy to reduce mutual coupling without employing additional decoupling structures or parasitic components. The proposed MIMO configuration achieves excellent impedance matching, with a measured reflection coefficient of approximately -49 dB at 5.5 GHz and an operational bandwidth extending from 4.7 to 6.49 GHz. The antenna exhibits high radiation efficiency (≈81) and total efficiency (≈79) within the operating band. The measured peak gain reaches 4.70 dBi, showing close agreement with simulated results. Diversity performance is confirmed by an extremely low envelope correlation coefficient (ECC < 0.0001) and a diversity gain approaching 10 dB, indicating strong spatial diversity and reliable multipath performance. Furthermore, the Total Active Reflection Coefficient (TARC) remains below -10 dB across the main operating region, validating stable multi-port excitation behavior. The combination of compact size, high efficiency, excellent isolation, and low structural complexity demonstrates that the proposed antenna provides a practical and cost-effective solution for sub-6 GHz 5G MIMO systems.

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Mr. Hayder Majid Mutashar

Prof. Mohammad Sajjad Bayati