Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. This class of micro- and nano-structured artificial media have attracted great interest during the past 15 years and yielded ground-breaking electromagnetic and photonic phenomena. However, the high losses and strong dispersion associated with the resonant responses and the use of metallic structures, as well as the difficulty in fabricating the micro- and nanoscale 3D structures, have hindered practical applications of metamaterials. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response (e.g. scattering amplitude, phase, and polarization), mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

A review of metasurfaces: physics and applications.

Optical metasurfaces have developed as a breakthrough concept for advanced wave-front engineering enabled by subwavelength resonant nanostructures. However, reflection and/or absorption losses as well as low polarization-conversion efficiencies pose a fundamental obstacle for achieving high transmission efficiencies that are required for practical applications. Here, for the first time to our knowledge, highly efficient all-dielectric metasurfaces are demonstrated for NIR frequencies using arrays of silicon nanodisks as metaatoms. The main features of Huygens' sources are employed, namely, spectrally overlapping crossed electric and magnetic dipole resonances of equal strength, to demonstrate Huygens' surfaces with full transmission-phase coverage of 360° and near-unity transmission. Full-phase coverage combined with high efficiency in transmission are experimentally confirmed. Based on these key properties, all-dielectric Huygens' metasurfaces can become a new paradigm for flat optical devices, including beam-steering, beam-shaping, and focusing, as well as holography and dispersion control.

High-Efficiency Dielectric Huygens’ Surfaces

Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response, mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

A review of metasurfaces: physics and applications

Linearly and circularly polarized conformal strip-fed dielectric resonator antennas (DRAs) are studied in this article. In the latter case, a parasitic patch is used to excite a nearly degenerate mode. The hemispherical DRA, excited in its fundamental broadside TE111 mode, is used for the demonstration. In the analysis, the mode-matching method is used to obtain the Green's functions, whereas the method of moments is used to solve for the unknown strip currents. In order to solve the singularity problem of the Green's functions, a recurrence technique is used to evaluate the impedance integrals. This greatly increases the numerical efficiency. Measurements were carried out to verify the calculations, with good results.


Keywords:

circularly polarized antenna;
dielectric antennas;
mode-matching methods;
moment methods;
parasitic antennas;
resonance

Dielectric Resonator Antennas

Open dielectric resonators (DRs) offer attractive features as antenna elements. These include their small size, mechanical simplicity, high radiation efficiency due to no inherent conductor loss, relatively large bandwidth, simple coupling schemes to nearly all commonly used transmission lines, and the advantage of obtaining different radiation characteristics using different modes of the resonator. In this article, we give a comprehensive review of the modes and the radiation characteristics of DRs of different shapes, such as cylindrical, cylindrical ring, spherical, and rectangular. Further, accurate closed form expressions are derived for the resonant frequencies, radiation Q-factors, and the inside fields of a cylindrical DR. These design expressions are valid over a wide range of DR parameters. Finally, the techniques used to feed DR antennas are discussed. © 1994 John Wiley & Sons, Inc.

Dielectric resonator antennas—a review and general design relations for resonant frequency and bandwidth

