Comment on "Superwide-band negative refraction of a symmetrical E-shaped metamaterial with two electromagnetic resonances"

The metamaterial presented by Yan [Phys. Rev. E 77, 056604 (2008)] is claimed to exhibit a superwide band of negative refraction. However, a retrieval procedure of the refractive index including the phase advance of a propagating plane wave shows that the material provides two distinct narrow bands with a negative refractive index instead of a single superwide band and thus the central claim of the paper is incorrect.