Hybrid technique-based circularly polarized MIMO antenna with low mutual coupling for millimeter-wave communications

This research introduces an innovative hybrid approach for developing a circularly polarized (CP) multiple-input multiple-output (MIMO) antenna designed for millimeter-wave (mm-wave) band applications. The proposed CP-MIMO antenna consists of four orthogonal rectangular slotted radiators, a hexagonal ring hybrid coupler-shaped parasitic element (HRHCP), and a rear Jerusalem cross-shaped decoupling ground (JCDG). A small antenna measuring 35 × 35 × 0.508 mm³ (3.15λ₀ × 3.15λ₀ × 0.0457λ₀) is realized by multiple techniques, including slots in the radiator, dielectric guiding, and parasitic elements, with λ₀ denoting the free space wavelength at 27 GHz. The decoupled arrangement effectively minimizes the distance between the two radiators to 0.212λ₀. The integration of a JCDG and HRHCP component among the MIMO antenna radiators enables the implementation of an effective decoupling technique aimed at mitigating the effects of mutual coupling (MC). The simulated outcomes of the proposed antenna with decoupling exhibit improved S-parameters, with |S₁₁| < -10 dB throughout the frequency range of 24.23 to 29.02 GHz. The MIMO antenna has a low MC of |S₁₂| at -29 dB and a 3-dB axial ratio (AR) spanning from 26.1 to 28.5 GHz. The proposed antenna demonstrates a maximum gain of 7.0 dBi in the lower frequency range and 7.5 dBi in the higher frequency band. An equivalent circuit model (ECM) is created for both single and MIMO layouts, providing a more detailed analytical insight. The experimental data are appropriately compared with the simulated data. The proposed architecture is optimal for 5G, satellite, and mm-wave applications, where compactness, low MC, and enhanced AR bandwidth are critical.