Study of Coupling on Parallel Microstrip Lines Due to Magnetic-Loaded Absorber Sheet

Coupling effect of magnetic-loaded absorbing materials on parallel microstrip lines was investigated numerically and experimentally. A microstrip circuits with two 50 $\Omega$ parallel lines with different distances between the lines were used to experimentally evaluate coupling effect and the same configuration was modeled and evaluated with finite-element method numerical program. Results showed that absorber sheets, placed over microstrip lines significantly increase coupling at frequencies up to few GHz, depending on the absorber geometry. At higher frequencies, absorber sheets decrease coupling mostly due to dielectric and/or magnetic losses. Both numerical and experimental study show that permittivity has greater effect on coupling than permeability, which suggests that coupling is primarily due to electric field and not magnetic field. Further, we analyzed the geometry effects on the coupling, where we studied influence of length, thickness and different positions of absorber sheet on microstrip and also examined the effect of air gap between microstrip lines and absorber sheet.