  We present an effective-medium model for calculating the frequency-dependent
effective permittivity $\epsilon(\omega)$ and permeability $\mu(\omega)$ of
metamaterial composites containing spherical particles with arbitrary
permittivity and permeability. The model is derived from the zero-scattering
condition within the dipole approximation, but does not invoke any additional
long-wavelength approximations. As a result, it captures the effects of spatial
dispersion and predicts a finite effective refractive index and antiresonances
in $\epsilon(\omega)$ and $\mu(\omega)$, in agreement with numerical
finite-element calculations.
