  In this paper, we propose a new approach for realizing antireflection coating
using metamaterials. In this approach, a subwavelength array of metallic
pillars (with square cross-section) is used for implementing antireflection
coating. The effective impedance of the array can be duly adjusted by the size
and distance of pillars. Therefore, we design the effective impedance of the
antireflection coating to be the geometrical mean of the upper and lower
mediums impedance and we choose its height to be a quarter of operating
wavelength. Consequently, the reflection vanishes at the desired frequency and
fractional bandwidth of 56% is achieved with a criterion of 10% reflectance
(the refractive index of the substrate is assumed to be 4). The proposed
structure is symmetric in both directions. So, it is not sensitive to the
polarization of the incident wave at normal incidence. Furthermore, we show
that using the multilayer Chebyshev matching transformer of transmission line
theory increases the bandwidth of the antireflection up to 107% at the expense
of pass-band ripples. This structure can be used from very low frequencies up
to infrared regime by appropriate scaling.
