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A tree-shaped graphene based microstrip MIMO antenna for terahertz applications is proposed.The proposed MIMO antenna is designed on a 600×300 μm 2 polyimide substrate. The designed MIMO antenna exhibits a wide impedance bandwidth of 88.14% (0.276 -0.711 THz) due to the suggested modifications in the antenna configuration. The MIMO design parameters like total active reflection coefficient (TARC), mean effective gain (MEG), envelope correlation coefficient (ECC) and diversity gain (DG), Channel capacity loss (CCL) are evaluated and their values are found within acceptable limits. The proposed MIMO structure offers MEG ≤ −3.0 dB, TARC≤ -10.0 dB, DG≈ 10 dB, CCL < 0.5 bps/Hz/sec and ECC < 0.01 at the resonant frequency. At the resonant frequency, the isolation between the radiating elements of the proposed MIMO is recorded as −52 dB. The variations in operating frequency and S-parameters are also analyzed as a function of the chemical potential (μc) of the graphene material.The parametric analysis, structural design evolution steps, surface current distribution, antenna characteristics parameters and diversity parameters are discussed in detail in this paper. The designed MIMO antenna is suitable for high speed short distance communication, video rate imaging, biomedical imaging, sensing, and security scanning in the THz frequency band.

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Summary The proposed research work is on fractal MIMO antenna with microstrip feeding for lower sub‐6 GHz. The design construct's goal is to improve the isolation among the patches and is constructed with a combination of circular strip and rectangular strip slots, and rectangular slots are introduced on the ground plane. The fractal‐shaped MIMO structure composes of FR‐4 material and compact size of 25 × 35 mm2. The current 2 × 1 fractal MIMO radiator resonates at a frequency 3.5 GHz for lower sub‐6‐GHz applications with directional radiation patterns. In this structure, the performance characteristics of design antenna parameters like S‐parameters, surface current distributions, and radiation pattern of the fractal MIMO radiator are investigated. In addition to antenna parameters, MIMO parameters like diversity gain (DG), mean effective gain (MEG), channel capacity loss (CCL), total active reflection coefficient (TARC), and time‐domain analysis parameters are also evaluated. It has been observed that the MIMO parameters of the antenna are in the acceptable range. Fractal‐based prototype MIMO structures are fabricated as well as tested for effective radiation and impedance. The improvised MIMO design that's been installed on a printed circuit board with connector, device housing, compact size, and various types of housing shows better performance compared to the conventionally designed antennas.

For lower sub-6 5G applications, a two-element crescent angular ring antenna is proposed. The suggested Multiple-Input-Multiple-Output (MIMO) antenna has a dimension of 38 × 25 mm 2 , a substrate height of 1.6 mm, and dielectric material of FR-4 (lossy) with a dielectric constant of 4.4 and a loss tangent of 0.002. For 50-Ω impedance matching, a line feed approach is used to improve return loss and achieve −35 dB at 3.5 GHz. Furthermore, there is a fractional bandwidth from 3-6.5 GHz (116.6%) using a monopole ground plane maintained with |S 11 | < −10 dB. Changing the placements of the radiators improves isolation by −42 dB. For the current crescent shape, the MIMO structure showed a radiation efficiency and gain of 84.25% and 6.2 dBi. Finally, the performance of MIMO metrics of the crescent shape structure like ECC, diversity gain, channel capacity loss, TARC, and mean effective gain is evaluated in addition to good radiation characteristics.