The anisotropic conductivity of unidirectional carbon fibre reinforced polymer laminates and its effect on microstrip antennas

Carbon fibre reinforced plastic (CFRP) is being used increasingly in vehicle structures because of its relatively high stiffness and strength but light weight. Understanding then exploiting the electromagnetic behaviour of CFRP would enhance further some aspects of vehicle performance. The conductivity of unidirectional (UD) CFRP laminates was measured over the X-band. It was found that UD CFRP acts as a conductive surface when the E-field is parallel, and a lossy dielectric when the E-field is perpendicular, to the orientation of the fibres. Microstrip antennas were produced with quasi isotropic CFRP ground planes and showed resonant frequency of the antenna was 10 % higher when the microstrip antenna was mounted parallel to the first ply fibre orientation.