Optimization of C-like sandwich wall structure for high microwave transmission

A multilayered structure of five planar slabs ((Glass epoxy/PU Foam/Vacuum/PU Foam/Glass epoxy) was investigated for broadband microwave propagation. In this study, theoretical calculations of the transmittance, reflectance and absorbance characteristics of the multilayer structure were carried out using the ABCD transfer matrix method, and numerical calculations were obtained using the COMSOL Multiphysics simulation software. The propagation characteristics were investigated as a function of frequency up to the Ka-band and versus angle of incidence ranging from normal to grazing incidence. The results of the theory and simulation were in excellent agreement. The average transmittance for unpolarized or circularly polarized wave was 97% over the S to the K bands, whereas up to 86% transmission was observed at the end of the Ka-band. Higher than 95% transmission of incident waves with frequency 10 GHz was observed over a wide range of angles of incidence up to $70°$, after which the transmittance decreased sharply to zero at a grazing incidence (${\theta }_1=90°$). The results revealed that the absorbance is negligibly small and the incident energy was either transmitted or reflected. The reflectance for both TE and TM wave modes increased appreciably in the angular range $75°\le {\theta }_1\le 90°$ and approached 100% at grazing incidence. The curves of the reflectance versus angle of incidence for representative frequencies in the S and X bands revealed a Brewster-like effect for the TM wave mode, while the reflectance of the TE mode varied monotonically, without showing a minimum characteristic of a Brewster-like reflectionless condition.