title: Comment on "Superwide-band negative refraction of a symmetrical E-shaped metamaterial with two electromagnetic resonances".
abstract: The superwide-band negative refraction of the symmetrical E-shaped structure designed by Yan [Phys. Rev. E 77, 056604 (2008)] may not exist. While we accepted the validity of scattering parameter simulations completely, the process of retrieving material parameters could not be justified.
authors.affiliation: The College of Science, Air Force University of Engineering, Xi'an 710051, People's Republic of China. guchao123abc@sina.com
authors.forename: Chao
authors.initials: C
authors.lastname: Gu
authors.forename: Zhibing
authors.initials: Z
authors.lastname: Pei
authors.forename: Shaobo
authors.initials: S
authors.lastname: Qu
authors.forename: Jiafu
authors.initials: J
authors.lastname: Wang
authors.forename: Hua
authors.initials: H
authors.lastname: Ma
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Xu