Wearable and ultra-compact mm-wave four port MIMO antenna for dual band n261 and n260 (28/38) GHz 5G applications

This paper introduces a highly effective four-port MIMO antenna that is both compact and powerful. This antenna is specifically designed to cater to dual-band 5G applications at the frequencies of 28/38. The antenna radiating electromagnetic energy employs a single element that operates seamlessly at both resonant frequencies mentioned while having a compact size of 9.5 mm x 7.5 mm Rogers/Duroid RT-5870 laminate, which boasts a thickness of 0.254 mm. Slot etching and stub insertion techniques are employed, and the antenna's dimensions are adjusted to achieve resonance at certain frequencies. This resulted in a peak realized gain of over 5 dB for both the 28 GHz and 38 GHz frequencies, using just one antenna element. The element is then examined for three different two-port configurations to determine the optimal arrangement for maximum isolation. Finally, the design was expanded to a four-port MIMO with elements placed in a unique proposed configuration having dimensions of 15 x 15 x 0.254 mm3. Spatially and uniquely configured elements provided the isolation of less than -20 dB for required bands having measured MIMO parameters within the standard acceptable values. Recorded values of the measured envelope correlation coefficient (ECC) are found to be less than 0.1 at both 28 GHz and 38 GHz frequencies. Moreover, the diversity gain (DG) is greater than 9.95 dB at 28 GHz and over 9.99 dB at 38 GHz, while the total active reflection coefficient (TARC) is less than 0 dB for both frequencies. The channel capacity loss (CCL) has also been found to be less than 0.2 bits/s/Hz. The proposed single element and the four-port design are also analyzed for conformality which witnessed a minor change in impedance bandwidth at a bent of 15 degrees, 25 degrees, 35 degrees and 45 degrees making it applicable for wearable devices in the 5G spectrum. The specific absorption ratio for single as well as four ports is also found to be much less than the standard acceptable values making the antenna useful for embedded and wearable devices for humans. The four-port MIMO is reported with an SAR value of 0.0105 W/Kg at 28 GHz and SAR of 0.0416 W/Kg at 38 GHz making the antenna safe for embedded devices for wireless communication.