Modal Expansion Analysis, Inverse Design, and Experimental Verification of a Broadband High-Aperture Efficiency Circular Short Backfire Antenna Loaded with Anisotropic Impedance Surfaces

In this article, a broadband highly efficient circular short backfire antenna (SBFA) loaded with cylindrical anisotropic impedance surfaces (AISs) is proposed. An efficient modal expansion method (MEM) is developed to facilitate the analysis of the AIS-loaded SBFA with a finite-sized flange, which considerably reduces the computational resources as compared to commercial full-wave solvers. By combining the MEM with a multiobjective genetic algorithm, the geometrical dimensions of the antenna and the dispersive properties of the AIS are optimized through an inverse design strategy. As a proof-of-concept example, an S-band AIS-loaded SBFA with a broad bandwidth and high aperture efficiency is demonstrated, showing a good agreement between measured results and simulation predictions. An aperture efficiency of greater than 83% is experimentally achieved over a broad $S_{11} < -10$ dB bandwidth of 35.3%, with a peak aperture efficiency of about 100%. Moreover, the underlying operating principle of the antenna is revealed by the investigation of the main propagating modes in the SBFA. The extraordinary performance demonstrates that the proposed AIS-loaded SBFA represents a promising candidate for various wireless communication systems.