| With the large-scale use of automotive radar,the safety performance of the car has been greatly improved,and the probability of car collision accidents is greatly reduced.As an important tool for radiating and receiving electromagnetic signals,the millimeter wave antenna which be used in automotive radar will directly affect the detection effect of automotive radars.At present,the frequency of most automotive anti-collision radars in the world is mainly concentrated in 24 GHz and 77 GHz frequency bands.24 GHz automotive anti-collision radar is mainly used for short-range target detection,while 77 GHz automotive anti-collision radar can be used for both short-range and long-range target detection.And most studies of automotive radar antenna are focusing on micro-strip array antenna.Although the array antenna can provide higher gain,there are also problems such as large antenna size,complicated structure,difficulty in integration,and narrow operating bandwidth.When using automotive radar to detect obstacles at different distances,it is not the only indicator that the antenna has higher gain.Therefore,the millimeter wave antenna which has wider band,smaller size and simpler structure can be widely used for automotive anti-collision radar system as well as the performance of radar also meet requirement.In order to satisfy the demand of short-distance and large-angle targets detection in automobile anti-collision radar systems,a wideband and high front to back ratio substrate integrated waveguide H-plane is designed in this paper at first.In order to solve the problems of narrow bandwidth and low gain of the traditional SIW horn antenna,the antenna performance is improved by loading the dielectric structure at the antenna aperture surface.Then the effects of dielectric structure of different shapes and sizes on antenna performance are analyzed.The impedance matching between the horn aperture and free space is improved by loading the metal patch structure on the upper and lower surfaces,and the influence of metal patch size and position on the impedance bandwidth of the antenna is analyzed.At next,a wideband SIW H-plane horn antenna is designed.This antenna can working from 21.7 to28.4 GHz,and the max gain can reach 11.25dB.Compared with the tradition antenna,the side lobe level and the back lobe level of this antenna are obviously suppressed.This antenna has a wide beam width which can reduce the blind spot range during detection.Secondly,a transmission metasurface unit cell is composed of four metallic layers and three intermediate dielectric layers.Each metallic layers contains a square ring outside and a ring inside.The transmission phase of this unit can cover the entire scope 0 to 360 degree by changing the inner and outer radius of the ring.And now the transmission efficient of transmission unit cell can always greater than 70%.If these transmission cell which its phase following the parabolic profile are arranged a 9×9 scale metasurface,the transmission electromagnetic waves will cause convergence when it normal incidence.At the moment,the size of this metasurface is only 14.4×14.4×4.5mm~3.Finally,in order to satisfy the demand of long-distance target detection in automobile anti-collision radar systems,a small and high-gain lens antenna is designed in this paper.A patch antenna is placed at the focal point of the metasurface as a feed source.The size of radiation patch is only 1.3×0.96mm~2,and the resonant frequency of this patch antenna is in78.3 GHz.The lens antenna is constituted by patch antenna and metasurface.The quasi spherical wave emitted by the source was transformed plane wave,and the gain of this lens antenna is significantly improved.The working frequency range of this antenna is 75.9-81.6GHz,and antenna gain is greater than 17.5 dB over most frequency ranges.The maximum gain can reach 18.25dB.Compared with other micro-strip array antenna,the half power beam width angle of this antenna is about 15 degree in each direction,and it's better for automotive radar to reduce blind spot range.The millimeter wave antenna designed in this paper not only has a higher gain,but also has other advantages of wider beam width angle,wider frequency band,smaller size,simpler structure,easier processing and integration.This paper provides a new idea for the selection and design of automotive anti-collision radar antennas. |
PDF Full Text Request