Wideband Narrow-Beam 16-Element Two-Port MIMO Array Antenna With High Isolation for Automotive Radar and 5G Millimeter Wave Applications

An eight-element linear array antenna is designed to provide a narrow beam, wide bandwidth, and high gain for compact electronic devices while mitigating propagation losses. The design is extended to a two-port MIMO array to enhance channel capacity and reduce RF chain complexity, and can be further scaled to an N-port configuration. A parallel feeding network ensures uniform power distribution. Wideband impedance matching and self-decoupling are achieved by optimizing the ground plane using characteristic mode theory (CMT). Both array and MIMO antennas are fabricated and measured, validating the simulations. The array antenna demonstrates good matching from 20.7 to 42.4 GHz and exhibits circular polarization (CP) with 3 dB axial ratio over 37.5-40.5 GHz atθE = 20∘. The MIMO antenna shows similar matching and CP performance over 37.5-39 GHz. Both achieve narrow beamwidths of 16.5∘-7.5∘ in YZ-plane (H-plane) and fan-shaped beams in the XZ-plane (E-plane), with sidelobe levels between -7 and -16 dB. The MIMO antenna meets all diversity metrics, achieving isolation better than 30.5 dB. Further, the MIMO antenna performance is verified with the frequency-modulated wave and beam-steering radar architecture for automotive radar applications.