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A compact 8-port <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> dual-polarized patch (DPP) antenna array with 8 uncorrelated waves for fifth-generation (5G) Internet-of-Things (IoT) device MIMO antennas in the n79 band (4.4-5.0 GHz) is presented. The 8-Port array has a small size of 51 mm <inline-formula> <tex-math notation="LaTeX">$\times 51$ </tex-math></inline-formula> mm or about <inline-formula> <tex-math notation="LaTeX">$0.59\lambda ^{2}$ </tex-math></inline-formula> with respect to the lower edge frequency (4.4 GHz) of the operating band. The equivalent size per port is <inline-formula> <tex-math notation="LaTeX">$0.074\lambda ^{2}$ </tex-math></inline-formula> only. The small 8-port array size is attributed to each DPP antenna therein with internal grounded metal rods added inside its resonant cavity and additionally four such DPP antennas 90&#x00B0;-sequentially oriented to form the array. The cavity field distribution excited by two ports in each DPP antenna can be modified by the internal grounded metal rods to achieve enhanced port isolation of larger than 15 dB in the operating band. Furthermore, based on using four such DPP antennas 90&#x00B0;-sequentially oriented in the array, the isolation of any two ports in different DPP antennas spaced by a small distance (less than <inline-formula> <tex-math notation="LaTeX">$0.2\lambda $ </tex-math></inline-formula> here) can also be larger than 15 dB, thereby achieving a compact 8-Port array. We further propose to apply it as 8 receive antennas in the IoT device or eXtended Reality (XR) device for receiving 4 spatial MIMO streams (<inline-formula> <tex-math notation="LaTeX">$8\times 4$ </tex-math></inline-formula> MIMO) in the 5G n79 band to obtain high data throughput. In this study, the <inline-formula> <tex-math notation="LaTeX">$8\times 4$ </tex-math></inline-formula> MIMO system [the extreme receive antennas (ERA)-aided MIMO in which the receive antennas outnumber the spatial streams] can have a high data throughput of 3.9 Gbps with 100 MHz bandwidth only. That is, a high spectral efficiency of 39 bps/Hz is obtained, which is about 2.3 times that (about 16.7 bps/Hz) of the <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> MIMO system that has been reported. Details of the compact 8-port <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> DPP antenna array, the modified cavity field distribution technique for enhanced port isolation of the DPP antenna, and the <inline-formula> <tex-math notation="LaTeX">$8\times 4$ </tex-math></inline-formula> MIMO system testing in practical campus public indoor and outdoor scenarios are presented.