Design, Fabrication, and QPSK-Based Validation of a Compact Two-Port MIMO Antenna with Defected Ground Structure for 5 GHz WLAN Applications

This study presents the design, fabrication, and measurement of a compact FR4-based printed monopole antenna and its two-port MIMO configuration for 5 GHz WLAN applications. The single antenna consists of a microstrip-fed chamfered rectangular radiator and a partial ground plane with a narrow defected ground slot. The optimized antenna is mainly evaluated around the 5.5 GHz WLAN region and provides acceptable impedance matching at the target frequency, with simulated and measured S11 values of approximately −10.90 dB and −10.62 dB at 5.5 GHz, respectively. The gain estimated using the substitution method is approximately 1.30 dBi at 5.5 GHz. The antenna is then extended to a symmetrical two-port MIMO structure using a shared partial ground plane and a central I-shaped defected ground structure for coupling reduction. The MIMO results show S11 below −18 dB around 5.5 GHz and an S12 level close to -10 dB, corresponding to approximately 10 dB inter-port isolation. Under the S-parameter-based diversity evaluation, the maximum ECC is approximately 0.01, while the DG remains close to 10 dB. A 2 × 2 OTA QPSK testbed was implemented by connecting both ports of the transmitting and receiving MIMO prototypes to two independent transmit and two independent receive RF chains, respectively. The measured link-level EVM values were 7.4%, 4.8%, and 6.2% at 5.18, 5.50, and 5.825 GHz, respectively. The results show that the proposed antenna provides a practical balance between compact size, simple fabrication, and acceptable WLAN-band MIMO performance.