There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Aspects of the subject disclosure may include, for example, a solid dielectric antenna having a non-uniform spatial distribution of relative permittivity.

System and dielectric antenna with non-uniform dielectric

The introduction of electromagnetic (EM) media with unique field manipulation properties, collectively labelled as metamaterials, has boosted the interest toward the design, the fabrication, and the testing of artificial materials whose features can be engineered according to the applicative requirements and user objectives. In this framework, the long-term promise of reconfigurable metamaterial theory (i.e., the possibility to change the EM response of a 2-D/3-D material arbitrarily and in real time) has given the designers an extremely wide number of new degrees of freedom for the synthesis of innovative adaptive systems. Moreover, successful experimental validations of reconfigurable metamaterials in the entire EM spectrum from microwaves to optical frequencies have further stimulated academic and industrial interests in developing devices with enhanced performances, efficiency, and robustness. Nevertheless, the exploitation of reconfigurable metamaterials in commercial devices is still an open problem with several challenges from both the theoretical and technological viewpoints. This paper is then aimed at reviewing the latest advances on reconfigurable metamaterial engineering from the methodological perspective also providing a comprehensive and balanced survey on latest concepts, current trends, and envisaged future developments on this active field of research.

Reconfigurable Electromagnetics Through Metamaterials—A Review

Transformation electromagnetics provides a practical approach to control electromagnetic fields at will. Based on this principle, novel devices such as the invisible cloak have been proposed. Here we examine the extension of this technique as applied to the design of flat devices in antenna systems. A method using discrete coordinate transformation is proposed, which allows the conversion of conventional devices with curved shapes into flat systems, while preserving their non-dispersive, isotropic, broadband, and lossless properties. Two specific design examples, a flat reflector and a flat lens embedded in free space, are presented. To avoid the loss and narrow bandwidth issues typically present in metamaterials, appropriate approximations and simplifications are introduced to make the all-dielectric devices, which are more practical to build. It is also shown that the discrete coordinate transformation is valid for both the E and H polarizations, as long as the local coordinates of the system remain near-orthogonal. Finite-Difference Time-Domain simulations are used to verify the performances of these designs, and show that the all-dielectric devices have similar broadband performances compared to the conventional ones, while possessing the advantages of flat profiles and small volumes.

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Discrete Coordinate Transformation for Designing All-Dielectric Flat Antennas

A conventional parabolic reflector is converted into a flat one based on the discrete coordinate transformation. Instead of general beam-steering techniques, such as off-axis feeding, tilting the feed/reflector, or utilizing phase shift, we show an alternative way to manipulate the reflected emission through tuning transformed dielectrics. The proposed design, only including the conventional dielectric components, has a merit of keeping the flat profile of a compact reflector system while possessing the ability to steer the radiation beams in a wide frequency band.

Wideband Beam-Steerable Flat Reflectors via Transformation Optics

In this paper, the properties of cylindrical high permittivity dielectric particles are studied. A design for broadband reduction of the scattering signature of metallic objects is proposed by implementing simplified ground-plane cloaking schemes. The devices are functional in the presence of a ground plane as well as in free space ranging from 4 GHz to 10 GHz. The required dielectric map for the cloak is achieved by means of manipulating the dimensions of the periodically distributed dielectric cylinders embedded in a host medium with a permittivity close to one. The scattering reduction effects are verified through simulation results. The proposed all dielectric cloaks are advantageous over other schemes due to their non-dispersive nature, the broad bandwidth, the low loss, and the ease of fabrication.

A broadband simplified free space cloak realized by nonmagnetic dielectric cylinders

Differential filter based on artificial surface plasmon

The gain of leaky-wave antennas typically has a frequency dependence, since at different frequencies use different amount of the available aperture. The frequencies variations of the gain are more significant when the bandwidth of operation is wider. Here, we propose a leaky-wave antenna in groove gap-waveguide technology with glide-symmetric leaky pins to improve the gain flatness and scanning angle. To validate this technique, one antenna is designed following this technique. Its realized gain is improved more than 3.0 dB in the frequency band from 8.5 GHz to 14.5 GHz. The 3-dB realized gain bandwidth is enhanced from 4 GHz (36%) to 6.2 GHz (55%), with a enhanced scanning angle from 18.0° to 32.5°.

Wenxuan Tang

Papers

Discrete Coordinate Transformation for Designing All-Dielectric Flat Antennas

Wideband Beam-Steerable Flat Reflectors via Transformation Optics

A broadband simplified free space cloak realized by nonmagnetic dielectric cylinders

Differential filter based on artificial surface plasmon

On the Enhancement of Scanning and Gain Flatness of Leaky-Wave Gap-Waveguide Antennas with Glide Symmetry