Abstract
Recently, modern technologies of wireless communication have shown rapid progress, and because of these various applications in high frequencies there is a concern about effects on other electronic device and unexpected malfunctions. For these reasons, a microwave absorber in free space has become necessary for a safe electromagnetic wave environment.
In this report, we explain characteristic evaluations of a microwave absorber which is used in an electronic toll collection (ETC) device, fabricated by a composite of magnetic (Fe) and dielectric (TiO2) materials. It was evaluated by free-space method with horn antennas using a transverse electric wave, a transverse magnetic wave and a circularly polarized wave. The reflection loss in free space is -20 dB or more around a central frequency of 5.8 GHz at oblique-incident angles of up to 60°, which satisfy the necessary condition for ETC use in Japan, and using arrangement and changing structure, it also satisfies necessary condition for ETC use without a characteristic deterioration. In addition, we compare experimental results with calculation results of transmission line theory as well as EEM-FDM simulation results.
