Radio frequency interference (RFI) is undesired and commonplace. Using a subspace projection method to spatially remove the interference from a phased array system gives results of a 30 dB interference null rejection (INR). Unmanned systems have been developed to observe underwater activity and communicate their observations to passing aircraft. These systems are currently limited by their use of a single transmitter. The uplink can be improved by using a dual-antenna beam steering approach to maximize the signal-to-noise ratio (SNR) the aircraft receives. This approach demonstrates an increase in SNR of 3 dB when compared to a single transmitter.

The Electronically Steered Phased Array is one of the most versatile antennas used in radars applications. Some of the advantages of electronic steering are faster scan, no moving parts and higher reliability. However, the cost of phased arrays has always been prohibitive - in the order of $1M per square meter. The cost of a phased array is largely impacted by the cost of the high frequency electronics at each element and the cost of packaging. Advances in IC integration will allow incorporating multiple elements such as low noise amplifier, power amplifier, phase shifters and up/down-conversion into one or two ICs. Even though the cost for large quantities of ICs (both Silicon and GaAs) has lowered, the high cost of IC packaging and the array backplane still make the use of phase arrays for radar applications costly. The focus of this research is on techniques that reduce the packaging and the backplane cost of large electronically steered arrays. These techniques are based on simplified signal distributions schemes, reduction of layers in the backplane and use of inexpensive materials. Two architectures designed based on these techniques, as well as a novel BGA active antenna package for dual polarized phased arrays are presented. The first architecture, called the series fed row-column architecture, focuses on the reduction of phase shifters and control signals used in the backplane of the array. The second architecture, called the parallel plate feed architecture, is based on a simplified scheme for distribution of the local oscillator signal. A prototype making use of each one of these architectures is presented. Analysis of advantages and disadvantages of each of these architectures is described. The necessity of cost reduction is a factor that can possibly impact the polarization performance of the antenna. This factor is a motivation to study and develop calibration techniques that reduce the cross-polarization of electronically steered phased arrays. Advances on Interleaving Sparse Arrays, a beam forming technique for polarization improvement/correction in phased arrays, are also presented.

No description available.

No description available.

Dès lors que des éléments rayonnants sont placés à proximité les uns des autres, comme c'est le cas au sein des antennes réseaux à balayage électronique, des interactions électromagnétiques parasites se créent entre eux. Ces couplages se manifestent par une perturbation des répartitions de courants des sources du réseau. Leur impact dépend fortement de l'angle de dépointage du réseau mais est généralement néfaste, car ils modifient les caractéristiques du rayonnement des sources. Les différents objectifs de compacité et les spécifications de performances radioélectriques visés pour les radars aéroportées peuvent conduire à des structures qui supportent et favorisent ces phénomènes de couplages parasites, sous la forme d’ondes d’espace et de surface. Ces derniers peuvent aller jusqu'à entrainer l'impossibilité pour l'antenne de rayonner dans certaines directions et à certaines fréquences d’utilisation : on parle de directions aveugles. Ce phénomène limite de manière considérable le volume de dépointage opérationnel d'un système radar. La maîtrise du couplage entre les éléments rayonnants est donc l'une des problématiques essentielles du développement et du dimensionnement d'une antenne réseau. La recherche qui traite de ce sujet n'en est plus à ses débuts (les premiers radars à balayage électronique sont exploités depuis les années 50) mais reste toujours en attente de solutions innovantes permettant de mieux comprendre et maîtriser ces phénomènes. Dans cette thèse, plusieurs méthodes permettant de minimiser les effets du couplage dans les réseaux à balayage électroniques ont été investiguées. Les travaux s'orientent notamment autour du défi de réduire les conséquences des directions aveugles sans modifier la maille initiale du réseau d'antenne (contrainte iso-maille). / When radiating elements are located close to one another, as it is the case in electronically phased array antennas, parasitic electromagnetic interferences occur between them. The impact of these coupling mechanisms depends to a large extent on the scanning angle of the array, but is usually harmful, since it alters the radiating properties and the active input impedance of the sources. The compactness objectives and radioelectric performances required for airborne radars can lead to structures that support and foster these parasitic couplings, in the form of surface or space waves. In some cases, mutual coupling can even result in the impossibility for the array to radiate in certain directions and at certain frequencies. This phenomenon, referred to as scan blindness, significantly reduces the operating scan volume of a radar system. In that respect, the control of coupling mechanisms between radiating elements is a major issue when developing an array antenna and although the research that deals with this subject is no longer in its infancy, it is always pending for new and innovating solutions to master these phenomena. In this thesis, different solutions enabling to minimize the effect of couplings in phased arrays are investigated. The presented research revolves around the challenge of limiting scan blindness consequences without modifying the initial mesh of the array antenna.

Mobile communication has become an essential part of our daily life. We love the flexibility of wireless cell phones and even accept their lower quality of service when compared to wired links. Similarly, we are looking forward to the day that we can continue watching our favorite TV programs while travelling anywhere and everywhere. Mobility, flexibility, and portability are the themes of the next generation communication. Motivated and fascinated by such technology breakthroughs, this effort is geared towards enhancing the quality of wireless services and bringing mobile satellite reception one step closer to the market. Meanwhile, phased array antennas are vital components for RADAR applications where the antenna is required to have certain scan capabilities. One of the main concerns in that perspective is how to avoid the potential of scan blindness in the required scan range. Targeting to achieve wide-band wide-scan angle phased arrays free from any scan blindness our efforts is also geared. Conventionally, the key to lower the profile of the antenna is to use planar structures. In that perspective microstrip patch antennas have drawn the attention of antenna engineers since the 1970s due to their attractive features of being low profile, compact size, light weight, and amenable to low-cost PCB fabrication processes. However, patch elements are basically resonating at a single frequency, typically have <2% bandwidth, which is a major deficit that impedes their usage in relatively wide-band applications. There are various approaches to enhance the patch antennas bandwidth including suspended substrates, multi-stack patches, and metalized cavities backing these patches. Metalized cavity-backed patch structures have been demonstrated to give the best performance, however, they are very expensive to manufacture. In this dissertation, we develop an alternative low-cost bandwidth enhancement topology. The proposed topology is based on substrate-integrated waveguides. The great potential of the proposed structure lies in being amenable to the conventional PCB fabrication. Moreover, substrate-integrated cavity-backed structures facilitate the design of sophisticated arrays that are very expensive to develop using the conventional metalized cavity-backed topology, which includes the common broadside arrays used in fixed-beam applications and the scanned phased arrays used in RADAR applications.

