In this article, a planar compact grounded coplanar waveguide (GCPW)-fed 4-element multiple-input multiple-output (MIMO) antenna array with a defected ground structure (DGS) is demonstrated for fifth generation (5G) millimeter-wave (mmWave) communication. Each element of GCPW-fed mmWave MIMO antenna array contains a deformed pentagon-shaped radiating patch etched with a pair of identical circular slots in top surface and a DGS in bottom surface. To maintain low design complexity and compactness, a DGS is introduced and formed by embedding dual asymmetrical inverted T-shaped slots in the partial ground plane which enhance the gain and bandwidth of the antenna. The equivalent circuit model of the proposed DGS loaded GCPW-fed antenna is realized and presented. The proposed 4-element mmWave MIMO antenna array is realized by arranging the 4 identical antenna elements horizontally in a row with a distinct gap without any decoupling structure. It has the size of 1.02λ × 3.86λ × 0.021λ (at 25.66 GHz) and exhibits the measured bandwidth of 49.62% (25.30-42.0 GHz) with a peak gain of 12.02 dBi. Furthermore, the envelope correlation coefficient (ECC) < 0.0014, isolation > 24 dB between antenna elements, and channel capacity loss (CCL) < 0.29 bits/sec/Hz of the mmWave MIMO antenna array are attained over the entire mmWave frequency band.
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