Abstract: Based on the X-type metal structure,a unit cell of composite left/righthanded transmission line(CRLH-TL)with ultra-wideband is proposed.The unit cell is composed of a dielectric-slab and the X-type metal structures reverse symmetrically set on both sides of the slab.The distribution parameters circuit theory is used to analyze the cause of the left and right-handed properties of the material in general, and the effective parametric extraction method is used to extract the relative permittivity and relative magnetic permeability from the Sparameters of the structural unit.Furthermore,the refractive index is also computed to validate the transmission characteristics of the CRLH-TL.The Simulation results demonstrate that the structural units could give rise to both right-handed and left-handed pass-band in the case of an electromagnetic wave paralleled incidents on the dielectric-slab.It also shows ultra wideband characteristics in the S-frequency band;meanwhile,it could get zero refractive index at other frequency points.A positive-zero-negative composite medium material is constructed.