Abstract: A broadband high-isolation and low-cost millimeter-wave antenna array unit, which is suitable for engineering applications,is proposed in this paper. The proposed antenna array unit combined the advantages of both the planar substrate integrated waveguide (SIW) antenna and the metal horn antenna, taking the cavity-baked SIW patch antenna as the primary feed of simplified horn antenna, introducing several resonance structures to improve the bandwidth performance. The advantages of the proposed antenna include fabricated-friendly, low-cost in fabrication, and the high isolation between different units. Both simulated and measured results show that the antenna array unit has good matching and radiation characteristics, isolation between different units is better than -30dB during the working frequency band between 77GHz to 84GHz, making the antenna array unit a potential choice for millimeter-wave applications.