In this paper, an eight-port millimeter-wave multiple-input-multiple-output (MIMO) antenna array operating at 28 GHz for vehicle to vehicle (V2V) communication is designed and developed. It consists of eight 2 × 2 half-mode substrate integrated waveguide (HMSIW) antenna arrays placed along the edges of a regular octagon. The 2 × 2 HMSIW antenna array is fed through a corporate feeding network that comprises of two-stage in-phase T-junction power divider. The designed antenna array has an overall volume of 0.72 \({\lambda }_{0}^{3}\) , where λ0 is the free-space wavelength at operating frequency of 28 GHz. It exhibits excellent peak realized gain (> 12.2 dBi) and high inter-port isolations (> 30 dB) among all the antenna elements without usage of any decoupling network. The MIMO performance of the proposed MIMO antenna array is evaluated in terms of envelope correlation coefficient (ECC) and diversity gain (DG). The performance parameters lie within their acceptable limits. The link budget analysis of the proposed MIMO antenna array is performed with the evaluation of path losses and link margins. To further enhance the gain and radiation characteristics, the 8-port MIMO antenna design, originally based on a 2 × 2 array, is extended to a 4 × 4 array configuration. High gain, high inter-port isolation and excellent radiation characteristics make the designed millimeter-wave MIMO antenna array a potential candidate for V2V communication system.
