With the increasing demand for high performance communication networks and the proliferation of mobile devices, significant advances in antenna design are essential. In recent years the rising demands of the mobile wireless communication industry have forced antennas to have increased performance while being limited to an ever decreasing footprint. Such design constraints have forced antenna designers to consider frequency agile antennas so that their behavior can adapt with changing system requirements or environmental conditions. Frequency agile antennas used for mobile handset applications must also be inexpensive, robust, and make use of electronic switching with reasonable DC power consumption. Previous works have addressed a number of these requirements but relatively little work has been performed on frequency agile dielectric resonator antennas (DRAs). The objective of this thesis is to investigate the use of DRAs for frequency reconfigurability. DRAs are an attractive option due to their compactness, very low losses leading to high radiation efficiencies (better than 95%) and fairly wide bandwidths compared to alternatives. DRA’s are also well suited for mobile communications since they can be placed on a ground plane and are by nature low gain antennas whose radiation patterns typically resemble those of short electric or magnetic dipoles. One way to electronically reconfigure a DRA, in the sense of altering the frequency band over which the input reflection coefficient of the antenna is below some threshold, is to partially load one face of the DRA with a conducting surface. By altering the way in which this surface connects to the groundplane on which the DRA is mounted, the DRA can be reconfigured due to changes in its mode structure. This connection was first made using several conducting tabs which resulted in a tuning range of 69% while having poor cross polarization performance. In order to address the poor cross polarization performance a second conducting surface was placed on the opposing DRA wall. This technique significantly reduced the cross polarization levels while obtaining a tuning range of 83%. The dual-wall conductively loaded DRA was then extended to include a full electronic implementation using PIN diodes and varactor diodes in order to achieve discrete and continuous tuning respectively. The two techniques both achieved discrete tuning ranges of 95% while the varactor implementation also had a continuous tuning range of 59% while both maintaining an acceptable cross polarization level.

abstract: The mechanism of loss in high performance microwave dielectrics with complex perovskite structure, including Ba(Zn1/3Ta2/3)O3, Ba(Cd1/3Ta2/3)O3, ZrTiO4-ZnNb2O6, Ba(Zn1/3Nb2/3)O3, and BaTi4O9-BaZn2Ti4O11, has been investigated. We studied materials synthesized in our own lab and from commercial vendors. Then the measured loss tangent was correlated to the optical, structural, and electrical properties of the material. To accurately and quantitatively determine the microwave loss and Electron Paramagnetic Resonance (EPR) spectra as a function of temperature and magnetic field, we developed parallel plate resonator (PPR) and dielectric resonator (DR) techniques. Our studies found a marked increase in the loss at low temperatures is found in materials containing transition metal with unpaired d-electrons as a result of resonant spin excitations in isolated atoms (light doping) or exchange coupled clusters (moderate to high doping) ; a mechanism that differs from the usual suspects. The loss tangent can be drastically reduced by applying static magnetic fields. Our measurements also show that this mechanism significantly contributes to room temperature loss, but does not dominate. In order to study the electronic structure of these materials, we grew single crystal thin film dielectrics for spectroscopic studies, including angular resolved photoemission spectroscopy (ARPES) experiment. We have synthesized stoichiometric Ba(Cd1/3Ta2/3)O3 [BCT] (100) dielectric thin films on MgO (100) substrates using Pulsed Laser Deposition. Over 99% of the BCT film was found to be epitaxial when grown with an elevated substrate temperature of 635 C, an enhanced oxygen pressures of 53 Pa and a Cd-enriched BCT target with a 1 mol BCT: 1.5 mol CdO composition. Analysis of ultra violet optical absorption results indicate that BCT has a bandgap of 4.9 eV. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2013

