No description available.

Dual-band antenna elements that support dual-polarization provide ideal performance for applications including space-based platforms, multifunction radar, wireless communications, and personal electronic devices. In many communications and radar applications, a dual-band, dual-polarization antenna array becomes a requirement in order to produce an electronically steerable, directional beam capable of supporting multiple functions. The multiple polarizations and frequency bands allow the array to generate multiple simultaneous beams to support true multifunction radar. Many of the applications in spaced-based systems and personal electronic devices have strict restraints on the size and weight of the antenna element, favoring a low-profile, lightweight device. The research performed in this dissertation focuses on the design of a dual-band, dual-polarized antenna element capable of operating as an isolated element or in an array environment. The element contains two concentric, dual-polarized radiators. The low band radiator is a shorted square ring antenna, and the high band radiator is a square ring slot. Each constituent element achieves circular polarization through the introduction of triangular perturbations into opposing corners of the radiating element. This technique has been shown to introduce two, near-degenerate modes in the structure that – when excited in phase quadrature – combine to form circular polarization. The perturbations allow circular polarized operation with only a single feed point. The sense of the circular polarization is determined by the location of the feed point with respect to the perturbations. Both senses of circular polarization are excited by the introduction of orthogonal feeds for each of the two radiating elements. Thus, dual-ban, dual-circular polarization is obtained. The element achieves a low-profile from its printed circuit board realization. The high band square ring slot is realized in stripline. The orthogonal feeding transmission lines are printed on opposing sides of an electrically thin dielectric layer to allow them to cross without physically intersecting. This thin feeding substrate is sandwiched between two dielectric layers of matched dielectric constant. A ground plane is located on the top and bottom of the sandwiched dielectric structure, and the top ground plane contains the square ring slot with perturbed corners. Slotted stripline structures have been shown in the literature to excite a parallel-plate mode that can degrade overall performance of the antenna. Plated through holes are introduced at the outer perimeter of the square ring slot to short out this parallel-plate mode. The plated through holes (also called vias) serve as the shorting mechanism for the low band microstrip shorted square ring radiator. This element also contains triangular perturbations at opposing corners to excite circular polarization with a single feed point. In this element, orthogonal probe feeds are present to excite both senses of circular polarization. A dual-band, dual-polarized antenna element was built, tested, and compared to simulations. The constructed element operated at two distinct industrial, scientific, and medical (ISM) frequency bands due to their popularity in low power communications. The antenna element was realized in a multilayer printed circuit layout. A complex design procedure was developed and submitted to a printed circuit board company who manufactured the antenna element. The s-parameters of the antenna were measured using a Network Analyzer, and the results show good agreement with simulations. The radiation and polarization characteristics were measured in a compact range facility. These results also agreed well with simulations. The measured results verify the simulation models that were used in the simulations and establish a confidence level in the feasibility of constructing this element. The dual-band, dual-polarization nature of this element was established through the construction and measurement of this element. A novel size reduction technique was developed that allows for significant reduction of the element's footprint. This size reduction facilitates the placement of this element within an array environment. The loading technique utilizes a structure analogous to a parallel-plate capacitor to drastically reduce the overall size of the low frequency shorted square ring. The loading structure uses a substrate that is separate from that of the radiating elements. This allows the load to use a high dielectric material to achieve a high capacitance without requiring the radiating elements to be printed on high dielectric material that is potentially expensive and lossy at microwave frequencies. The two frequency bands were selected to be in separate industrial, scientific, and medical (ISM) bands. These frequency bands are increasingly popular in low power communication devices because unlicensed operation is permitted. The 2.45 GHz and 5.8 GHz ISM bands are commonly used for applications including Bluetooth technology, multiple 801.11 protocol, cellular phone technology, and cordless phones. The ISM bands were chosen for this antenna element due to their popularity, but this antenna is not restricted to these bands. The frequency ratio can be altered by controlling the dielectric constant used in the printed circuit board design, the parameters of the capacitive loading structure, and the size of the constituent elements that are used. After the size reduction technique is applied, the dual-band, dual-polarized elements can be placed in an array environment resulting in an array capable of generating both senses of circular polarization in the two, distinct ISM bands. This provides an aperture capable of supporting multiple functions. Depending on the applications required, the frequency bands of the antenna element can be altered to suit the particular system needs. The array analysis performed in this dissertation used a unique hybrid calculation technique that utilizes nine active element patterns to represent the patterns of the individual elements within a large antenna array. A common first look at array performance is achieved by multiplying the element pattern of an isolated element by an array factor containing the contributions of the geometrical arrangement of the antenna elements. This technique neglects mutual coupling between elements in the array that can alter the impedance match and radiation characteristics of the elements in the array. The active element pattern defines the radiation pattern of a given element in an array when all other elements are terminated in a matched impedance load. The active element pattern is unique for each element in an array. When these patterns are summed, the exact array pattern is obtained. While this technique has the advantage of accuracy, it is not ideal because it requires the simulation, calculation, or measurement of the pattern for each element in the array environment. The technique developed in this dissertation uses only nine active element patterns. These elements are then assigned to represent the active element patterns for all elements in the array depending on the geometrical region where the given element resides. This technique provides a compromise between the speed of using a single element pattern and the accuracy of using the unique active element pattern for each element in the array. The application of these two concentric, coplanar radiators along with the capacitive loading technique provides a unique contribution to the field of antenna engineering. The majority of dual-band antenna elements in the literature operate with a single polarization in each band. The ones that operate with dual-polarization in each band are typically limited to dual-linear polarization. Circular polarization is preferable to linear in many applications because it allows flexible orientation between the transmitting antenna and receiving antenna in a communications system, while also mitigating multipath effects that lead to signal fading. The ability to operate with two, orthogonal senses of circular polarization allows a system to reuse frequencies and double system capacity without requiring additional bandwidth. The uniqueness of this element lies in its ability to provide dual-circular polarization in two separate frequency bands for an individual element or an antenna array environment. The arrangement of the two element geometries with the addition of the novel capacitive loading technique is also unique. The performance of this element is achieved while maintaining the light weight, low profile design that is critical for many wireless communications applications. This dissertation provides a detailed description of the operation of this dual-band, dual-polarized antenna element. The design of the constituent elements is discussed for several polarization configurations to establish an understanding of the building blocks for this element. The dual-band, dual-polarized element is presented in detail to show the impedance match, isolation, and axial ratio performance. The capacitive loading technique is applied to the dual-band, dual-polarized element, and the performance with the loading in place is compared to the performance of the unloaded element. Next, there is an in-depth description of the array calculation technique that was developed to incorporate mutual coupling effects into the array calculations. This technique is then applied to the dual-band, dual-polarized array to show the performance of several array sizes. / Ph. D.

