Novel Metasurface Lens-Based RF Sensor Structure for SAR Microwave Imaging of Layered Media

In this article, a novel low profile wideband highly directive gradient refractive index (GRIN) metasurface (MS) lens is designed to improve the gain of the X-band waveguide-based RF sensor system for the microwave imaging application. The proposed GRIN MS lens consists of several layers comprising the core layers at the centre and the impedance matching layers around both sides of the core layers. The core layers and the impedance matching layers of the proposed lens are based on a novel three-layer unit cell, wherein a single rectangular ring and two C-shaped strips are printed on both sides of the middle layer. The cross-sectional dimensions of the proposed unit cell varying across the lens aperture to realize the refractive index profile gradually varying from 1.5 at both edges to 7 at the centre. After designing the GRIN MS lens, an attractive microwave technique using a combination of piecewise synthetic aperture radar (PW-SAR) scheme and a time-domain algorithm for imaging of layered media is proposed. The use of a noniterative time-domain technique in the present situation basically helps to retrieve the electrical and physical properties of each layer, which are inherently required for the SAR algorithm to obtain a focused image of the target object buried in the layered media. The experimental results show that the integration of the proposed GRIN MS lens with the RF waveguide sensor improves the overall gain by the maximum value of 10.5 dB, thereby enhancing the spatial resolution of the target object in a layered media using the modified SAR imaging scheme.