Materiais dielétricos para operação em microondas constituem um ponto importante para usos em sistemas de comunicação móvel/via satélite, incluindo sistemas de monitoramento terrestres, internet/telefonia para celulares, internet das coisas, além do interesse militar para elaboração de radares. Avanços importantes nesse setor tecnológico só foram outorgados, graças ao emprego ostensivo de ressoadores dielétricos (RDs). Esses dispositivos constituem cerâmicas óxidas com baixa perda dielétrica em microondas, com demanda para sua miniaturização. O sistema deverá possuir alta constante dielétrica nesse intervalo e o dispositivo deve ser termicamente estável, ou seja, suas propriedades dielétricas não se alterarão com a temperatura. A busca por materiais de alto desempenho resultou na descoberta das perovskitas ordenadas 1:1 e 1:2, com estequiometria A2BBO6 e A3BB2O9, respectivamente. Tais sistemas ordenam o sítio B, da perovskita ABO3, gerando o empilhamento dos planos cristalinos com B e B, intercalados e na direção [1 1 1]c. Os resultados da literatura mostram que o ordenamento possui papel fundamental na obtenção de ressoadores de baixa perda dielétrica. Ademais, poucos estudos reportam as propriedades dos sistemas contendo os cátions Ca e Nb, no sítio B. Portanto, essa tese dedicou-se à investigação das propriedades dielétricas do sistema Ba3CaNb2O9 e, posteriormente, a modificação desse com a substituição dos cátions Ba2+ por Sr2+ e La3+. As amostras foram preparadas pelo método de reação do estado sólido e, posteriormente, caracterizadas pela difração de raios X, espalhamento Raman, espectroscopia de impedância e desempenho em microondas, além de técnicas complementares como análise térmica, densidade por imersão e microscopia eletrônica de varredura. Os resultados demonstraram a coexistência dos domínios 1:1 e 1:2 no sistema Ba3CaNb2O9, sendo possível manipulá-los mediante condições da sinterização. Microestruturalmente, esses domínios são regiões no cristalito com diferentes ordens catiônicas e, assim, com propriedades cristalográficas e vibracionais diferentes. Pela impedância, notou-se que o ressoador Ba3CaNb2O9 tende a conduzir mais quando possui uma tendência para o domínio 1:1. Tal resultado foi confirmado em microondas, onde a redução da perda dielétrica foi correlacionada à diminuição do domínio 1:1 na estrutura cristalina dos ressoadores. Na solução sólida com Sr2+, uma transição da fase trigonal D3d3 para monoclínica C2h3 foi detectada nos pós-calcinados, sendo oriunda das inclinações octaédricas do sistema de Glazer a0b-b-. As cerâmicas desse sistema foram sinterizadas a 1500 °C por 26 h, cujo resultado ilustrou uma tendência à ordem 1:1 para x ≥ 0,30. No sistema com La3+, observou-se, além da coexistência, os monodomínios 1:1 e 1:2. O sistema com monodomínios 1:1, BaLaCaNbO6 (y = 0,50), evidenciou uma distorção monoclínica intrínseca. Esta distorção foi associada às inclinações octaédricas do sistema de Glazer a0b-b-, reduzindo a simetria da fase cúbica Oh5 para monoclínica C2h3. Por fim, o desempenho como ressoador dielétrico dos sistemas BaLaCaNbO6 e Ba3CaNb2O9 foi avaliado. O primeiro sistema mostrou os seguintes valores: permissividade relativa εg ∼ 26, Qu × fR ∼ 10.506 GHz e coeficiente τf ∼ -55 ppm.K-1. O segundo sistema revelou os dados: permissividade εg ∼ 43, Qu × fR ∼ 15.752 GHz e o coeficiente τf ∼ 278 ppm.K-1. / Dielectric materials for microwave applications play an important role in mobile and satellite communication systems, including terrestrial monitoring, internet/mobile devices, internet of things, as well as the military uses as the radar developments. Advances in this technological field were only possible due to the ostensive use of dielectric resonators (DRs). These devices constitute oxide ceramics with a low dielectric loss in microwave frequency. The system must have high dielectric constant and such a device must be thermally stable. The search for highperformance materials granted the discovery of 1:1 and 1:2 ordered perovskites, with general formula A2BBO6 and A3BB2O9, respectively. These systems depict the B-site ordering of ABO3 perovskite, inducing the crystalline planes stacking in the [1 1 1]c direction. The literature results showed that the ordering plays an essential role in the low loss ceramics. Moreover, few studies reported the features of the systems containing the Ca and Nb cations at the B-site. Therefore, our work drives the dielectric properties of the Ba3CaNb2O9 system and, then, the modification induced by Ba2+ substitution by Sr2+ and La3+. The samples were prepared by the conventional solid-state reaction method and probed by X-ray diffraction, Raman scattering, impedance spectroscopy and microwave performance, as well as other techniques such as thermal analysis, density measurement, and electron microscopy. Our findings elucidated the coexistence of 1:1 and 1:2 domains in Ba3CaNb2O9 ceramics, being possible to manipulate them by sintering conditions. Such an ordered domain denotes regions in the crystallites with different cationic order and with different crystallographic and vibrational behavior. By the impedance spectroscopy, it was observed that Ba3CaNb2O9 ceramics tend to conduct more when they present a tendency towards the 1:1 domains. The earlier result was also confirmed in microwave frequency, in which the dielectric loss decreasing was correlated to the decrease of the 1:1 domain in the crystal structure. In the strontium solid solution, a transition from the D3d3 trigonal phase to the C2h3 monoclinic one was noted in powder samples, being derived from octahedral tilting (a0b-b- Glazer system). In the lanthanum system, besides the coexistence, the monodomains 1:1 and 1:2 were observed. Otherwise, the 1:1 monodomain system, BaLaCaNbO6 (y = 0.50), exhibited an intrinsic monoclinic distortion. This distortion was ascribed to the octahedral tilting (a0b-b- Glazer system), lowering the crystal symmetry from Oh5 cubic phase to the C2h3 monoclinic phase. The dielectric resonator performances of the BaLaCaNbO6 and Ba3CaNb2O9 systems were evaluated. The first system showed the following values: permittivity εg ∼ 26, Qu × fR ∼ 10.506 GHz and coefficient τf ∼ -55 ppm.K-1. The second system exhibited the data: permittivity εg ∼ 43, Qu × fR ∼ 15.752 GHz and coefficient τf ∼ 278 ppm.K-1.

