Wide band THz MIMO antenna with isolation prediction using machine learning algorithms for IoT applications

In this paper, a compact wideband two-port multiple-input-multiple-output (MIMO) antenna is presented which operates in the Terahertz (THz) range specifically at 1.58 THz and 2.6 THz. The proposed design is based on a polyimide substrate (ε r = 3.5, tan δ = 0.003) with a graphene patch radiator and copper ground plane to be used in Internet of Things (IoT) applications. The single-element antenna is developed in four progressive design steps, rectangular patch, corner-chamfered octagonal patch, ring-frame with central aperture and finally, cross-slot (plus-sign) loaded octagonal structure, which has two resonances analyzed at 1.6 THz (S11 = − 32 dB) and 2.35 THz (S11 = − 53 dB). Systematic optimization of the MIMO configuration is done by three placement configurations, and the optimized configuration exhibits an inter-port isolation of up to − 18 dB in the range of 2.6 THz and − 25 dB to − 45 dB in the range of 1–1.5 THz, gain of 6–6.5 dBi over the operating bands. A comprehensive analysis of MIMO diversity has shown in terms of envelope correlation coefficient (ECC) of less than 0.005, a diversity gain (DG) of 9.9–10 dB, a channel capacity loss (CCL) of less than 0.5 bits/s/Hz and a total active reflection coefficient (TARC) of less than − 10 dB. In order to overcome the computational cost of large-scale parametric sweeps, the supervised machine learning (ML) surrogate model is built to predict inter-port isolation (S21) as a function of frequency and inter-element spacing, which helps to minimize the computational load of repeated parametric full-wave HFSS analysis. The hyperparameter optimization of gradient boosting regressor obtains R 2 of 99.99%, MAE of 0.26 dB, and RMSE of 0.37 dB for the held-out test data, outperforming all baseline regression models, making the Gradient Boosting Regressor with Optuna hyperparameter optimization a reliable surrogate model for the isolation prediction of THz MIMO antenna analysis.