Modeling Pyramidal Absorbers Using the Fourier Modal Method and the Mode Matching Technique

The problem of plane wave diffraction from the periodic structure of an infinite PEC wall lined with pyramidal absorbers is considered. A hybrid method based on the R-matrix Fourier modal method (RFMM) and the mode matching (MM) of fields is used for the efficient and robust analysis of this class of absorbers. The hybrid method benefits from the discrete spectrum of the periodic structure in transverse directions and consequently avoids spatial discretization along the periodicity axes. This leads to considerable reduction in the number of unknown coefficients. Furthermore, the method is capable of considering dispersive and inhomogeneous materials which are frequently used in the absorber industry. Several examples are outlined, simulated, and measured to show the efficiency and accuracy of the method. The versatility and flexibility of the hybrid RFMM-MM technique makes it suitable for the optimal design of pyramidal absorbers to achieve further improvements in their performances.