In this thesis a technique that is being used in another area of technology to optimize light reception in a photographic camera was also applied to the dielectric resonator antenna. The technique consisting of the use of thin film to couple the media and camera impedances resulted in a dielectric resonator antenna bandwidth enhancement technique. The bandwidth enhancement technique was found when thin film dielectric layer structure was used to couple the dielectric resonator and its feed mechanism. Remarkable good performance was detected with a coplanar waveguide fed cylindrical dielectric resonator antenna which resulted in an improvement to its fractional bandwidth from 7.41% to 50.85%. Extensive experimental work was undertaken in order to explore the extent offered in bandwidth performance by using thin film dielectric layer structure in the dielectric resonator antenna performance. The experimental tasks were designed in order to investigate the influence of the thin film dielectric layer structure in relation to its size, shape, thickness, position and direction. Experimental results were supported with simulation work with the computer simulation technology microwave studio. The pieces of the material used for undertaking this experimental work were manually handcrafted. Four different dielectric resonator antenna designs were used in order to carry out the experimental work including the coplanar waveguide fed cylindrical dielectric resonator antenna. The other three dielectric resonator antennas were implemented using the same microstrip feed mechanism. Improved performance in bandwidth was achieved for all the designs. Optimization of the incoming signal was observed when a piece of thin film dielectric layer structure was placed in position between the feed mechanism and the dielectric resonator antenna. The optimization was observed as an enhancement in both the return loss level and the bandwidth of work. Different unexpected operational modes from were activated, such modes being called perturbed modes. Two different shapes were used in this project. Cylindrical dielectric resonator antenna (ɛr = 37) from a commercial provider and two novel rectangular dielectric resonator antennas. The novel rectangular dielectric resonator antennas were created with the methodology presented in this thesis. The rectangular dielectric resonator antennas were elaborated with transparent ceramic material (ɛr = 7) and TMM10i (ɛr = 9.8) from the Rogers Corporation company. The bandwidth enhancement technique was tested in novel embedded dielectric resonator antennas. A coplanar waveguide fed embedded cylindrical dielectric resonator antenna achieved a maximum bandwidth enhancement of 156.77% around f = 3.79 GHz with a thin film dielectric layer structure modified rectangular piece on one edge. Escalation to dielectric resonator antenna design at millimeter wave frequencies was achieved by using thin film dielectric layer structure bandwidth enhancement technique and a handcrafted printed circuit board millimeter wave feed mechanism. The millimeter wave feed mechanisms were achieved using a low cost alternative technique conceived as part of this project. Millimeter wave dielectric resonator antennas were implemented using thin film dielectric layers structure. The antennas deliver an adequate performance in bandwidth. The work presented in this thesis demonstrates dielectric resonator antenna simpler geometry, simple couple schemes, small size, low profile, light weight, and ease of excitation and orientation. Other parameters have also been investigated covering reduced complexity, high degree of flexibility, ease of fabrication and the use of low cost technology to escalate to millimeter wave frequencies.

