Design of a compact four-element MIMO antenna with high isolation for millimeter-wave applications

Abstract

This paper presents a compact 8 × 8 mm2 four-element Multiple Input Multiple Output antenna for 5 G frequency range (FR-2) operating over 23.68–31.88 GHz, derived from a mathematically shaped microstrip radiator on Rogers RT5880 with a partial-ground topology. The 4 × 4 × 0.25 mm3 (0.36λ0 × 0.36λ0 × 0.023λ0) single element is tiled into an 8 × 8 × 0.25 mm3 (0.72λ0 × 0.72λ0 × 0.023λ0) array arranged orthogonally to achieve inherent isolation without external decouplers. Parametric optimization of ground height/width and feed width yields a fractional bandwidth (BW) of 27.2% with deep minima near 27.1 GHz; inter-element coupling (isolation) stays below −23 dB across the entire operating band. Diversity metrics computed from far-field shows envelope correlation coefficient less than 0.002 and diversity gain >9.99 dB across operating BW, while channel capacity loss remains well below typical limits. System-level assessments indicate mean effective gain tightly clustered near −3 dB for all ports, and total active reflection coefficient (TARC) exhibits −32 dB notch near 27–28 GHz with TARC < −10 dB over a practical span. The simulated and experimental results demonstrate wideband matching, low correlation, and efficient active power acceptance in a compact footprint, suitable for dense 5 G devices in the 28 GHz band.