Analysis and design of hybrid leaky-wave antennas loaded with frequency selective surfaces

[SPA] En esta tesis se propone una nueva antena de tipo Leaky-Wave (Leaky Wave Antenna, LWA). Estas antenas han recibido mucha atención en las últimas décadas por ser altamente directivas. En concreto, constituyen una solución especialmente atractiva para aplicaciones que requieran altas prestaciones y precisión, como en sistemas de comunicación por satélite y radar. Concretamente, las LWAs consideradas en esta tesis se basan en la radiación producida por una onda de fuga que se propaga por una cavidad resonante. Estas LWAs se denominan de tipo Fabry-Perot, por su analogía con los interferómetros. En concreto, se propone una nueva antena donde la cavidad Fabry-Perot se crea entre dos superficies selectivas en frecuencia (Frequency Selective Surface, FSS), una situada en la parte superior y que actúa como superficie parcialmente reflectante (Partially Reflective Surface, PRS) y otra situada en la parte inferior actuando como superficie de alta impedancia (High Impedance Surface, HIS). Debido a esta composición, denominamos la antena como PRS-HIS-LWA. Las dos FSS consisten en un sustrato dieléctrico impreso con parches metálicos. La principal ventaja de la nueva antena es que permite controlar las características de su diagrama de radiación de una forma flexible y precisa no conocida hasta la fecha. En el primer capítulo se describe la motivación de esta tesis, los objetivos planteados y se clarifican sus principales contribuciones originales. El segundo capítulo se centra en la caracterización eficiente de las superficies periódicas (FSS) que formarán parte de la PRS-HIS-LWA. Se trata de un paso clave, que permitirá el análisis y diseño de forma eficiente de la antena en su totalidad. Se proponen diversos métodos originales para la caracterización de FSSs, y se demuestra su alta eficiencia y utilidad no sólo en el marco de esta tesis, sino en el estudio de muchos otros dispositivos. En el tercer y cuarto capítulos se realiza el análisis y diseño de PRS-HIS-LWAs, comenzando por el caso de una estructura unidimensional (1D) y pasando después al bidimensional (2D). Ambas estructuras son interesantes desde el punto de vista práctico. Las antenas 1D son útiles para aplicaciones donde sea necesario escanear el punto del espacio hacia el que se dirige la radiación (escaneo del haz). Por otro lado, las 2D poseen la capacidad de apuntar hacia el cenit (broadside) con un lóbulo de radiación tipo lápiz muy directivo. El tercer capítulo de la tesis se centra en el análisis y diseño de PRS-HIS-LWAs 1D y 2D uniformes, es decir, en ellas la geometría de la PRS y la HIS permanece constante a lo largo de toda la antena. Se lleva a cabo el análisis de la PRS-HIS-LWA mediante el uso de una red equivalente transversa (Transverse Equivalent Network, TEN) en la que se incluyen las expresiones presentadas en el capítulo 2. Este análisis posibilita el estudio de la influencia de la geometría de la PRS y la HIS en el comportamiento de la antena. En concreto, se concluye que la PRS controla principalmente la tasa de radiación de la antena (y por lo tanto su ancho de haz) y que la HIS proporciona el control sobre ángulo de apuntamiento. En el capítulo cuarto se realiza la síntesis del diagrama de radiación de la PRS-HIS-LWAs tanto en el caso 1D como 2D. A partir de unos requerimientos del diagrama de radiación (ángulo de apuntamiento, ancho de haz, nivel de lóbulo principal a secundario, eficiencia de radiación, eficiencia de iluminación) se obtiene la tasa de radiación y ángulo de apuntamiento que debe presentar la antena en cada punto de su apertura radiante. Para obtener estas características es necesario utilizar los resultados obtenidos en el capítulo anterior y modular la geometría de la PRS y la HIS a lo largo de la estructura. De este modo se diseñan antenas no uniformes, o también llamadas “taper” donde la geometría de las superficies periódicas se ha modulado para sintetizar un determinado diagrama de radiación. Se propone una técnica sistemática totalmente novedosa para realizar esta síntesis, y se aplica en concreto en el caso de reducción de nivel de lóbulo principal a secundario