Thesis (PhD (Electrical Engineering))--Cape Peninsula University of Technology, 2019 / This dissertation presents a concept for a compact, low-profile, integrated solar panel antenna for use on small satellites in low Earth orbit. To date, the integrated solar panel antenna design approach has primarily been, patch (transparent or non-transparent) and slot radiators. The design approach presented here is proposed as an alternative to existing designs. A prototype, comprising of an optically transparent rectangular dielectric resonator was constructed and can be mounted on top of a solar panel of a Cube Satellite. The ceramic glass, LASF35 is characterised by its excellent transmittance and was used to realise an antenna which does not compete with solar panels for surface area. Currently, no closed-form solution for the resonant frequency and Q-factor of a rectangular dielectric resonator antenna exists and as a first-order solution the dielectric waveguide model was used to derive the geometrical dimensions of the dielectric resonator antenna. The result obtained with the dielectric waveguide model is compared with several numerical methods such as the method of moments, finite integration technique, radar cross-section technique, characteristic mode analysis and finally with measurements. This verification approach was taken to give insight into the resonant modes and modal behaviour of the antenna. The interaction between antenna and a triple-junction gallium arsenide solar cell is presented demonstrating a loss in solar efficiency of 15.3%. A single rectangular dielectric resonator antenna mounted on a ground plane demonstrated a gain of 4.2 dBi and 5.7 dBi with and without the solar cell respectively. A dielectric resonator antenna array with a back-to-back Yagi-Uda topology is proposed, designed and evaluated. The main beam of this array can be steered can steer its beam ensuring a constant flux density at a satellite ground station. This isoflux gain profile is formed by the envelope of the steered beams which are controlled using a single digital phase shifter. The array achieved a beam-steering limit of ±66° with a measured maximum gain of 11.4 dBi. The outcome of this research is to realise a single component with dual functionality satisfying the cost, size and weight requirements of small satellites by optimally utilising the surface area of the solar panels.

Ultra wide-band (UWB) technology is considered one of the very promising wireless technologies in the new millennium. This increases the demand on designing UWB antennas that meet the requirements of different UWB systems. In this dissertation, different UWB antennas are proposed such as an antenna that covers almost the entire UWB bandwidth, 3.5-11 GHz, as defined by the federal communication commission (FCC). This antenna has a size of 50×40×1.5mm3. Miniaturized worldwide UWB antennas are also introduced. Miniaturized worldwide UWB antennas that have compact sizes of (30×20×1.5) mm3, and (15×15×1.5) mm3 are also investigated. The designed worldwide UWB antennas cover the UWB spectrums defined by the electronic communication committee (ECC), 6-8.5 GHz, and the common worldwide UWB spectrum, 7.4-9 GHz. A system consisting of two identical antennas (transmitter and receiver) is built in the Antennas and Propagation Lab at Southern Illinois University Carbondale (SIUC) to test the coupling properties between every two identical antennas. The performance of that system is analyzed under different ii conditions to guarantee that the transmitted signal will be correctly recovered at the receiver end. The designed UWB antennas can be used in many short range applications such as wireless USB. Wireless USB is used in PCs, printers, scanners, laptops, MP3 players, hard disks and flash drives. A new technique is introduced to widen the impedance bandwidth of dielectric resonator antennas (DRAs). DRA features compactness, low losses, and wideband antennas. Different compact UWB DRAs are investigated in this dissertation. The designed DRAs cover a wide range of frequency bands such as, 6.17-24GHz, 4.23-13.51GHz, and 4.5-13.6GHz. The designed DRAs have compact sizes of 1×1×1.5cm3, 0.9×0.9×1.32cm3, 0.6×0.6×1cm3, and 0.6×0.6×0.9cm3; and cover the following frequency bands 4.22-13.51GHz, 4.5-13.6GHz, 6.1-23.75GHz, and 6.68-26.7GHz; respectively. The proposed DRAs may be used for applications in the X, Ku and K bands such as military radars and unmanned airborne vehicles (UAV).

