The Effect of Ply Orientation on the Performance of Antennas in or on Carbon Fiber Composites

In this paper, the anisotropic conductivity effect of quasiisotropic carbon fiber laminates on conformal load-bearing antenna structures (CLAS) is presented. The conductivity of a quasi-isotropic IM7/977-3 CFRP laminate is measured using waveguide techniques. The results show that orientation of the surface ply relative to the polarization of the incident E-field has a major influence on the reflectivity. This difference is attributed to the fact that carbon fibres oriented parallel to the E-field plies behave as good conductors, while off-axis plies present as lossy dielectric layers with a finite conductivity. This anisotropic behavior of the ply layers is shown to have a distinctive influence on the operation of both microstrip patch and slot antennas.