en una antena 1D y en el caso de optimizar las eficiencias de radiación e iluminación en antenas 2D. En el quinto y último capítulo de esta tesis se presentan las conclusiones obtenidas del trabajo realizado así como las líneas futuras de investigación que sugiere. [ENG] This thesis proposes a new type antenna Leaky-Wave (Leaky Wave Antenna, LWA). These antennas have received much attention in the past decades to be highly directives. In particular, constitute an especially attractive solution for applications requiring high performance and precision, as in satellite communication systems and radar. Specifically, the Lwas considered in this thesis are based on the radiation produced by a leakage wave that propagates through a resonant cavity. These are referred Lwas Fabry-Perot type, by analogy with the interferometers. Specifically, it proposes a new antenna where Fabry-Perot cavity is created between two frequency selective surfaces (Frequency Selective Surface, HSS), one located at the top surface and serving as partially reflective (partially reflective surface, PRS) and one located on the bottom surface acting as a high impedance (High Impedance Surface, HIS). Because of this composition, called the antenna as PRS-HIS-LWA. The two FSS consist of a dielectric substrate with printed metallic patches. The main advantage of the new antenna is that it allows the characteristics of the radiation pattern of a flexible and precise unknown to date. The first chapter describes the motivation of this thesis, the objectives and clarified its main original contributions. The second chapter focuses on the efficient characterization of regular surfaces (FSS) that form part of the PRS-HIS-LWA. This is a key step that will allow the analysis and design of the antenna efficiently as a whole. Several methods are proposed to characterize original FSSS, and demonstrated its high efficiency and usefulness not only in the context of this thesis, but in the study of many other devices. In the third and fourth chapters of the study design and analysis of PRS-HIS-lwas, starting with the case of a one-dimensional structure (1D) and then moving to two-dimensional (2D). Both structures are interesting from a practical standpoint. 1D antennas are useful for applications where it is necessary to scan the space to the point that directs radiation (beam scanning). On the other hand, possess the ability 2D point toward the zenith (broadside) with a radiation lobe of highly directive pencil type. The third chapter of the thesis focuses on the analysis and design of PRS-HIS-1D and 2D Lwas uniform, ie, including the geometry of the PRS and HIS remains constant throughout the antenna. It carries out the analysis of the PRS-HIS-LWA using a network equivalent transverse (transverse Equivalent Network, TEN) which includes expressions presented in chapter 2. This analysis allows the study of the influence of the geometry of the PRS and the HIS antenna behavior. Specifically, it is concluded that the PRS mainly controls the rate of radiation of the antenna (and therefore its beamwidth) and which provides control over HIS pointing angle. The fourth chapter synthesis is performed radiation diagram of the PRS-HIS-Lwas both 1D and 2D case. From a radiation pattern requirements (pointing angle, beam width, main lobe level of secondary radiation efficiency, illumination efficiency) is obtained radiation rate and pointing angle of the antenna to be present in each radiant opening point. To obtain these characteristics it is necessary to use the results obtained in the previous chapter modular geometry HIS PRS and along the structure. Thus antennas are designed uniform, or so-called "taper" where the periodic surface geometry has been modulated to synthesize a particular radiation pattern. It proposes a completely novel technique for performing systematic this synthesis, and in particular applies in the case of reduction of main lobe level at an antenna side and in the case 1D optimize efficiencies in radiation and illumination 2D antennas. In the fifth and final chapter of this thesis presents the conclusions of the work and future lines of research that suggests.Universidad Politécnica de Cartagen

