Compact Four-Port Ku-Band MIMO Antenna with Enhanced Isolation Using Modified DGS for Early-Phase 6G Applications

This paper presents a compact four-port multiple-input multiple-output (MIMO) antenna operating in the Ku-band around 13 GHz, targeting early-phase 6G upper-midband front-end applications. The proposed antenna employs orthogonally arranged short-ended square patch elements combined with a modified defected ground structure (DGS) to achieve high port isolation and compact footprint. A prototype fabricated on Rogers RO4350 substrate demonstrates good agreement between simulated and measured results. The antenna achieves $|S_{11}|$ < −10 dB over 12.9–13.1 GHz band, inter-port isolation exceeding 25 dB, and an envelope correlation coefficient (ECC) below $0.01$. The measured realized gain reaches 7.02 dBi with a radiation efficiency above 80%. Compared with recent Ku-band MIMO antennas, the proposed design provides a 45% size reduction while maintaining high isolation at a close element spacing of 0.25${\lambda }_0$. The proposed antenna intentionally adopts a narrowband operating characteristic, reflecting a design trade-off that prioritizes compact size, high isolation, and low spatial correlation over wideband performance. These features make the antenna well suited for early-stage 6G-oriented front-end modules, fixed wireless access, backhaul links, and short-range sensing systems operating in the upper-midband frequency range.