L’objectif de cette thèse était de concevoir, fabriquer, et tester des transducteurs ultrasonores multi – éléments pour des applications en environnements sévères. Dans ce contexte, des techniques de caractérisation des matériaux ont été développées afin d’adapter la conception des transducteurs en fonction des contraintes de l’environnement, et plus particulièrement la température. Deux types de conceptions ont été étudiées selon les applications visées : La première application consistait à développer un transducteur ultrasonore permettant de réaliser des contrôles non destructifs dans des réacteurs de génération IV (refroidi au sodium liquide) lors d’un arrêt de tranche. Dans ce cas, l’environnement sévère était caractérisé par une température de 200 °C, et la présence de sodium liquide. Des radiations pouvaient également être présentes. Pour cette application, un transducteur (nommé LiNa) sous la forme d’un projecteur ultrasonore linéaire de 20 éléments, fonctionnant à 2.5MHz a été fabriquée, puis testé en eau et en sodium liquide. La seconde application consistait à développer un transducteur ultrasonore permettant de réaliser des contrôles non destructifs en contact de pièces massives en cours de soudage. Une pièce massive est par exemple une cuve de réacteur nucléaire. Ce transducteur permet de détecter des défauts dans une soudure très rapidement après sa réalisation, et ainsi corriger directement cette dernière, sans attendre que les pièces soient refroidies. Pourcette application, un transducteur (nommé MaCo) sous forme de matrice 8 × 8 éléments, fonctionnant à 5MHz a été développé, et caractérisé de la température ambiante, jusqu’à 240 °C. Avec ce capteur, Avec ce capteur, des échos en ondes transversales ont été obtenus jusqu’à la température limite, sans refroidissement. / The goal of this thesis was to design, fabricate and test phased arrays ultrasonic transducers for harshenvironment applications. In this context, characterization methods were developed in order to adapt transducerdesign to the environment. We designed two types of ultrasonic phased array transducers according to theconsidered application:The first application aimed at developping an ultrasonic transducer for non destructive testing in IVth generationnuclear reactors (cooled with liquid sodium) during reactor outages. In this case, the harsh environment wascharacterized by a temperature of 200 °C, and the presence of liquid sodium. Radiations could also be present.For this application, a 20 elements 2.5MHz immersion linear projector (called LiNa) was fabricated then testedunder water and under liquid sodium.The second application aimed at developping an ultrasonic transducer in order to realize non destructive testingin contact with massive pieces during welding. A massive piece for example is a tank for nuclear plant reactor.The transducer will permit to quickly detect defects in a weld after its realization, and then correct it directlyif necessary, without waiting for the pieces to cool down at ambient temperatures. For this application,a 64elements 5MHz matrix transducer (named MaCo) were developed and tested from ambient to 240 °C. Thetransducer worked up to the limit temperature without any cooling system, and some typical defects weredetected.

Weather monitoring and forecasting systems have witnessed rapid advancement in recent years. However, one of the main challenges faced by these systems is poor coverage in lower atmospheric regions due to earth's curvature. The Engineering Research Center for the Collaborative Adaptive Sensing of the Atmosphere (CASA) has developed a dense network of small low-power radars to improve the coverage of weather sensing systems. Traditional, mechanically-scanned antennas used in these radars are now being replaced with high-performance electronically-scanned phased-arrays. Phased-Array radars, however, require large number of active microwave components to scan electronically in both the azimuth and elevation planes, thus significantly increasing the cost of the entire radar system. To address this issue, CASA has designed a "Phase-Tilt" radar, that scans electronically in azimuth and mechanically in elevation. One of the core components of this system is the Phased-Array controller or the Array Formatter. The Array Formatter is a Field Programmable Gate Array (FPGA)-based master controller that translates user commands from a computer to control and timing signals for the radar system. The objective of this thesis is to design and test an FPGA-based Array Formatter for CASA's Phase-Tilt radar system.

This work continues the development of phased array radar for UAS detection and tracking. The earlier 1D scanning, 4 channel BYU SAA radar is improved upon and replicated to form a network of radars. These are shown to work together for higher level tracking across multiple fields of view. Additionally, a new phased array instrument is designed and constructed with 16 channels, 2D scanning, and improved signal processing algorithms. Preliminary metrics and field results show the operation of this sensor. A new technique for measuring array mutual impedances from embedded element patterns is developed here. This technique uses an antenna range instead of a network analyzer. New mathematical relationships are built to handle cases for practical measurements and field transformations. Demonstration of this method with a 2x2 uniform rectangular array is shown and compares favorably with the mutual impedances traditionally measured with a network analyzer. A new way to measure radiation efficiency using the antenna Y factor method is demonstrated. This method does not require an expensive field measurement chamber and can be done with a simple ground shield and absorber foam. Various X band antennas have their radiation efficiency characterized and compare favorable with known efficiencies.

No description available.