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 x 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 4x4 MIMO access-point application is presented. The four-port SPA is an all-metal structure with a small-size square patch (50 mm x 50 mm, about 0.41 lambda x 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 gapcoupled 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 TM1/2,1/2 mode or the TM1/2,1/2-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.