Swarm intelligence driven inverse design of slot patterns for sub-6 GHz 5G MIMO antennas in virtual reality applications

This paper presents an efficient approach for developing miniature sub-6 GHz 5G MIMO antennas with enhanced bandwidth and high isolation. Utilizing the capabilities of particle swarm optimization (PSO) on a pixelated surface, an objective function is formulated to minimize the reciprocal of the bandwidth while ensuring that the reflection coefficient (|S-11|) remains below -10 dB and the transmission coefficient (|S-21|) is below -20 dB. This methodology effectively eliminates the necessity for incorporating complex decoupling networks to enhance isolation. The inverse design concept is independently implemented in the slot arrangements of two different configurations of 2-element MIMO antennas: one in which the individual antenna components are placed in an antiparallel orientation, and the other in which they are arranged orthogonally. The optimized designs, measuring 24 x 48 (0.4 lambda(o) x0.8 lambda(o)) mm(2) in size, yield operating spectra spanning from 4.53 GHz to 7.01 GHz for the orthogonal scenario and 3.95 GHz to 5.15 GHz for the antiparallel orientation in free space. An ECC <0.0173 and MEG <-6 dB, observed in the operating bandwidth, supports satisfactory MIMO antenna diversity performance. Having negligible current coupling between ports, these MIMO antennas, with a diversity gain of close to 10 dB are well-suited for integration into virtual reality (VR) headsets. In situ path loss measurement campaign was executed by integrating the antenna into participants' virtual reality headsets. The performance of the proposed MIMO antenna has been tested through numerical analysis, equivalent circuit modeling, and measurement campaigns using fabricated prototypes. Experimental results from testing the prototypes closely align with the simulations, confirming the effectiveness of the proposed designs both in free space and in proximity to the human body.