Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

A Wide Frequency Scanning Printed Bruce Array Antenna with Bowtie and Semi-Circular Elements

A printed edge-fed counterpart of the wire Bruce array antenna, for frequency scanning applications, is presented in this paper. The unit-cell of the proposed antenna consists of bowtie and semi-circular elements to achieve wide bandwidth from below 22 GHz to above 38 GHz with open-stopband suppression. The open-stopband suppression enables a wide seamless scanning range from backward, through broadside, to forward endfire. A sidelobe threshold level of −10 dB is maintained to evaluate efficient scanning performance of the antenna. The antenna peak realized gain is 15.30 dBi, and, due to its compact size, has the ability to scan from −64° to 7

A New Silicon-Based Dielectric Waveguide Technology for Millimeter-Wave/Terahertz Devices and Integrated Systems

In recent decades, the millimeter-Wave (mmWave)/THz band has attracted great attention in the research community. The Terahertz frequency band runs from approximately 300 GHz to 3 THz, an incredible 2700 GHz of bandwidth. The Terahertz frequency range has traditionally been considered as the RF "no man's land", between electronic and optical technologies. Many efforts have been made to extend existing active and passive devices to take advantage of these higher frequencies. The development of a universal technology for integrating various functionalities in the THz region is the ultimate goal of many researchers. The primary focus of this research is to develop a novel silicon waveguide-based technology for implementing various structures and devices in the mmWave and THz range of frequencies. The structures introduced in this study are designed based on High Resistivity Silicon (HRS). Two technologies are developed and investigated at the Centre for Intelligent Antenna and Radio Systems (CIARS): Silicon-On-Glass (SOG) and Silicon Image Guide (SIG) technologies. The proposed technologies provide a low-cost, highly efficient, and integratable platform for realization a variety of mmWave/THz systems suitable for various applications such as sensing, communication, and imaging. A comprehensive study is conducted for functionality and error analysis of the proposed technologies. Also, a vast range of passive structures such as bends, dividers, and couplers are designed, fabricated and successfully tested with desired performance at the mmWave range of frequencies. Additionally, three types of dielectric waveguide antennas are designed and optimized: parasitic tapered antenna, groove grating antenna, and strip grating antenna. Another focus of this thesis is to investigate the behavior of resonance structures, operating based on Whispering Gallery Modes (WGMs). The WG mode is a special type of high order mode of a circular shaped resonator, and offers very unique properties, which make it very suitable for sensing applications. In this research, an efficient algorithm is developed for analyzing the WGM resonators. Then, the proposed HRS platforms are used for implementing various WGM resonance configurations. The introduced WGM structures are employed for two major applications: DNA sensing and resonance tuning. The results for DNA testing are quite impressive in being able to distinguish between different kinds of DNA. To demonstrate the usefulness of the developed HRS structures, a number of complex systems including, a Butler matrix network, a finger-shaped phase shifter, and tunable WGM resonance structures are designed, optimized, and realized in this report. As part of this research, a novel Microwave-Photonic idea is proposed for sensing purposes. The core of the system is based on the WGM resonance structures implemented on the HRS platforms. The proposed system is tested and promising results are achieved.4 month

Study of mm-wave Fixed Beam and Frequency Beam-Scanning Antenna Arrays

Millimeter-wave frequencies are anticipated to be widely adapted for future wireless communication systems to resolve the demand of high data-rate and capacity issues. The millimeter-wave frequency range offers wide spectrum and a shift for most newly developing technologies as the microwave and lower frequency bands are becoming overcrowded and congested. These high frequency bands offer short wavelengths which has enabled the researchers to design and implement compact and adaptable antenna solutions. This research focuses on the implementation, transformation and modification of antenna structures used in lower frequency bands to millimeter-wave applications with high gain and multi-band and wideband performances. The first part of the thesis presents a microstrip patch array antenna with high gain in the upper 26 GHz range for 5G applications. The tolerance of the antenna, on widely used Rogers RT/duroid 5880 substrate, is observed with the edge-fed structure when curved in both concave and convex directions. In the second part of the thesis, 20 rectangular loops are arranged in a quasi-rhombic shaped planar microstrip grid array antenna configuration with dual-band millimeter-wave performance. A comparison with equal sized microstrip patch array is also presented to analyse the performance. The antenna operates in the upper 26 GHz band and has two frequency bands in close proximity. The third part of the thesis discusses the transition from wire Bruce array antenna to planar technology. Having been around for nearly a century and despite the simplicity of structure, the research community has not extended the concept of Bruce array antenna for further research. The proposed planar Bruce array antenna operates in three frequency v bands with optimization focus on 28.0 GHz band that has a directive fan-beam radiation pattern at broadside whereas the other two frequency ranges, above 30 GHz, have dual-beam radiation patterns which provide radiation diversity in narrow passages. The final part of the thesis deals with the transformation and modification of wire Bruce array antenna geometry to edge-fed printed leaky-wave antennas for millimeter-wave frequency scanning applications. In the first approach, the lengths of the unit-cell are optimised, without any additional circuitry, to enable two scanning ranges and mitigate the Open-Stopband, at broadside, for seamless scanning in the first range. A Klopfen-stein tapered divider is then deployed to make a linear array of the proposed antenna to achieve high gain. In the second approach, the horizontal and vertical lengths of the meandered unit-cell are replaced with semi-circular and novel bowtie elements, respectively, to obtain wide scanning range. The numerical results and optimizations have been performed using CST Micro-wave Studio where the effects of metallization and dielectric losses are properly consid-ered. The prototypes of the proposed antennas have been fabricated and experimentally validated

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium