Le milieu plasma correspond au 4ème état de la matière présentant une permittivité diélectrique complexe qui peut être exploitée pour les systèmes de communication. Sa permittivité négative a été étudiée dans de nombreux travaux de recherche démontrant que le plasma peut avoir des caractéristiques similaires à celles d'un métal en termes de conductivité électrique. En considérant une perméabilité positive, le plasma peut ainsi réagir de la même manière qu'un métal en présence d'une onde électromagnétique. Cette thèse a pour objectif de démontrer que le plasma est une alternative au métal pour la réalisation d'antennes reconfigurables. La première partie du travail concerne la caractérisation du milieu plasma en utilisant des sources plasma commerciales à savoir des lampes à Néon. Cette caractérisation est primordiale afin de pouvoir ensuite simuler ce type de source. La seconde partie des recherches a concerné la conception et la réalisation d'antennes plasma reconfigurables en rayonnement et ceci à la fréquence de 2.4 GHz. Le premier concept est un réflecteur circulaire et le second un réflecteur à angle droit tous les deux réalisés à partir de différentes lampes à Néon et illuminés par une antenne source monopole. Le réflecteur circulaire permet de dépointer le faisceau d'antennes sur 360° alors que le réflecteur à angle droit permet de reconfigurer le faisceau rayonnant et de passer d'un faisceau directif à deux faisceaux avec un creux dans l'axe. Ces dispositifs rayonnants innovants basés sur des lampes à Néon ont été validés expérimentalement et les résultats de mesure (S11 et rayonnement) sont en bonne adéquation avec les résultats de simulation. Ces deux types d'antennes réflecteurs possèdent également de bons résultats en termes de gain, ce qui valide l'utilisation et la caractérisation des lampes plasma de commerce utilisées. Dans la troisième partie du travail, ce même type de lampe à néon a été utilisé pour concevoir cette fois un élément rayonnant excité par couplage capacitif. La réalisation d'un prototype à permis de démontrer la faisabilité d'une telle source rayonnante. Enfin, la dernière partie des recherches concerne une étude de la Surface Equivalente Radar des antennes réflecteur conçues précédemment. L'étude a démontré que ces antennes réflecteurs plasma présentent des SER largement inférieures lorsqu'elles sont éteintes ainsi qu'à fréquence haute (8 GHz) comparativement à celles d'antennes métalliques équivalentes ce qui en fait des antennes furtives d'un point de vue radar. / Plasma is the 4th state of matter with complex permittivity that can be exploited to give advantages in communication system. Its negative permittivity has been studied in many research papers and it was proven to have similar characteristics as metal material in terms of electrical conductivity. While keeping permeability in the positive region, plasma will respond to electromagnetic waves in the similar manner as metal. Therefore, this thesis aimed to use plasma as an alternative to metal in the construction of reconfigurable antennas. The first part of this thesis is dedicated to characterize a plasma model based on the commercially available plasma source. Since there are many type of plasma source in terms of their electrical properties and physical shapes, it is important to characterize a particular plasma source so that it can be modeled in simulations to construct other types of plasma antennas. The second part presents the realization of plasma reflector antennas. Two types of plasma reflector antennas have been simulated, fabricated and measured at 2.4 GHz. The first one is are round reflector antenna (RRA) and the second one is corner reflector antenna (CRA). The performances of RRA have been validated and it was proven to provide beam shaping and beam scanning capability. The measured radiation patterns are in a good agreement with simulation ones. The capability of RRA is exceptional since it can steer its main beam from 0° up to 360°. Moreover, the scanning gain remains the same as the main beam is being moved from one direction to another. The CRA that has been introduced in this thesis is a novel design since it integrates two corner-reflector antennas on a single ground plane. The CRA offers three beam shapes which are electrically switchable from one shape to another. The CRA was simulated, fabricated and finally its performances were validated throughout a series of agile measurements. The measured reflected radiation patterns are in good agreements with the simulation ones. The measured gains of the RRA and CRA are 5 dB higher than the gain of classical monopole antenna with an identical size of finite ground plane. The fourth part deals with plasma as radio waves radiator. Two plasma antennas using commercially available U-shaped compact fluorescent lamp (CFL) have been fabricated and measured and it was proven that these antennas can be to radiate radio signal. The last part discusses about radar cross section performance of the plasma reflector antennas. The two plasma reflector antennas (RRA and CRA) were tested and measured for their RCS performance.

Le plasma est le quatrième état de la matière avec une permittivité complexe qui peut être exploitée pour donner des avantages aux systèmes de communications. Entre autres, une permittivité négative lui permet d'avoir des caractéristiques similaires aux matériaux métalliques en termes de conductivité électrique. Depuis de nombreuses années, les antennes plasma ont été étudiées en raison de leur capacité à être conductrices ou transparentes vis-à-vis des ondes électromagnétiques. Le principal avantage de l'utilisation d'antennes à base de plasma au lieu d'éléments métalliques est qu'elles permettent un contrôle électrique plutôt que mécanique. Par conséquent, cette thèse vise à utiliser le plasma comme une alternative au métal dans la construction des antennes reconfigurables. La première partie de cette thèse est consacrée à l'état de l'art sur l'utilisation du milieu plasma dans les systèmes de communications. Une lampe fluorescente spirale utilisée comme une cage de Faraday afin de protéger des antennes est présentée dans la deuxième partie. Deux types d'antennes (patch et monopôle) fonctionnant à 2,45 GHz sont placés à l'intérieur de cette lampe spirale. La troisième partie se focalise sur les réseaux d'antennes utilisant des tubes plasma pour reconfigurer l'ouverture du diagramme de rayonnement dans le plan H. Deux types de réseaux d'antennes sont étudiés : le premier est un réseau de patches imprimés et le second est un réseau d'antennes à fentes permettant de supporter des hautes puissances. La quatrième partie traite l'utilisation du plasma comme élément rayonnant. Deux antennes plasma (monopole et dipôle) utilisant une lampe fluorescente disponible dans le commerce ont été étudiées. Tous les systèmes antennaires présents dans cette thèse ont été simulés, fabriqués et mesurés. / Plasma is the 4th state of matter with complex permittivity that can be exploited to give advantages in communication systems. Its negative permittivity allows to have similar characteristics as metal material in terms of electrical conductivity. Since many years, plasma antennas have been studied due to their ability to be conductor or transparent for electromagnetic waves. The main advantage of using plasma antennas instead of metallic ones is that they allow electrical control rather than mechanical one. Therefore, this thesis aimed to use plasma as an alternative to metal in the design of reconfigurable antennas. The first part of this thesis is dedicated to the state of the art on plasma in communication systems in order to protect antennas. The second part presents the use of plasma spiral lamp as Faraday Shield effect. Two types of antennas (patch and monopole) operating at 2.45 GHz are placed inside this plasma spiral lamp. The third part discusses about reconfigurable antennas using plasma tubes and in order to reconfigure the half-power-beam-width of the radiation pattern in H plane. Two types of antenna array have been studied: The first one is a printed patches antenna array and the second one is a slotted antenna array allowing high power utilization. The fourth part deals with plasma as radiating element. Two plasma antennas using commercially available fluorescent lamp have been studied. All the antenna systems presented in this thesis have been simulated, manufactured and measured.

The plasma antennas offer a new solution to new requirements that are imposed on antenna systems with the advancing communication technology and increasing demand on wider frequency bands. In this thesis the plasma antennas are investigated for the radar and communication applications. The interaction of gas and semiconductor plasma with electromagnetic waves is inspected theoretically, and several experiments on the interaction of microwaves with gas plasma are conducted. Results of these experiments show that a relatively simple setup can produce plasma dense enough to interact with microwaves of frequency about 8 GHz. The previous studies of other institutes on plasma antennas are surveyed, emphasizing the results important for the use in radar and communication applications. Finally, semiconductor plasma is introduced, and an antenna system utilizing the semiconductor plasma generated by optical excitation is proposed.

Plasma is the 4th state of matter with complex permittivity that can be exploited to give advantages in communication system. Its negative permittivity has been studied in many research papers and it was proven to have similar characteristics as metal material in terms of electrical conductivity. While keeping permeability in the positive region, plasma will respond to electromagnetic waves in the similar manner as metal. Therefore, this thesis aimed to use plasma as an alternative to metal in the construction of reconfigurable antennas. The first part of this thesis is dedicated to characterize a plasma model based on the commercially available plasma source. Since there are many type of plasma source in terms of their electrical properties and physical shapes, it is important to characterize a particular plasma source so that it can be modeled in simulations to construct other types of plasma antennas. The second part presents the realization of plasma reflector antennas. Two types of plasma reflector antennas have been simulated, fabricated and measured at 2.4 GHz. The first one is are round reflector antenna (RRA) and the second one is corner reflector antenna (CRA). The performances of RRA have been validated and it was proven to provide beam shaping and beam scanning capability. The measured radiation patterns are in a good agreement with simulation ones. The capability of RRA is exceptional since it can steer its main beam from 0° up to 360°. Moreover, the scanning gain remains the same as the main beam is being moved from one direction to another. The CRA that has been introduced in this thesis is a novel design since it integrates two corner-reflector antennas on a single ground plane. The CRA offers three beam shapes which are electrically switchable from one shape to another. The CRA was simulated, fabricated and finally its performances were validated throughout a series of agile measurements. The measured reflected radiation patterns are in good agreements with the simulation ones. The measured gains of the RRA and CRA are 5 dB higher than the gain of classical monopole antenna with an identical size of finite ground plane. The fourth part deals with plasma as radio waves radiator. Two plasma antennas using commercially available U-shaped compact fluorescent lamp (CFL) have been fabricated and measured and it was proven that these antennas can be to radiate radio signal. The last part discusses about radar cross section performance of the plasma reflector antennas. The two plasma reflector antennas (RRA and CRA) were tested and measured for their RCS performance.

<p> In the past two decades, great interest in weakly ionized plasmas sustained by high voltage nanosecond pulsed plasmas at high repetition rates has emerged. For such plasmas, the electron number density does not significantly decay between pulses, unlike the electron temperature. Such conditions are favorable to reconfigurable plasma antennas where the low electron temperature may enable the reduction of the Johnson–Nyquist thermal noise if an antenna is operated in the plasma afterglow. Moreover, it may be possible to sustain such conditions with RF pulses. Doing so could enable a plasma antenna that transmits the driving frequency when the pulse is applied and receives other frequencies with low thermal noise between pulses.</p> <p>To study nanosecond pulsed plasmas, experiments were performed in a parallel-plate electrode configuration in argon and nitrogen gas at a pressure of several Torr and repetition frequencies of 30-75 kHz. To measure the time-resolved electron number density in the afterglow of each pulse, a custom 58.1 GHz homodyne microwave interferometer was constructed. The voltage and current measurements were made using a back current shunt (BCS). Initial analysis of the measured electron density in both plasmas indicated that the electron thermalization was much faster than the electron decay. In the nitrogen plasma, dissociative recombination with cluster ions was the dominant electron loss mechanism. However, the dissociative recombination rates of the electrons in the argon plasma suggested the presence of molecular impurities, such as water vapor. Therefore, to better understand the recombination mechanisms in argon plasma with trace amounts (0.1% or less by volume) of water vapor under the experimental conditions, a 0-D kinetic model was developed and fit to the experimental data. The influence of trace amounts of water on the electron temperature and density decay was studied by solving electron energy and continuity equations. It was found that in pure argon, Ar⁺ ions dominate while the electrons are very slow to thermalize and recombine. Including trace amounts of water impurities drastically reduces the time for electrons to thermalize and increases their rate of recombination. </p> <p>In addition to large quasi-steady electron number densities and low electron temperature in the plasma afterglow, plasmas sustained by nanosecond pulses use a lower power budget than those sustained by RF or DC supplies. The efficiency of the power budget can be characterized by measuring the ionization cost per electron, defined as the ratio of the energy deposited in a pulse to the total number of electrons created. This was experimentally determined in air and argon plasmas at 2-10 Torr sustained by 1-7 kV nanosecond pulses at repetition frequencies of 0.1-30 kHz. The number of electrons were determined from the measured electron density through microwave interferometry and assuming a plasma volume equivalent to the volume between electrodes. The energy deposited was calculated from voltage and current measurements using both a BCS as well as high frequency resistive voltage divider and fast current transformer (FCT). It was found that the ionization cost in all conditions was within a factor of three of Stoletov’s point (the theoretical minimum ionization cost) and two orders of magnitude less than RF plasma.</p><p> </p><p>Having shown that it is possible to generate high electron density, low electron temperature plasmas with nanosecond pulses, it was necessary to now create a plasma antenna prototype. Initially, commercial fluorescent light bulbs were used and ignited using surface wave excitation at various RF frequencies and powers. The S₁₁ of the antenna response was measured by a VNA through a novel coupling circuit, while the deposited power was measured using a bi-directional coupler. Next, a custom plasma antenna was created in which the pressure and gas composition could be varied. In addition to the S₁₁ and deposited power, the antenna gain, and the electron number density were also measured for a pure argon plasma antenna at pressures of 0.3-1 Torr. Varying the applied power shifts the antenna resonance frequency while increasing the excitation frequency caused an increase in measured electron density for the same deposited power. Initial tests using direct electrode excitation of a twin-tube integrated compact fluorescent light bulb with nanosecond pulses have successfully been achieved. Future efforts include designing the proper circuitry to time-gate out the large pulse voltage to facilitate safe antenna measurements in the plasma afterglow.<br></p>