Microstrip Radiators: Various Microstrip Antenna Configurations. Feeding Techniques and Modeling. Applications. Radiation Field. Surface Waves and Photonic Band-Gap Structures. Analytical Models for Microstrip Antennas: Transmission Line Model. Cavity Model. Generalized Cavity Model. Multi-port Network Model (MNM). Radiation Fields. Aperture Admittance. Mutual Admittance. Model for Coaxial Probe in Microstrip Antennas. Comparison of Analytical Models. Full-Wave Analysis of Microstrip Antennas: Spectral Domain Full-Wave Analysis. Mixed-Potential Integral Equation Analysis. Finite-Difference Time Domain Analysis.Rectangular Microstrip Antenna: Models for Rectangular Patch Antenna. Design Considerations for Rectangular Patch Antennas. Tolerance Analysis of Rectangular Microstrip Antennas. Mechanical Tuning of Patch Antennas. Quarter-wave Rectangular Patch Antenna. Circular Disk and Ring Antennas: Analysis of a Circular Disk Microstrip Antenna. Design Considerations for Circular Disk Antennas. Semicircular Disk and Circular Sector Microstrip Antennas. Comparison Of Rectangular And Circular Disk Microstrip Antennas. Circular Ring or Annular Ring Microstrip Antenna. Circular Sector Microstrip Ring Antenna. Microstrip Ring Antennas of Non-Circular Shapes. Dipoles and Triangular Patch Antennas: Microstrip Dipole and Center-Fed Dipoles. Triangular Microstrip Patch Antenna. Design of an Equilateral Triangular Patch Antenna. Microstrip Slot Antennas: Microstrip-Fed Rectangular Slot Antennas. CPW-Fed Slot Antennas. Annular Slot Antennas. Tapered Slot Antennas (TSA). Comparison of Slot Antennas with Microstrip Antennas. Circularly Polarized Microstrip Antennas and Techniques: Various Types of Circularly Polarized Microstrip Antennas. Singly-Fed Circularly Polarized Microstrip Antennas. Dual-Orthagonal Feed Circularly Polarized Microstrip Antennas. Circularly Polarized Traveling-Wave Microstrip-Line Arrays. Bandwidth Enhancement Techniques. Sequentially Rotated Arrays. Broad-Banding of Microstrip Antennas: Effect of Substrate Parameters on Bandwidth. Selection of Suitable Patch Shape. Selection of Suitable Feeding Technique. Multi-Moding Techniques. Other Broadbanding Techniques. Multifrequency Operation. Loaded Microstrip Antennas and Applications: Polarization Diversity Using Microstrip Antennas. Frequency Agile Microstrip Antennas. Radiation Pattern Control of Microstrip Antennas. Loading Effect of a Short. Compact Patch Antennas. Planar Inverted F Antenna. Dual-Frequency Microstrip Antennas. Dual-Frequency Compact Microstrip Antennas. Active Integrated Microstrip Antennas: Classification of Active Integrated Microstrip Antennas. Theory and Design of Active Integrated Microstrip Antenna Oscillators. Theory and Design of Active Integrated Microstrip Antenna Amplifiers. Frequency Conversion Active Integrated Microstrip Antenna Theory and Design. Design and Analysis of Microstrip Antenna Arrays: Parallel and Series Feed Systems. Mutual Coupling. Design of Linear Arrays. Design of Planar Arrays. Monolithic Integrated Phased Arrays.

Microstrip Antenna Design Handbook

This article presents a historical review of the research carried out on dielectric resonator antennas (DRAs) over the last three decades. Major research activities in each decade are highlighted. The current state of the art of dielectric-resonator-antenna technology is then reviewed. The achievable performance of dielectric resonator antennas designed for compactness, wide impedance bandwidth, low profiles, circular polarization, or high gain are illustrated. The latest developments in dielectric-resonator-antenna arrays and fabrication techniques are also examined.

Dielectric Resonator Antennas: A Historical Review and the Current State of the Art

This paper features some of the advances in dielectric-resonator antenna technology at the Communications Research Centre. Several novel elements are presented that offer significant enhancements to parameters such as impedance bandwidth, circular-polarization bandwidth, gain, or coupling to various feed structures. Several linear and planar arrays are also presented, to illustrate the performance of dielectric-resonator antenna elements in the array environment.

Recent advances in dielectric-resonator antenna technology

A dielectric resonator antenna system is disclosed wherein a dielectric material having a high dielectric constant is placed between a dielectric resonator antenna (DRA) and the antenna feed. Preferably the dielectric material having a high dielectric constant is either in the form of an insert within a cavity of the DRA or alternatively is in the form of a thin layer between the feed and the DRA for enhancing coupling therebetween. It is preferred that the high dielectric constant material be at least twice the value of the dielectric resonator antenna.

Broadband nonhomogeneous multi-segmented dielectric resonator antenna system

The multisegment dielectric resonator antenna (SDRA) has previously been developed to significantly enhance the coupling to a microstrip line. The MSDRA greatly facilitates the integration with a printed feed distribution network for use in a large array environment. The thickness and permittivity of the dielectric insert of the MSDRA can be adjusted to match the element impedance to that of the feed line. A detailed study of the effects of varying the dielectric insert parameters was carried out and useful guidelines are presented for the design of MSDRAs.

A. Ittipiboon

Papers

Microstrip Antenna Design Handbook

Dielectric Resonator Antennas: A Historical Review and the Current State of the Art

Recent advances in dielectric-resonator antenna technology

Broadband nonhomogeneous multi-segmented dielectric resonator antenna system

Design and analysis of multisegment dielectric resonator antennas