This letter presents a new metamaterial-based waveguide technology referred to as ridge gap waveguides. The main advantages of the ridge gap waveguides compared to hollow waveguides are that they are planar and much cheaper to manufacture, in particular at high frequencies such as for millimeter and sub- millimeter waves. The latter is due to the fact that there are no mechanical joints across which electric currents must float. The gap waveguides have lower losses than microstrip lines, and they are completely shielded by metal so no additional packaging is needed, in contrast to the severe packaging problems associated with microstrip circuits. The gap waveguides are realized in a narrow gap between two parallel metal plates by using a texture or multilayer structure on one of the surfaces. The waves follow metal ridges in the textured surface. All wave propagation in other directions is prohibited (in cutoff) by realizing a high surface impedance (ideally a perfect magnetic conductor) in the textured surface at both sides of all ridges. Thereby, cavity resonances do not appear either within the band of operation. The present letter introduces the gap waveguide and presents some initial simulated results.

Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates

Preface 1. Introduction 2. FDTD Method for periodic structure analysis 3. EBG Characterizations and classifications 4. Design and optimizations of EBG structures 5. Patch antennas with EBG structures 6. Low profile wire antennas on EBG surfaces 7. Surface wave antennas Appendix: EBG literature review.

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Electromagnetic Band Gap Structures in Antenna Engineering

To make transportation safer, more efficient, and less harmful to the environment, traffic telematics services are currently being intensely investigated and developed. Such services require dependable wireless vehicle-to-infrastructure and vehicle-to-vehicle communications providing robust connectivity at moderate data rates. The development of such dependable vehicular communication systems and standards requires accurate models of the propagation channel in all relevant environments and scenarios. Key characteristics of vehicular channels are shadowing by other vehicles, high Doppler shifts, and inherent nonstationarity. All have major impact on the data packet transmission reliability and latency. This paper provides an overview of the existing vehicular channel measurements in a variety of important environments, and the observed channel characteristics (such as delay spreads and Doppler spreads) therein. We briefly discuss the available vehicular channel models and their respective merits and deficiencies. Finally, we discuss the implications for wireless system design with a strong focus on IEEE 802.11p. On the road towards a dependable vehicular network, room for improvements in coverage, reliability, scalability, and delay are highlighted, calling for evolutionary improvements in the IEEE 802.11p standard. Multiple antennas at the onboard units and roadside units are recommended to exploit spatial diversity for increased diversity and reliability. Evolutionary improvements in the physical (PHY) and medium access control (MAC) layers are required to yield dependable systems. Extensive references are provided.

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Vehicular Channel Characterization and Its Implications for Wireless System Design and Performance

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

Smart world is envisioned as an era in which objects (e.g., watches, mobile phones, computers, cars, buses, and trains) can automatically and intelligently serve people in a collaborative manner. Paving the way for smart world, Internet of Things (IoT) connects everything in the smart world. Motivated by achieving a sustainable smart world, this paper discusses various technologies and issues regarding green IoT, which further reduces the energy consumption of IoT. Particularly, an overview regarding IoT and green IoT is performed first. Then, the hot green information and communications technologies (ICTs) (e.g., green radio-frequency identification, green wireless sensor network, green cloud computing, green machine to machine, and green data center) enabling green IoT are studied, and general green ICT principles are summarized. Furthermore, the latest developments and future vision about sensor cloud, which is a novel paradigm in green IoT, are reviewed and introduced, respectively. Finally, future research directions and open problems about green IoT are presented. Our work targets to be an enlightening and latest guidance for research with respect to green IoT and smart world.

Green Internet of Things for Smart World

The present invention represents a new, way of packaging passive and active microwave circuits, and in particular circuits involving microstrip transmission lines and similar substrate bound transmission lines. The circuits are located between two conducting surfaces, one of these surface may be the ground plane of the microwave circuit, and at least one of these surfaces are provided with conducting elements formed as angular or curved conducting lines arranged on substrates. The conducting lines may e.g. have a zigzag shape. The two surfaces may form the bottom and lid of a cavity with conducting sidewalls. The conducting elements may with advantage be arrange in a periodic grid, and create together with the ground plane of the microwave circuit board or the smooth metal plane below the microwave circuit board a stop band for waves propagating between the lid with conducting elements and the ground plane. Thereby, cavity resonances are avoided or suppressed that otherwise create a big problem associated with the packaging in metal boxes with smooth metal walls.

Packaging of active and passive microwave circuits using a grid of planar conducting elements on a grid of vertically arranged substrates

An array of leaky wave antennas is presented. To create the array, leaky wave antennas in gap waveguide technology are stacked. The distance between the array elements, and the feeding network are studied to achieve maximum directivity and to avoid side effects that reduce the efficiency of the design. The aiming band is that of 92-96 GHz, and the directivity enhancement using an array of four stacked leaky wave antennas is 5 dB, reaching 25 dB, in comparison to the single antenna directivity of 19.9 dB.

Array of stacked leaky wave antennas based on gap waveguide technology

A new design methodology for dual band leaky-wave antennas is presented in the paper. The proposed methodology is based on the use of a single partial reflective surface (PRS) made with a Frequency Selective Surface (FSS) that fulfills the resonant condition at two different frequencies. This allows the design of a dual band leaky wave antenna including the control on the directivity at each one of the frequencies. Two examples of the application of this method (one with identical directivities at the two frequencies and the other one with different directivities) are presented.

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Single-Layer Dual-Band Leaky Wave Antennas Design Methodology with Directivity Control

The purpose of this paper is to present hybrid algorithms made by mixing gradient and evolutive algorithms, as a solution to solve electromagnetic problems. Specifically, array synthesis has been chosen to show the functionality of these methods. In this work the discussion was focused on the comparison of the traditional evolutionary algorithm (based on the Darwinian theories), with the most common hybrid algorithms (inspired on Baldwin effect and Lamarckian evolution by Michaelewicz and Fogel, 2004) in some examples of array synthesis.

Hybrid algorithms on antenna design

In this paper, the design of an array in groove gap waveguide technology is developed. The basic element of the array is a leaky-wave antenna made in gap waveguide technology. The array is formed by stacking leaky-wave antennas one on top of the other. The design of the array consists on the investigation of the number of elements to be stacked, and the inter-element distance to avoid grating lobes and to obtain high directivity levels. The feeding of the array is done through the design of a vertical coupler. Phase shifters placed after the feeding network, ensure that all the elements radiate in-phase, aiming to achieve maximum directivity. The central frequency of the design is 28 GHz, and the array of four elements, achieves an enhancement of +5dB, reaching 24.5 dB of directivity, in comparison to 19.6 dB of directivity of the single leaky-wave antenna made in this technology. The proposed design was validated experimentally with a prototype.

Eva Rajo-Iglesias

Papers

Packaging of active and passive microwave circuits using a grid of planar conducting elements on a grid of vertically arranged substrates

Array of stacked leaky wave antennas based on gap waveguide technology

Single-Layer Dual-Band Leaky Wave Antennas Design Methodology with Directivity Control

Hybrid algorithms on antenna design

Design of an array of stacked groove gap waveguide leaky-wave antennas in the Ka band