  We present an analytical model which permits the calculation of effective
material parameters for planar metamaterials consisting of arbitrary unit cells
(metaatoms) formed by a set of straight wire sections of potentially different
shape. The model takes advantage of resonant electric dipole oscillations in
the wires and their mutual coupling. The pertinent form of the metaatom
determines the actual coupling features. This procedure represents a kind of
building block model for quite different metaatoms. Based on the parameters
describing the individual dipole oscillations and their mutual coupling the
entire effective metamaterial tensor can be determined. By knowing these
parameters for a certain metaatom it can be systematically modified to create
the desired features. Performing such modifications effective material
properties as well as the far field intensities remain predictable. As an
example the model is applied to reveal the occurrence of optical activity if
the split ring resonator metaatom is modified to L- or S-shaped metaatoms.
