Integrated Inverse Design of Antenna Superstrate for Radiation and Scattering Problems

A multi-functional integrated inverse-design method (MFI-IDM) of antenna superstrate is proposed to achieve the desired radiation pattern (DRP) and low radar cross section (RCS) of antenna by employing Born iterative-type methods. When the internal and external incident sources of the antenna are known, the proposed method first designs the corresponding far-field total and scattering fields of the superstrate based on physical definitions derived from the DRP and RCS requirements. Then, based on the designated domain of the antenna superstrate, its electromagnetic parameters can be reconstructed with the help of the inverse scattering algorithms. As a result, the antenna with inverse-designed superstrate can be modeled and finally meets the expected requirements of both high radiation performance and low scattering characteristics. Two schemes of multi-functional integrated design, involving single and multiple superstrates, are introduced. Additionally, a stepwise approximation strategy and a progressive design with multi-superstrate are proposed to avoid the divergence problem of inverse scattering algorithm. Based on two-dimensional numerical calculations, the inverse-designed dielectric-type superstrates are further extended to the applications of three-dimensional (3D) antennas. By dielectric equivalence, the designed dielectric-type superstrate was fabricated by using the 3D printing technology. The effectiveness of the proposed method is well validated by the full-wave simulations and measurements. When compared with other similar antennas, the final antenna with inverse-designed superstrate shows good electrical performance, achieving a measured 81° flat-topped beamwidth and 12.5 dB bistatic RCS reduction. Different from the traditional separated forward methods and single-objective inverse-design method, the proposed method efficiently completes the multi-functional inverse-design within a framework, thereby overcoming the limitations of traditional design method for multi-functional antennas.