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In this letter, we propose and experimentally demonstrate a space‐fed beamforming approach capable of steering beams up to ±70° with a focal ratio (F/D) reduced to 0.27 and a scan loss remained 4 dB. It is implemented based on an mmWave phase reconfigurable metasurface, and an unconventional array‐fed architecture. By doing so, while the total profile of conventional space‐fed phased arrays can be significantly reduced, specifications such as scan range and scan loss can be simultaneously improved. Compared with conventional phased array systems, such specifications are unique, and can be used to realize low‐profile, cost‐effective, space‐fed phased arrays requiring ultrawide coverages at mmWave frequencies. [ABSTRACT FROM AUTHOR]

Spatial Kramers–Kronig (KK) medium provides a new platform to achieve omnidirectionally reflectionless absorption without using any gain elements. However, impedance‐matched spatial KK media realized in previous experiments generally have flat geometries with large transverse dimensions. Realizing finite spatial KK absorbers in free space background is important for many practical applications but has not been demonstrated experimentally thus far. Here, the concept of spatial KK relation to cylindrical coordinates is extended and a double‐resonance space‐frequency KK permittivity profile is implemented in a circular geometry. Omnidirectional impedance matching to free space is achieved by truncating the spatial KK absorber at the boundary where the relative permittivity is unity. For the experimental verification, a two‐dimensional 6.6‐wavelength‐diameter doughnut‐shaped anechoic chamber is implemented using the designed spatial KK medium. The measured electric field distributions and experimental imaging confirm the omnidirectionally reflectionless property, demonstrating that this miniaturized anechoic chamber is suitable for electrically small scatterer measurements and imaging. The proposed finite spatial KK absorber and fabricated miniaturized anechoic chamber show great promises for electromagnetic shielding and compatibility. [ABSTRACT FROM AUTHOR]

We investigate a non-Foster element implemented with a radio-frequency operational amplifier theoretically and experimentally, showing that its full-range frequency response exhibits an inverted Lorentzian resonance, and thus a high-frequency non-Foster response can be observed on the right side of the resonance region. This can be used to overcome the technical difficulty in achieving high-frequency non-Foster elements. [ABSTRACT FROM AUTHOR]

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]

In this article, we propose a design and on-board measuring approach for the realization of micro-sized differential antennas for the 2.4-GHz mobile payment (MP) applications. Exampled by a complete realization of a 3 × 11 mm-sized differential antenna driven by a commercial 2.4-GHz transceiver integrated inside a 15 × 11 mm-sized micro-SD card, such design and testing approach is described in detail. The experimental measurements of the micro-sized antenna show that the impedance of the designed micro-sized differential antenna well matches the complex impedance of the transceiver, and, therefore, ensure the stability of the radio frequency performance required by the MP applications. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1419-1422, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25957 [ABSTRACT FROM AUTHOR]