Two-element MIMO antenna system for multiband millimeter-wave, 5G mobile communication, Ka-band, and future 6G applications with SAR analysis

A two element multiband multiple-input multiple-output (MIMO) antenna system with low specific absorption rate is proposed for Ka-band space satellite, millimeter-wave (mm-wave), fifth-generation (5G), and future sixth-generation (6G) wireless communication applications. The essential characteristics of both 5G and future 6G communications can be fulfilled by the proposed MIMO antenna design. The proposed MIMO antenna system has significant advantage of covering four relevant and usable frequency bands, i.e., 16 GHz, 25.5 GHz, 28 GHz, and 32 GHz used for the above mentioned applications. The design of the presented antenna looks like a vertical Yagi-Uda antenna with L-shaped ladder. Moreover, two circular slots and a slotted vertical stub are etched in a partially shared ground. The complete electrical dimension of the presented antenna is 6.8 lambda(0) x 5.7 lambda(0) x 0.068 lambda(0), calculated at resonating frequency 25.5 GHz, where lambda(0) is wavelength in free space. The geometry of the presented antenna is fabricated using Rogers RO4350TM with dielectric constant (epsilon(r)) of 3.48, a loss tangent of 0.0025, and the substrate thickness of 0.8 mm. The presented MIMO antenna is excited with a 3 mm wide microstrip feed line having 50 Omega characteristics matched impedance. In terms of performance, the proposed antenna has achieved a reflection coefficient < - 10 dB, and isolation < -15 dB in all the resonating bands, radiation efficiency varies 72%-84%, impedance bandwidth of 4.6 GHz, 1.5 GHz, 1.11 GHz, and 7.5 GHz, and realized gain of 10.18, 12.05, 13.07, & 5.55 dBi is also achieved at frequencies 16 GHz, 25.5 GHz, 28 GHz, and 32 GHz. The achieved values for various MIMO matrices are envelope correlation coefficient > 0.0048, diversity gain of 9.98 dB, channel capacity loss < 0.00023 bits/s/Hz, and mean effective gain < -6 dB. The simulated results obtained by ANSYS I 2022 R2 (HFSS) and the experimental results measured by vector network analyzer (VNA) show a good agreement.