Abstract

AbstractFor EMI protection in high‐frequency regions beyond 1 GHz, composite materials made of rubber filled with soft magnetic metal powders have been used. With such materials, resonances in metal casings for amplifiers and coupling between transmission lines can be suppressed. In this paper, to provide a low‐pass‐type filter characteristic to the transmission line on a printed circuit board, a method is studied for covering a microstrip line (MSL) with such a composite material sheet and the necessary analysis is carried out. First, the propagation characteristics and the characteristic impedance of the MSL are derived numerically. Based on such information, the transmission and reflection characteristics as a filter are evaluated. Since the product of the complex relative permeability and the complex relative permittivity of the composite material sheet is larger than that of the substrate in this case, the quasi‐TEM mode approximation does not hold. Hence, the frequency domain finite‐difference (FDFD) method taking into account all electromagnetic field components is used for the analysis of the MSL. In the experiment, S11 and S21 of the MSL with its section coated with a composite material sheet are measured and compared with the analysis results. The computed results exhibit the same tendency as the measured data. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(11): 66–74, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10100

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