Flat Lens as a Collimator for Tapered Anechoic Chamber

The tapered anechoic chamber is an effective measuring facility in the frequency range from 0.1 to 1 GHz. Collimator lens is used to create quasi-plane wave in such chambers. In this work we consider using a flat lens as a collimator. Refraction in this lens is achieved by refraction coefficient that gradually changes from the center to the edge of the lens. Flat lens was theoretically considered in literature and it is known as Zaitsev lens. Practical realization of such lens is achieved by 3D-printing a periodic structure with cell that has square holes of different size and hence different effective permittivity. During the work we proposed a formula for calculating effective permittivity, designed and printed the model of flat lens. Experimental investigations of near field behind the lens showed that variations of the phase do not exceed $\pi / 8$.