Effects of incident directions on reflection coefficients of pyramidal electromagnetic wave absorber

The pyramidal wave absorbers are widely used in anechoic chambers which frequently used for EMC or antenna measurements. It is important to know reflection characteristics of pyramidal absorbers to improve the performance of anechoic chambers. It is known that diffracted or scattered waves are excited when the pyramidal wave absorber is irradiated by a plane wave, thus to know the characteristics of diffracted wave from pyramidal absorbers is also important. In this paper, The diffraction coefficients of pyramidal wave absorbers are calculated by using FDTD method. The higher mode diffraction coefficients are extracted by discrete Fourier transform. By using the extracted coefficients, the effects of incident directions to pyramidal wave absorber on its reflection coefficients and an SVSWR simulation are presented. The design and further analysis for pyramidal wave absorbers including diffraction effects are left for further study.