This thesis explores various Wi-Fi redundancy methods to enhance network resilience in industrial settings. Maintaining uninterrupted data transmission is crucial due to the increasing reliance on wireless technologies for industrial operations. Our research investigates the performance of different redundancy strategies, including Multi-Link Operation (MLO) and Truncated Automatic Repeat Request (TARQ), through practical prototyping and testing on specific hardware configurations. We aim to assess these methods' effectiveness in mitigating packet loss and improving transmission consistency under varying attenuation. The findings are expected to provide valuable insights into the potential of existing redundancy methods to improve Wi-Fi network robustness. This thesis evaluates two main redundancy methods: MLO and TARQ. In our findings, MLO demonstrated improved packet transmission consistency at lower levels of signal attenuation compared to standard implementations. TARQ, particularly on the 2.4 GHz band, significantly reduced packet loss across a wide range of attenuation levels, thus showing its potential to enhance network reliability.

Approved for public release, distribution is unlimited / In this thesis, a series of experiments were performed to characterize the material properties of InGaAs/GaAs for use in a two-color quantum-well IR photodetector (QWIP) design. Results from room temperature studies using cathodoluminescence and photoluminescence indicated light emission at 858 nm and 1019 nm from GaAs and InGaAs, respectively. Using a direct transport imaging technique, an edge dislocation pattern was observed and shown to be confined to the InGaAs layer of the material. A dislocation density measurement was performed and was shown to be less than 2000 lines/cm. Quantitative intensity level measurements indicated fluctuation in the region of dislocations to be less than 30% of the signal to background level. Finally, a spot mode study using the direct transport imaging method was performed to evaluate the feasibility of using this technique for contact-less diffusion length measurements. / Civilian, Department of Air Force

