Decoupling Hybrid Metal Walls and Half-Wavelength Diagonal Open-Slots Based Four-Port Square Patch Antenna With High Port Isolation and Low Radiation Correlation for 2.4/5/6 GHz WiFi-6E 4 × 4 MIMO Access Points

Based on applying the hybrid metal walls and half-wavelength diagonal open-slots, a four-port square patch antenna (SPA) having high port isolation (>20 dB) and low radiation correlation (envelope correlation coefficients < 0.01) for 2.4/5/6 GHz (2.4-2.5/5.15-7.125 GHz) WiFi-6E $4\times 4$ MIMO access-point application is presented. The four-port SPA is an all-metal structure with a small-size square patch (50 mm $\times50$ mm, about $0.41\lambda \times 0.41\lambda $ at 2.45 GHz) mounted 11 mm above a ground plane. Between the square patch and the ground plane, the hybrid metal walls consisting of an outer shorting metal wall and an inner gap-coupled metal wall are placed along the patch’s two centerlines to create four isolated resonant quadrants for the four ports. Each resonant quadrant can support the TM $_{\mathrm {1/2,1/2}}$ mode or the TM $_{\mathrm {1/2,1/2}}$ -like mode in the 2.4 GHz and 5/6 GHz bands. Owing to the inner gap-coupled metal wall, enhanced port isolation between two adjacent ports can be obtained. Additionally, enhanced port isolation between two opposite ports is obtained by embedding two half-wavelength open-slots (length about $0.5\lambda $ at 2.45 GHz) along the patch’s two diagonal lines. The decoupling hybrid metal walls and half-wavelength diagonal open-slots together enhance the port isolation of the four ports to be larger than 20 dB over the 2.4 GHz and 5/6 GHz bands. The antenna structure and operation principle of the proposed four-port SPA are described. Experimental results of the fabricated prototype are also presented.