| With the widespread application of automotive radar systems,the safety performance of automobiles has been guaranteed,and the accident rate has been significantly reduced.As an important part of the automotive radar system,the antenna is responsible for the transmission and reception of electromagnetic waves.The performance of the antenna directly affects the detection capability of the radar system.Currently widely used automotive radar antennas include lidar,ultrasonic radar,millimeter-wave radar and so on.Among them,millimeter-wave radar has gradually become the mainstream of vehicle radar antennas due to its small size,high resolution and long detection range.Nowadays,the frequency bands of automotive radar antennas are mainly concentrated in 24 GHz and 77 GHz.The 24 GHz radar develops earlier and is mainly used in short-range mode.The 77 GHz radar develops late,but with its higher frequency characteristics,the antenna has a smaller size and higher detection accuracy.It can be used in short-range,medium-range and long-range modes.Therefore,77 GHz radar has better research value and broader application scenarios.The mainstream forms of automotive radar antennas include microstrip array antennas and planar lens antennas.Microstrip array antennas can synthesize high-gain beams through arrays,and have the characteristics of low profile.However,there are problems with complex feed networks,large transmission losses of microstrip lines,and narrow bandwidth.Planar lens antennas use the principle of optical focusing to generate ultra-high gain beams,but they also have problems with complex structure and large size.Focusing on the above-mentioned antenna structures and existing problems,this paper has launched the following work:According to the needs of automotive radar systems for detection in short distances and large ranges,two 1×10 microstrip linear arrays have been designed.The first microstrip linear array uses Chebyshev method to design the element current,and realizes the current distribution by adjusting the width of the array element to suppress the sidelobe level.The frequency band of the antenna is76.21GHz-77.97 GHz,the maximum gain is 16.14 d B,the sidelobe level is-19.77 d B,the 3d B beamwidth on the E plane is 9.7°,and the 3d B beamwidth on the H plane is 78°.Then,the linear array is formed into a 10×10 planar array to increase the gain of the antenna.The second microstrip linear array is improved on the basis of the first array.By adding a dielectric layer,a rectangular slotted gap is loaded between the two dielectric layers to expand the bandwidth.In addition,some metal through holes are loaded around the rectangular slot to form an SIW resonant cavity to suppress surface wave loss and improve the efficiency of the antenna.Finally,this new antenna achieves a bandwidth of 6GHz(74GHz-80GHz),a maximum gain of 15.8d B,and a sidelobe level of-15 d B.According to the needs of automotive radar systems for detection in medium and long distances,a planar lens antenna based on double-layer phase shift metasurfaces is designed.The designed lens unit adopts a double-layer patch structure,which can achieve a high transmission magnitude above0.9 on the basis of 3-bit transmission phases.In addition,a broad Band variable-angle horn antenna with a low sidelobe level is designed as a source feed.The designed lens antenna has a maximum gain of 32.4d B,a-1d B gain bandwidth of 9.15%,a sidelobe level of-20 d B,and a beam scanning angle of ±30°.The high gain and narrow beam characteristics of the antenna make it suitable for high-resolution detection at ultra-long distances.The good beam scanning characteristic can effectively reduce the detection blind area of the radar system. |
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