Microwave Absorbing Properties of Magnetic Composite Sheets for Oblique Incidence Angles

Single-layered magnetic microwave absorbers are designed for the achievement of low reflection coefficient over wide incidence angles at intelligent transport system (ITS) frequency (5.9 GHz). For the acquirement of microwave absorbers with a matching frequency of 5.9 GHz, three kinds of magnetic composite sheets were fabricated whose filler material is iron particles, TiCo- and RuCo-substituted M-hexaferrite particles. On the basis of transmission line theory, reflection loss has been calculated with variation of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarization. The minimum reflection loss (less than -20 dB) is predicted at 6 GHz for the three specimens with a different matching thickness. The smallest matching thickness is determined in the composite of iron particles (~2 mm) due to its high magnetic permeability and dielectric permittivity as compared with other ferrite composites (4 mm and 3 mm for TiCo- and RuCo-substituted M-hexaferrites, respectively). At this matching thickness of the magnetic composites, a low value of reflection loss (less than -20 dB) is predicted for wide incidence angles for TM polarization. In particular, Brewster angle (θ_B) is observed for TM polarization with no wave reflection. On the while, Brewster angle is not observed for TE polarization, resulting in higher reflection loss relative to TM polarization for oblique incidence.