With the increasing demand for high performance communication networks and the proliferation of mobile devices, significant advances in antenna design are essential. In recent years the rising demands of the mobile wireless communication industry have forced antennas to have increased performance while being limited to an ever decreasing footprint. Such design constraints have forced antenna designers to consider frequency agile antennas so that their behavior can adapt with changing system requirements or environmental conditions. Frequency agile antennas used for mobile handset applications must also be inexpensive, robust, and make use of electronic switching with reasonable DC power consumption. Previous works have addressed a number of these requirements but relatively little work has been performed on frequency agile dielectric resonator antennas (DRAs). The objective of this thesis is to investigate the use of DRAs for frequency reconfigurability. DRAs are an attractive option due to their compactness, very low losses leading to high radiation efficiencies (better than 95%) and fairly wide bandwidths compared to alternatives. DRA’s are also well suited for mobile communications since they can be placed on a ground plane and are by nature low gain antennas whose radiation patterns typically resemble those of short electric or magnetic dipoles. One way to electronically reconfigure a DRA, in the sense of altering the frequency band over which the input reflection coefficient of the antenna is below some threshold, is to partially load one face of the DRA with a conducting surface. By altering the way in which this surface connects to the groundplane on which the DRA is mounted, the DRA can be reconfigured due to changes in its mode structure. This connection was first made using several conducting tabs which resulted in a tuning range of 69% while having poor cross polarization performance. In order to address the poor cross polarization performance a second conducting surface was placed on the opposing DRA wall. This technique significantly reduced the cross polarization levels while obtaining a tuning range of 83%. The dual-wall conductively loaded DRA was then extended to include a full electronic implementation using PIN diodes and varactor diodes in order to achieve discrete and continuous tuning respectively. The two techniques both achieved discrete tuning ranges of 95% while the varactor implementation also had a continuous tuning range of 59% while both maintaining an acceptable cross polarization level.

Yes / The antenna array designed to operate over 0.450-0.475 Terahertz comprises two dielectric resonators (DRs) that are stacked vertically on top of each other and placed on the surface of the slot antenna fabricated on a silicon substrate using standard CMOS technology. The slot created in the silicon substrate is meandering and is surrounded by metallic via-wall to prevent energy dissipation. The antenna has a maximum gain of 4.5dBi and radiation efficiency of 45.7% at 0.4625 THz. The combination of slot and vias transform the antenna to a metamaterial structure that provides a relatively small antenna footprint. The proposed series-fed double DRs on-chip antenna array is useful for applications in THz integrated circuits. / Partially supported by innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E0/22936/1.

With the rapid advancement of autonomous vehicles, reliable and efficient wireless communication systems with high data rates have become essential for their safe and efficient operation and further evolution. High data rates are found in the higher frequency bands where conductive antennas lack radiation efficiency. To achieve high radiation efficiency, researchers tend towards using Circular Polarized Dielectric Resonator Antennas (CP-DRA). However, there is a lack of studies that cover the FR2 5G bands n257, n258, n261 suggested by 3GPP which is needed if vehicles were to drive across regional borders. This project addresses the challenges of achieving suitable CP-DRA performance for autonomous vehicle communication aimed at covering these FR2 5G bands. The objective is to design and simulate an optimized CP-DRA antenna that meets the required performance characteristics for further use in a phased array for efficient communication in the high-frequency FR2 5G bands. The objective was fulfilled by producing a model of a CP-DRA antenna that covers the mentioned FR2 5G bands. The antenna array achieves this with an axial ratio beam width at plus/minus 20 degrees azimuth angle and peak gain of 9-12 dBi throughout the frequency range. The model consists of four cylindrical resonator antenna elements excited in phase quadrature by a slot aperture feeding network to accomplish the circular polarization. The radiation efficiency of the model is 94% throughout the frequency range with an impedance bandwidth of < -15 dB. A prototype was built and tested that vaguely verified the beam pattern and center frequency. Future work includes building a prototype more comparable to the model for further verification of the circularly polarized gain pattern.

Yes / In this paper, a compact two-element cylindrical dielectric resonator antenna (CDRA) array with corporate feeding is proposed for X-band applications. The dielectric resonator antenna (DRA) array is excited by a microstrip feeder using an efficient aperture-coupled method. The designed array antenna is analyzed using a CST microwave studio. The fabricated sample of the proposed CDRA antenna array showed bandwidth extending from 10.42GHz to 12.84GHz (20.8%). The achieved array gain has a maximum of 9.29dBi at frequency of 10.7GHz. This is about 2.06dBi enhancement of the gain in comparison with a single pellet CDRA. The size of the whole antenna structure is about 50 x 50mm2.