A High-Isolation High-Gain MIMO Millimeter-Wave Antenna Array

In this study, a high-isolation and high-gain multiple-input multiple-output (MIMO) antenna array operating at 77 GHz is proposed. It consists of two columns of transmitting (TX) sawtooth linear antenna arrays and two rows of receiving (RX) sawtooth linear antenna arrays with a rectangle ring layout. Each TX and RX linear antenna array contains 12 and 24 antenna units, respectively. The TX and RX antenna units adopt the same topology of a metal cavity fed by a substrate-integrated waveguide (SIW) slot. We introduce several $3\times $ 3 metal pin arrays to increase the gain and isolation of the TX and RX antennas. The metal pin arrays surround the four edges of the metal cavity on the top surface, and adjacent metal cavities share two metal pin arrays. Simulated results reveal that the antenna units exhibit a broad bandwidth of 75.3–81 GHz with S 11 less than −15 dB. The boresight gains of the TX and RX antenna units surpass 12 dBi, and the isolation is around 42 dB at 75–81 GHz. To verify the antenna’s performance, four WR 12 waveguide ports are used to excite two adjacent TX and two adjacent RX antenna units. The measured voltage standing wave ratios (VSWRs) of the TX and RX antenna units are less than 2 at 75–81 GHz, and the measured isolation between adjacent antenna units is more than 37 dB. Moreover, the measured boresight gains and radiation efficiencies of the TX and RX antenna units are 10–11 dBi and 60%–70%, respectively. This high-gain and high-isolation MIMO antenna array can be used for millimeter-wave (MMW) automotive radar.