A fundamental study of a thin lambda/4 wave absorber using FSS technology

The lambda/4 wave absorber is expected to be useful for indoor wireless LAN because of its simple structure and ease of design. However, this type of wave absorber has the deficiency that the thickness cannot be less than 1/4 of the wavelength within the spacer used. In this paper, an FSS (Frequency Selective Surface) is inserted in tandem with a resistive film as an absorbing film in the spacer section of the lambda/4 wave absorber. By varying the phase within the spacer, thickness reduction of the absorber is attempted. In this case, it is necessary to understand the impedance of the FSS at the design frequency. In this paper, the impedance is first derived by the FDTD method. Substituting this result into an electric equivalent circuit, the insertion position of the FSS and the surface resistivity of the resistive film maximizing the absorbing characteristic are determined. A thin lambda/4 wave absorber of this type is designed and fabricated and the absorption is measured. It is confirmed that a lambda/4 wave absorber can be realized with approximately half the conventional thickness. Basic data on the frequency characteristics and angular dependence of this type of absorber can be obtained. (C) 2004 Wiley Periodicals, Inc.