Orthogonal eight-element MIMO antenna for dual-band 28/38 GHz mmWave communications

• Design of a compact eight-element MIMO antenna operating at dual frequency bands of 28 GHz and 38 GHz for 5G mmWave communications. • Orthogonal placement strategy achieves high isolation ( > 25 dB at 28 GHz, > 20 dB at 38 GHz) without additional decoupling structures. • Excellent diversity performance with envelope correlation coefficient • Comprehensive system-level evaluation including channel capacity, link margin, and received power analyses. • Compact size of 33.8 x 33.8 mm 2 with measured peak gains of 5.88 dBi at 28 GHz and 4.89 dBi at 38 GHz. A critical challenge in realizing high-performance multiple-input multiple-output (MIMO) systems at millimeter-wave (mmWave) frequencies is mutual coupling. This paper presents a compact eight-element MIMO antenna operating at 28 GHz and 38 GHz that effectively suppresses mutual coupling without requiring any additional decouplers. The design begins with a slotted patch element and then by arranging eight such elements in an orthogonal configuration, spatial diversity is exploited to achieve strong isolation and pattern diversity. The MIMO antenna has dimensions of only 33.8 × 33.8 mm 2 ( 3.16 × 3.16 λ 0 2 at 28 GHz and 4.29 × 4.29 λ 0 2 at 38 GHz). Measured results validate dual-band performance with impedance bandwidths of 26–29 GHz (fractional bandwidth 10.9%) and 36.07–39.1 GHz (fractional bandwidth 8.1%), peak realized gains of 5.88 dBi and 4.89 dBi, and port isolation more than 25 dB and 20 dB at 28 GHz and 38 GHz, respectively. Excellent MIMO diversity performance is confirmed by envelope correlation coefficient (ECC) < 0.05, diversity gain (DG) > 9.90 dB, and total active reflection coefficient (TARC) less than - 10 dB across both bands. System-level evaluations of channel capacity, link margin, and received power further demonstrate the practical viability of the proposeed MIMO design. With its compact size, self-decoupled design, and good diversity characteristics, the proposed MIMO antenna is suitable for integration into mmWave 5G mmWave compact user terminal and phased array systems.