The S-parameter retrieval and MG (Maxwell-Garnett) effective medium theory were employed to calculate the effective dielectric constant of composite medium containing ellipsoid nanoparticles. Two influential factors

including volume fraction and aspect ratio of ellipsoid

were considered to analyze the applicability of the two effective models. Results showed that S-parameter retrieval had better adaptability to changes in shape and volume fraction of doped nanoparticles. In the considered volume fractions and aspect ratios

the S-parameter retrieval was well applicable. However

the MG effective medium theory was easily affected by the volume fraction and aspect ratio. When the aspect ratio of ellipsoid was 2

3 or 4

the maximum volume fraction under applicable MG effective medium theory was 8%

4% or 2%. Therefore

as the ellipsoid becomes flattened

the applicable range of MG effective medium theory will continue to decrease.