Nous proposons d'explorer dans le cadre de la thèse des solutions originales permettant d'obtenir des caractéristiques de rayonnement peu dépendantes du support de l'antenne. Les antennes étudiées et conçues visent à être utilisées pour des applications GNSS et plus précisément pour des applications multi-bandes du GNSS. Nous les développerons donc en respectant un cahier des charges associé. Deux axes de recherche indépendants sont explorés. Le premier montre les propriétés naturelles d'une antenne composée de plusieurs structures rayonnantes. Nous associons ainsi une structure hélicoïdale équivalente à un dipôle magnétique et un plan métallique équivalent à un dipôle électrique. La taille et les performances de l'antenne ainsi réalisée sont comparables par bien des aspects aux antennes que l'on trouve actuellement dans le commerce pour les applications GNSS. L'antenne réalisée est une antenne mono-bande en polarisation rectiligne ; ce qui n'est pas en accord avec les spécifications de l'application envisagée. Pour compléter cette première étude et satisfaire les exigences d'applications GNSS multi-bandes, nous nous orientons vers une autre technologie qui est exposé dans le second axe. Dans le second axe, nous associons une antenne électrique et un plan réflecteur particulier : une Surface Haute Impédance. L'association de ces deux éléments permet en théorie de réduire l'épaisseur qu'aurait un dispositif classique composé d'une antenne électrique et d'un plan réflecteur métallique. Nous commençons donc par étudier la particularité du plan réflecteur choisi, c'est-à-dire la Surface Haute Impédance. Cette surface étant composé de motifs périodiques nous étudierons le motif qui permet d'obtenir les caractéristiques les plus proches de celles de l'application visée. Nous débutons par une étude en monobande suivi de l'étude d'un motif bi-bande. Le motif mono-bande conçu en simulation présente une très bonne bande-passante (13%) au vue de sa taille minimale (2,5mm). Le motif bi-bande réalisé par imbrication de motifs mono-bande permet d'obtenir en simulation des performances conformes aux attentes dans deux bandes GNSS choisies. L'étude de cette surface se poursuit par une phase de mesure. Le but de l'étude étant de pouvoir placer une antenne au-dessus de la surface fabriquée, une collection d'antennes sera développée afin de régler la surface haute impédance et dans le même temps de tester le dispositif complet. Ainsi dans un premier temps, nous utiliserons des dipôles pour tester et régler la Surface Haute Impédance. Dans cette partie le couplage entre l'antenne et la surface haute impédance placée en-dessous sera notamment étudié. Dans un deuxième temps, afin d'obtenir une polarisation circulaire nous utiliserons d'autres antennes supportant cette polarisation (dipôle croisé et spirale). Dans chaque phase de mesure, le réglage antenne et Surface Haute Impédance sera optimisé et divers paramètres de réglage seront identifiés. Pour les deux axes de recherche, ce sont non seulement le rayonnement que nous cherchons à maîtriser mais aussi la taille de la structure. Ainsi les structures réalisées sont les plus compactes possibles surtout en terme de finesse. Nous concluons sur les performances des antennes réalisées par rapport au cahier des charges et aux autres antennes existantes et exposons les perspectives du travail réalisé / In this thesis, original solutions are proposed for antennas not sensitive to their environment. These antennas are designed for GNSS applications and more precisely for multi-bands ones. So the solutions are developed keeping in mind the GNSS specifications. Two different research axis are discussed. The first one deals with the natural properties of an antenna composed of different radiating structures. So an helix structure is associated with a metallic plate. The specifications of this antenna are in line with the ones of commercial antennas. Nevertheless, this antenna is only one band and in linear polarization which is not conform to the GNSS specifications. To satisfy these specifications a second axis is developed. In this second axis an electric antenna is associated with a specific reflector : a High Impendance Surface. Theorically, this surface allows to place the antenna very close and so reduce the thickness of the whole structure without disturbing the radiation of the antenna. Firstly, the High Impendance Surface and more precisely its periodic patterns is studied. Both one band and dual-band pattern are designed. The one band pattern has a good bandwidth (13%) compared to its size (2,5mm). The dual-band pattern designed by pattern enclosing realized the GNSS specifications in simulation. This is followed by measures. The aim of the thesis is to place the antenna above the designed HIS so a lot of antennas are designed to test and tune the surface. Firstly dipoles are used to study the coupling effects and secondly circular polarized antenna are used to reach the GNSS specifications. For both axis, the radiation pattern and the size of the whole system is optimized. So the proposed solutions are the thinnest ones. To conclude the characteristics of the proposed structures are compared to specifications and to existing antennas and future work is proposed

