A Space Efficient Circular Patch MIMO Antenna Having Six Degrees of Freedom for 5G-n79/WLAN Applications

In this article, a single circular patch radiator element of radius 25 mm $\approx ~0.417\lambda _{\mathrm {c}}$ is excited by six $50~\Omega $ co-axial probe feeds spaced equally by ${60}^{0}$ to generate six non-orthogonal polarized decoupled radiations with non-orthogonal pattern diversity to realize a multi-input multi-output (MIMO) antenna having six degrees of freedom. This is further extended to two element MIMO system with inter element spacing of 0.5 mm ( $\approx 0.008\lambda _{\mathrm {c}}$ ), where $\lambda _{\mathrm {c}}$ is the wavelength corresponding to centre carrier frequency 5 GHz. The total size of the proposed design is 101 mm $\times 50.5$ mm $\times 1.55$ mm ( $\approx ~1.683\lambda _{\mathrm {c}} \times 0.842\lambda _{\mathrm {c}} \times 0.026\lambda _{\mathrm {c}}$ ). An acceptable inter port and inter element isolation below -15.2 dB is achieved by loading a simple magneto-electric structure on the patches in the operating range 4.48 GHz to 5.53 GHz which covers 5G-n79, all channels of IEEE 802.11j and few channels of IEEE 802.11a/h/n/ac/ax/be WLAN bands. All the required diversity parameters such as envelope correlation coefficient, diversity gain and mean effective gain ratio are investigated in both uniform and non-uniform media and found within acceptable limit. In addition, channel capacity loss and total active reflection coefficient are studied for multiport MIMO antenna system and found within acceptable limit.