  We investigate the response of terahertz metamaterials made of split-ring
resonators depending on the unit cell density. It is shown that the fundamental
resonance has its highest Q factor for a period of one-third the resonance
wavelength. Increasing or decreasing the period from that optimal period
reduces the Q factor. All observations are explained by understanding radiative
coupling as the dominant loss mechanism at low densities, whereas the strong
inter SRR coupling enhances non-radiative losses at high densities. Our results
allow designing metamaterials with adjustable Q factors and possibly suggesting
that an optimal package density exists to induce the strongest dispersion.