Les systèmes de télécommunications requièrent de plus en plus l’utilisation des composants passifs hyperfréquences. La commercialisation de ces composants nécessite la miniaturisation de leurs tailles, l’augmentation de leurs performances et la réduction de leurs coûts. Parmi ces composants passifs, nous citons le coupleur directionnel qui est un quadripôle destiné à répartir la puissance sur deux ports de sortie, le quatrième port reste isolé. Les travaux relatés dans ce manuscrit ont pour objectifs la conception et la réalisation d’un coupleur à accès coplanaires obtenu à partir d’un résonateur auquel nous avons appliqué des lignes de couplage. Un modèle équivalent approché a été mis en évidence par un logiciel de simulation circuit. Une étude paramétrique a été réalisée à l’aide d’un logiciel électromagnétique 3D pour fixer une règle de conception qui permet un dimensionnement convenable du composant pour un intervalle de fréquences prédéfinies. Un fonctionnement bi-bandes a été exploité pour chaque raccordement de la fréquence. Une deuxième structure de couplage a été déduite en reliant directement les lignes couplées sur le résonateur. Une étude paramétrique ainsi qu’une règle de conception ont mis en évidence un fonctionnement de coupleur mono-bande de cette structure à des fréquences prédéfinies. Une troisième structure qui fonctionne en coupleur a été exploitée en remplaçant le filtre résonateur par deux circuits en méandres. Ce nouveau coupleur à méandres présente des bandes passantes assez larges ainsi qu’un fonctionnement possible en bi-bandes. Ces coupleurs mis en œuvre peuvent assurer un couplage de l’ordre de 3 ; 6 ; 8 et 10 dB et d’un déphasage entre les deux ports de sortie de 180° pour les deux premières structures et de 90° pour le coupleur à méandres. Plusieurs séries de prototypes sont ensuite fabriquées à partir des structures optimisées en simulation. Les caractérisations hyperfréquences de ces composants montrent la performance des dispositifs réalisés / Telecommunications systems require more use of passive microwave components. The commercialization of these components requires the miniaturization of their size, increasing their performance and the reduction of their costs. Among these passive components we cited the directional coupler which is designated to spread the power between two outputs, the fourth port being isolated. The ambition of this work is to study and fabricate a coupler with coplanar access obtained from a resonator where we applied coupling lines. An equivalent approximate model was obtained using circuit simulation software. A parametric study was made using 3D electromagnetic software to fix a design rule that allows a suitable design for the component in a predefined frequency range. Dual-band operation has been exploited for each frequency. A second coupling structure was deduced by directly connecting the coupled lines to the resonator. A parametric study and a design rule have shown the operation of this structure as a single band coupler at predefined frequencies. A third structure which operates like a coupler has been exploited by replacing the resonator filter by two meandering circuits. This new meandering coupler presents a wide bandwidth and a possible operating in dual-band. These implemented couplers provided a coupling factor of 3, 6, 8 and 10 dB and a phase shift between the two output ports of 180° for the two first structures and a 90° phase shifter for the meandering coupler. Several sets of prototypes are then made. The microwave characterizations show the performance of the fabricated device

