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In this communication, we present a low-cost chipless radio frequency identification (RFID) tag with a high data capacity and a wide reading range based on time-domain scattering modulation. The proposed tag consists of a slotted square patch antenna with a switchable resistor and a mechanically driven slider etched with a barcode-like metallic wire array. Encoding is achieved by the presence and absence of the metallic wire on the slider, and tag identification is obtained by sequential bit reading. A special encoding strategy is applied to improve its insensitivity to the motion velocity of the slider. For a proof-of-concept demonstration, a prototype designed to operate at 2.1 GHz was fabricated and measured, and the experimental results verified the effectiveness. Compared with the methods based on time-domain reflectometry, spectral signature, and resonator-based sequential encoding, the proposed approach provides a substantially enhanced data capacity within a narrow spectrum without sacrificing its reading range and tag size, due to the design of nonresonant code cell. Such a mechanically triggered chipless RFID tag exhibits promising potentials in some practical applications, such as personal ID and credit cards. [ABSTRACT FROM AUTHOR]

Combining the advantages of the phase tunability provided by active frequency selective surfaces (FSSs) and the beam-steering scheme used in conventional 1-D Fresnel-zone-plate (FZP) antennas, we report in this communication a 2-D beam-steering FZP antenna that needs only 180° phase tunability. Compared with transmit arrays, while the substrate layers are reduced by a half, a phase compensation strategy is used to enhance antenna specifications. To verify the proposed approach, a radome implemented based on an active, reconfigurable FSS was designed, simulated, and experimentally implemented. With a simple three-layer structure, the implemented FZP antenna works within an ultrawide bandwidth ranging from 5 to 6.3 GHz, corresponding to a 21% relative bandwidth. With a gain up to 19.3 dBi, the scanning range reaches ±45° in both horizontal and vertical planes. This cost-effective, simple-structured antenna can be potentially used in diverse RF and microwave applications. [ABSTRACT FROM AUTHOR]

In this communication, we experimentally demonstrate a frequency- and beam-reconfigurable lens antenna based on an active second-order bandpass frequency-selective surface (FSS). The FSS lens is composed of three nonresonant metallic layers separated by two thin dielectric substrates. By integrating microwave varactors in FSS unit cells, the center frequency of this bandpass FSS can be tuned from 4.0 to 5.8 GHz by a direct-current (dc) bias voltage. Based on this wideband tunability, the phase-correction technique is used to implement a microwave Fresnel lens. The experimental results show that the proposed 1-D lens antenna can achieve frequency-reconfigurable beam steering within a 1 GHz bandwidth. With advantages of low cost and concise structure, the proposed reconfigurable lens antenna can be potentially used in a wide range of applications. [ABSTRACT FROM AUTHOR]

Spatial Kramers–Kronig (KK) relations have been recently proposed to achieve perfect absorption without using any gain elements or highly anisotropic materials. However, such perfect absorption is limited to the surface of an infinitely long planar slab in the Cartesian coordinate, and the cases of surfaces with bends or sharp corners are still challenging. In this article, we apply conformal transformation optics methods to design spatial KK media, which can achieve smooth perfect absorption both in cylindrical spaces and in polygonal spaces with sharp corners. Moreover, it is demonstrated that we can also control the scattering direction of the designed polygonal spatial KK media to realize invisibility. Our work opens new avenues for perfect absorption devices based on transformation optics and spatial KK relations. [ABSTRACT FROM AUTHOR]

In this paper, we present an analytical beam-forming approach capable of synthesizing differently shaped beams for circularly symmetric conformal apertures with axisymmetrical excitations. Closed form formulas of far-field radiation are mathematically derived in order to obtain rotationally symmetric radiation patterns for typical conformal apertures frequently used in satellite and flight vehicle applications, such as the cone-surfaced, truncated cone-surfaced, hybrid disc-cone and sphere-cone apertures. Based on these formulas, various shaped beams, including pencil, flat-topped and bimodal beams can be rapidly achieved by adjusting either the geometric parameters or the excitation distributions of the conformal apertures. The deterministic approach proposed in this paper provides an efficient method to synthesize specified beam shapes for the aforementioned conformal apertures. Collaborating with conventional optimization based beam forming approaches, the proposed approach can effectively shorten the time-consuming optimization in the beam forming of circularly symmetric conformal arrays, especially large conformal arrays. [ABSTRACT FROM PUBLISHER]

In this paper, the reconstruction of perfectly electric conductor (PEC) scatterers with transverse electric (TE) wave illumination is investigated using the continuous-type subspace-based optimization method (SOM). The PEC scatterers can be of arbitrary locations, shapes and quantities and no prior information about the scatterers is required in the reconstructions. Compared with the transverse magnetic (TM) counterpart, the TE case is not only mathematically more complex, but also numerically more demanding in the sense that the triangular basis is used to represent induced electric current. Moreover, under better mesh strategy and more strict objective function, numerical simulations for arbitrary PEC scatterers generate satisfactory results and are well robust against noise. The algorithm is also examined under the experimental scattering data and still obtains good reconstruction results. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a beam forming approach capable of synthesizing versatile, pre-specified beam shapes using concentric excitations satisfying multiple weighted sinc or Bessel function distribution. We show by both theoretical calculation and full wave simulation that by tuning different weights of a sinc or Bessel function distribution, not only radiation beams with pencil, flat-topped and bimodal shapes can be synthesized, but also the beam-width and the side lobe level can be independently adjusted. An example is provided to demonstrate how an isoflux beam aiming at a better coverage of the earth surface is synthesized, and how an optimized continuous distribution is properly discretized for a physical realization of a satellite aperture array antenna. The approach proposed in this paper can be applied to a wide range of applications that require performance optimization of concentric ring array antennas. [ABSTRACT FROM PUBLISHER]