Design Features of Antenna Arrays of Automotive Radars Based on Transmitting and Receiving Multi-Element Modules

Introduction. Modern vehicles are equipped with radars, which serve as the main sensors of driver assistance systems detecting objects in all weather conditions. Antenna arrays (AA) are the most common type of radar antennas. The coefficient of mutual coupling between adjacent antenna channels has a significant effect on the formed radiation pattern (RP) of an AA. This aspect is important for achieving the required values of gain and side-lobe level (SLL). This article analyses the effect of the proposed design solutions on the main parameters of an automotive radar AA, in particular, on the mutual coupling coefficient between the channels and the SLL of the DP.
Aim. To develop an optimal approach to constructing an AA topology in terms of reducing the level of mutual influence of adjacent array channels and obtaining a DP with specified characteristics.
Materials and methods. To achieve the required parameters of the designed AA topology, the coplanar and microstrip lines were calculated using the finite element method and shield models.
Results. An electrodynamic modeling of a millimetre-wave AA was carried out. The effect of coplanar transmission lines on the RP was shown. The features of applying shielding elements in the AA structure were investigated. Antenna patterns were obtained for both an AA designed based on coplanar transmission lines and that based on the use of shields. The conducted comparative analysis determined the parameters of the substrate optimal for achieving a better level of decoupling between adjacent antenna channels. The values of AA RP obtained during modeling were presented.
Conclusion. The use of coplanar transmission lines can significantly reduce the SLL of the DP in the elevation plane. When implementing the module structure of an array (using of sub-arrays), the power dividers are realized. In this case, instead of coplanar lines, it is advisable to use specific microstrip constructions covered with shielding surfaces. In this case, the formation of a given amplitude-phase distribution over aperture is possible. A comparative analysis of the AA topologies with different substrates was carried out with the purpose of achieving improved decoupling. The obtained values of the coefficient of mutual influence of adjacent array channels correspond to those of modern AA of automotive radars. The methods of reducing the parasitic radiation of transmission lines were considered. The AA RP obtained via electrodynamic modeling were presented. The use of a thin substrate with a higher dielectric constant makes it possible to improve the AA characteristics.

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