Dual-Technique MIMO Antenna Design for IoT Millimeter-Wave Circular Polarization

This study presents an innovative dual approach design for a circularly polarized (CP) multiple-input multipleoutput (MIMO) antenna specifically tailored for millimeter-wave (mm-wave) IoT applications. The MIMO-CP antenna comprises four rectangular slatted radiators, a hexagonal nested neutralization line (HN-NL), and a circular segmented defected ground (CS-DG). The effective decoupling compact antenna dimensions are 30×30×0.508 mm³ (2.80λ₀× 2.80λ₀× 0.0457λ₀) while λ0 is the free space wavelength at 28 GHz. The integration of HNNL and CS-DG among the MIMO radiators facilitates a decoupling strategy that improves the axial ratio (AR) bandwidth (BW), and isolation. The antenna achieves a 3-dB ARBW from 27.21 to 32.83 GHz (20.67%), a mutual coupling (MC) of no more than -28 dB, a reflection coefficient of ≤ −10 dB from 25.12 to 34.5 GHz (30.96%), and a peak gain of 7.25 dBi at lower frequencies and 8.13 dBi at higher frequencies. The efficient MIMO characteristics of the compact, low-profile antenna provide them an attractive choice for IoT mm-wave applications.