Les circulateurs à ferrite sont des dispositifs essentiels et indispensables dans les chaînes de communication radiofréquences. Ils assurent l’aiguillage des signaux selon leur provenance, en favorisant la propagation de l’onde EM dans une direction plutôt que dans une autre. De ce fait, ils permettent de dissocier les signaux d’émission et de réception. Ils utilisent les propriétés d’anisotropie et de non-réciprocité des matériaux ferrites lorsque ces derniers sont aimantés par un champ magnétique statique. Leur mise au point s’avère assez délicate. D’un point de vue industriel, pour répondre à un cahier des charges, sont souvent obligés aujourd’hui de partir de designs existants qu’ils font évoluer « au coup par coup » grâce au savoir-faire de quelques spécialistes. Des réglages longs, fastidieux, et coûteux sont donc nécessaires et ils ne garantissent pas toujours une solution optimum. Il est en outre souvent difficile d’imaginer de nouveaux designs. Le principal but de ces travaux de thèse est de mettre au point une méthode de conception fiable permettant de prendre en compte les phénomènes physiques mis en jeu (perméabilité tensorielle, effets magnétostatiques, modélisation numérique robuste) afin d’obtenir des dispositifs opérationnels, sans réglage et aux performances optimisées. / Biased ferrite circulators have known a great technological progress, searching for fulfill the exponential growth of many new applications. Their operation is directly linked to the anisotropic characteristic of ferrite material to create non-reciprocity phenomenon. Their design remains quite complicated in view of several limitations of their high-frequency modelization. The main goal of this thesis is to establish a complete methodology which aims to take into account all the physical features related to such a device, to offer a reliable results with optimized performances and to minimize the post-tuning step which remains problematic for the industry of circulators.

Capacitance-voltage-frequency measurements on n+-GaN/AlxGa1−xN UV/IR dual-band detectors are reported. The presence of shallow Si-donor, deep Si-donor, and C-donor/N-vacancy defect states were found to significantly alter the electrical characteristics of the detectors. The barrier Al fraction was found to change the position of the interface defect states relative to the Fermi level. The sample with Al fraction of 0.1 shows a distinct capacitance-step and hysteresis, which is attributed to C-donor/N-vacancy electron trap states located above the Fermi level (200 meV) at the heterointerface; whereas, the sample with Al fraction of 0.026 shows negative capacitance and dispersion, indicating C-donor/N-vacancy and deep Si-donor defect states located below the Fermi level (88 meV). When an i-GaN buffer layer was added to the structure, an anomalous high-frequency capacitance peak was observed and attributed to resonance scattering due to hybridization of localized Si-donor states in the band gap with conduction band states at the i-GaN/n+-GaN interface.

The objective of the proposed research is to develop simplified reconfigurable transmission systems with frequency multipliers for the transmission of complex modulated signals. Because they rely on nonlinear properties, frequency multiplier-based transmission systems require proper linearization techniques and accurate modeling of the signal transfer function. To accomplish these two goals, the author has developed techniques to model and linearize frequency multipliers and to digitize feedback signals for nonlinear characterization. First, adaptive predistortion techniques and zonal transfer theories have been developed for modeling and linearization. The predistortion system has been verified by applying an IS-95B signal to various frequency multipliers built by the author. Second, because the output signals at higher harmonic zones occupy wider frequency bandwidths than the signal in the fundamental zone does and thus make it harder to use traditional sampling techniques, a simplified but effective method called the sub-Nyquist sampling rate was developed and verified. Third, two methods for reconfigurable transmitters using frequency multipliers in conjunction with digital predistortion linearizers were developed. Both methods make it possible to transmit complex signals via frequency multipliers by using dual-band transmission systems that incorporate frequency multipliers that are based on linearization techniques. One of these methods uses a circuit topology that can be switched between a fundamental-mode in-phase combined amplifier and a push-push frequency doubler using input phasing. The second suggested method uses a fundamental-frequency power amplifier followed by a varactor multiplier that can be bypassed with an RF switch. This work will contribute to the development of low-cost and size-effective reconfigurable transmission systems because it requires fewer transmitting components and needs less sampling of the feedback networks.

Dual band (K and Ka) electronically scanning reflectarray with RF MEMS switches is designed, implemented and measured. Unit cell of the reflect array is composed of conductor backed split-ring elements. In order to steer the beam, the phase of the incident circularly polarized wave is controlled by RF MEMS switches that modify the angular orientation of split-rings individually. Reflectarray is designed using unit cell approach with periodic boundary conditions. The antenna is fabricated by using surface micromachining process developed in METU MEMS Center. Radiation patterns of the antenna are measured and compared with the simulations. It has been shown that the reflectarray is capable of beam switching to 35&deg / in Ka band, 24&deg / in K band.