Modified metasurface Alvarez lens based on the phase compensation in a microwave band

Alvarez lenses, a kind of passive zoom lenses with reconfigurable focus, have been widely applied in optics but very few at lower frequencies such as in a microwave band, where the phase approximation for Alvarez lenses becomes inaccurate. In this article, we propose a design of a modified Alvarez lens with phase compensation for microwave, which consists of a pair of transmissive metasurfaces with high efficiency. The proposed metasurface consists of miniaturized units with the capability of full 2π phase modulation. We further analyze the phase distribution principle of the Alvarez lens and proposed a phase compensation scheme. The simulation results confirm that the proposed modified Alvarez lens has a very good dynamic focal length with theoretical expectation and can be continuously adjusted from 100 to 200 mm.