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

Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications. By Christophe Caloz and Tatsuo Itoh.

Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

Active metamaterials and metadevices: a review

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

This letter presents an omnidirectional horizontally polarized planar printed loop-antenna using left-handed CL loading with 50-Omega input impedance. The antenna has a one wavelength circumference and gives an omnidirectional pattern in the plane of the loop, whilst working in an n = 0 mode. In contrast, a conventional right-handed loop, with the same dimensions, has a figure of eight pattern in the plane of the loop. The antenna is compared with other right-handed periodically loading loop antennas and shown to have the best efficiency and is much easier to match. Design details and simulated results are presented. The concept significantly extends the design degrees of freedom for loop antennas.

Omnidirectional Loop Antenna With Left-Handed Loading

This letter presents a passive UHF printed loop antenna with left-handed loading. The RFID reader antenna can work at near- and far-field operation within the European UHF (865-868 MHz) band. The operation frequency and radiation properties can be modified by employing varactor diodes. Also, the antenna can work in the near-field region having a flat magnetic distribution in the interrogation zone. A comparative study with other passive RFID reader conventional antennas shows that the left-handed loop achieves stronger near H-field with good impedance matching. Design details, simulated results, and a fabricated prototype are presented. The concept significantly extends the design degrees of freedom for RFID antennas.

A Reconfigurable Passive UHF Reader Loop Antenna for Near-Field and Far-Field RFID Applications

Recently, a new empty coaxial structure, entirely built with printed circuit boards, has been proposed. The resulting coaxial line has low radiation, low losses, high-quality factor, and is nondispersive. Up to now, this coaxial line has not been completely integrated in a planar substrate, since a working transition to a traditional planar line has not been defined yet. Therefore, in this paper, a high-quality transition from coplanar waveguide to this new empty coaxial line is proposed. With this transition, the coaxial line is completely integrated in a planar circuit board, so that it truly becomes an empty substrate-integrated coaxial line. The proposed transition has been fabricated. Both full-wave simulated and measured results show an excellent agreement. Therefore, the proposed transition is suitable to develop completely substrate-integrated components for applications in wideband communication systems that require very high quality responses and protection from external interferences. To show this fact, this new transition has been applied to integrate a high-performance empty coaxial filter in a planar substrate. The measured response of this filter is excellent, and proves the goodness of the proposed transition that has enabled, for the first time, the complete integration of an empty coaxial line in a planar substrate.

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High-Performance Coplanar Waveguide to Empty Substrate Integrated Coaxial Line Transition

A study of the efficiency of small dipole antennas loaded with a left-handed transmission line is described. The antenna is composed of a ladder network periodic structure of a number of unit cells. Left-handed performance can be obtained in straight or meandered capacitive-inductive (CL) lumped loading. Its performance is compared to a right-handed dipole with inductive (L) lumped loading. Differently loaded dipoles with four unit cells with the same size reduction have been compared. Right-handed loading gives the best efficiency as expected, but left-handed loading shows the greater degree of freedom to achieve a desired impedance at the terminals. The efficiency is also increased when the CL-loaded dipole is meandered, because of the higher radiation resistance. Moreover, different numbers of unit cell have been compared in order to clarify the number for the best efficiency with size reduction. In a low-order mode, an inductively loaded dipole has highest efficiency for two unit cells, with reduced efficiency with the number of loading elements. However, the reverse is true for the CL-loading. The efficiency of a meandered CL-loaded dipole becomes comparable to the conventional L-loading for higher than four cells. CL-loading with higher mode number gives higher efficiency than a conventional dipole with multiple inductive loads.

Efficiency of Electrically Small Dipole Antennas Loaded With Left-Handed Transmission Lines

In this letter, an empty substrate integrated waveguide H-plane sectorial horn antenna is presented. The antenna is integrated within a planar substrate and is fed by means of a microstrip transmission line. It is composed of a partially empty substrate layer stacked between two cover metallic plates. Results obtained for a prototype designed and fabricated at Ku-band show a measured efficiency close to 90% and matched responses. No extra loading elements are needed in order to reduce reflection at the end of the aperture conversely to previous designs. Moreover, the structure is quite simple and cheap and does not depend on substrate characteristics, i.e., dielectric permittivity or loss tangent. This new methodology for manufacturing substrate integrated antennas without dielectric considerably improves the performance of conventional substrate integrated horn antennas.

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Alejandro L. Borja

Papers

Omnidirectional Loop Antenna With Left-Handed Loading

A Reconfigurable Passive UHF Reader Loop Antenna for Near-Field and Far-Field RFID Applications

High-Performance Coplanar Waveguide to Empty Substrate Integrated Coaxial Line Transition

Efficiency of Electrically Small Dipole Antennas Loaded With Left-Handed Transmission Lines

Highly Efficient and Well-Matched Empty Substrate Integrated Waveguide H-Plane Horn Antenna