A generalized Maxwell Garnett model for artificial composites formed of small bianisotropic particles arranged in three-dimensional arrays is developed. Explicit expressions for averaged dyadic constitutive parameters are given. The approach is suitable for the case of incomplete magnetoelectric coupling dyadics, since it leads to expressions which do not involve any inverses of these dyadics. Based on an analytical antenna model of single chiral particles, the averaged parameters can be easily evaluated. The theory is illustrated by numerical examples for uniaxial chiral structures. Reflection coefficients from an ideal conductor covered by uniaxial chiral slabs are calculated for different types of axially symmetric distributions of the inclusions. It is demonstrated that for different frequency ranges different geometries correspond to better reduction of reflection.