Research On Beamforming Of Transmit Arrary Based On Metamaterial

Intelligent driving methods such as assisted driving and automatic driving brings a booming development of opportunities for millimeter-wave(MMW)automotive radar.Compared with conventional image sensors,ultrasonic radars and infrared sensors,77 GHz millimeter wave automotive radar system performs well regardless of complex weather conditions such as night,heavy rain and fog.Considering the limitation of vehicle space,the automotive radar antenna is required to be lightweight,low profile,and low expense.However,millimeter wave radar is faced with problems such as large size,low gain,high expense and so on.The need for high-gain,beam steering,and wideangle beam antenna are extremely urgent due to the trend to autonomous driving progressing rapidly.Transmit array(TA)composed of a series of periodic subwavelength unit cells have recently caught the sight of researchers tremendously due to its high flexibility in beamforming functionalities and low cost.Compared with traditional reflect arrays and dielectric lenses,TA enjoy numerous advantages such as low profile,low cost,lightweight and easy manufacturing technique.Besides,contrary to RAs.TA do not suffer from feed blockage and have better tolerance to surface phase error.TA have been widely exploited for various fields,ranging from automotive radar,5G communication to tracking,imaging and so on.The chief contributions in this paper are as follows:Firstly,a metamaterial based transmission array cell,which operates at 77GHz and consists of a double layer of medium and three metal layers,is designed.The cell with a total thickness of 0.5mm is much thinner than other transmission cells in the same frequency band.By adjusting the size of the metal layer,the unit can achieve 0-360° phase coverage.In order to simplify the design,the phase shift range was quantified into 8 phase intervals,and the central phase of each interval was used to replace the interval.In addition,for the feed antenna of the transmission array antenna,a horn antenna with varying Angle covering 77GHz is used as the feed of the transmission antenna.The horn antenna effectively balances the relationship between horn length,aperture size and antenna gain to match the transmission array.After designing high performance transmission unit and feed antenna,the phase distribution of high gain pen beam is studied to solve the situation of vehicle-mounted radar antenna dealing with medium and long range detection point source.The point source detection in middle-range sector is studied by broadening pen beam by adjusting phase distribution.The phase distribution of sectors scanned by adjusting the phase is studied.