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A rectifying surface for energy harvesting with optimal RF‐to‐DC efficiency insensitive to polarisation collimation is presented based on metasurface and branch‐line coupler. The metasurface captures two orthogonal components of incident wave by two separate loads with high efficiency. A 90° branch‐line coupler is introduced to redistribute two polarisation‐dependent components into two invariant equipower outputs, aiming to preserve continuous impedance‐matching between metasurface and rectifiers for maximised conversion efficiency. The proposed rectifying surface has been fabricated and measured. The measured fluctuation ranges of capture and conversion efficiency are smaller than 2 and 0.5%, respectively, agreeing well with authors' prediction. They expect a wide range of applications to emerge from this novel concept in the future. [ABSTRACT FROM AUTHOR]

Diffractive antennas implement steerable beams based on reconfigurable diffractive devices such as Fresnel zone plates (FZPs). Compared with phased array systems, FZP antennas have concise architectures and simple beam‐steering mechanisms. In this Letter, the authors demonstrate an FZP‐based reconfigurable diffractive antenna with three degrees of freedom (3DoF), i.e. simultaneous reconfigurable steering angle, beamwidth and operating frequency. Such a highly reconfigurable antenna is implemented based on a single‐layer metasurface mounted with microwave varactors. The principle behind this 3DoF reconfiguration is the electrically induced transparency and opacity switched by different sets of binary voltages applied across the varactors. Experimental measurements validated the proposed approach. [ABSTRACT FROM AUTHOR]

Through‐wall imaging (TWI) is a challenging topic in the area of inverse scattering problem based microwave imaging. A TWI solution based on non‐linear inversion algorithms is experimentally investigated. Experiments are performed using a setup with the object surrounded by a closed wall. The inversion is based on a twofold subspace‐based optimisation method, and the results show that the location, shape, size, and dielectric constant of the object can be successfully retrieved from the measured scattering data. This is the first experimental demonstration of TWI of objects behind a closed wall using a non‐linear inversion algorithm. These results imply the potential of TWI for practical applications. [ABSTRACT FROM AUTHOR]