Analytical Design Procedures for the Odd Mode of Ridge Gap Waveguide Devices and Antennas

The millimeter-wave (mm-wave) band has attracted attention due to its wideband characteristics that make it able to support multi-gigabit per second data rate. Nevertheless, the performance of mm-wave wireless communication systems is restricted due to attenuation loss. Design of mm-wave components and antennas is rapidly growing with the current evolution in the wireless communication systems. However, the traditional waveguide structures such as microstrip, coplanar, substrate integrated waveguide, and rectangular waveguide either suffer from high losses or difficulty in manufacturing at mm-wave band. The ridge gap waveguide (RGW) technology is considered as a promising waveguide technology for the mm-wave band. RGW technology overcomes the conventional guiding structure problems as the wave propagates in an air gap region which eliminates the dielectric loss. Moreover, RGW does not need any electrical contacts, unlike traditional rectangular waveguides. Also, the RGW can be implemented in the printed form (PRGW) for easy integration with other planer system components. In this thesis, the use of the odd mode (TE10 (RGW)) RGW to design mm-wave components and antennas is presented. First, a systematic design methodology for the RGW using hybrid PEC/PMC waveguide approximation is presented. This reduces the design time using full wave simulators. The concept has been verified by simulation and experimental measurements. Second, two different methods to excite the odd mode in RGW are studied and investigated. In the first method, a planar L-shape RGW is used where less than -10 dB reflection coefficient is achieved, from 28 to 36 GHz, and more than 93% of the input power has been converted into the odd mode at the output port. The second method uses a magic tee with a shorted sum port and provides a wideband pure odd mode at the output port with reflection coefficient less than -10 dB from 28 GHz to 39 GHz. Other mm-wave components based on odd mode TE10 RGW are designed and presented including a Y-junction power divider and 3 dB forward coupler are designed for the first time in RGW technology. The Y-junction has a wideband matching from 28 to 34 GHz with a reflection coefficient less than -15 dB and the transmission output levels are about -3.3 dB. The usefulness of the odd mode RGW lies in the ability to increase the channel bandwidth that has been achieved by designing a dual-mode RGW. A magic tee is used to simultaneously excite the fundamental mode Q-TEM and the odd mode TE10 (RGW) on the ridgeline. The proposed dual-mode RGW performance is verified through simulation and measurement of a back-to-back configuration. The proposed design achieves a matching level less than -10 dB for the two modes over the frequency range from 29 GHz to 34.5 GHz with isolation better than 23 dB. The dual-mode RGW is then used to feed a reconfigurable Vivaldi horn antenna where two different radiation patterns can be obtained depending on the excited mode. The Q-TEM generates a single beam pattern, while the odd mode TE10 (RGW) generates a dual-beam pattern. The maximum gain for the single beam radiation is 12.1 dBi, while it is 10.43 dBi for the dual-beam pattern. The bandwidth of the dual-mode antenna is 25% at 32 GHz with impedance matching less than -10 dB and isolation better than 20 dB. Finally, several antennas are presented in this thesis based on the odd mode RGW. A novel differential feeding cavity antenna using the odd mode of RGW is presented. The measured results show good performance in terms of gain, bandwidth, sidelobe level, and cross-polarization. The maximum gain is 16.5 dBi, and the sidelobe level is -17 dB and -13.8 dB, for the E-plane and H-plane, respectively. Moreover, the proposed antenna has low cross-polarization levels of -35 dB in the E-plane and -27 dB in the H-plane. In addition, two 2x1 linear frequency scanning array antennas are designed and implemented using the proposed Y-junction to generate single beam and dual-beam patterns. The beam scan is from -11(degree) to -40(degree) at 28 GHz and 32 GHz, respectively

Aportación al estudio de antenas de lentes dieléctricas milimétricas

Escueal Técnica Superior de Ingeniería de Telecomunicació

New feeding networks and planar antenna designs for leaky-wave systems and communication applications

The fast development in modern communication systems such as radars, medical imaging, sensors or satellites demands efficient and compact antenna designs that can satisfy the high data throughput and beam scanning requirements. This is commonly achieved by different means including electromechanical or mechanical steering, which sometimes are not the best option as additional cost, size or losses may be introduced. However, low-cost and compact structures can be obtained by using planar leaky-wave antennas, whose inherent high directivity and electrical beam steering capabilities have been realised to be a solution for the issues encoun tered by these systems. Nevertheless, there are several limitations that these antennas still need to overcome. One clear example is the lack of efficient and simple feeding networks for certain types of leaky-wave antennas that can reduce their performance and compactness. In turn, there are modern indoor applications, such as WiFi or radio frequency identification (RFID), where selective distributed communications are required but current leaky-wave antennas cannot efficiently provide or their use implies cost and weight constraints. In this thesis, planar configurations are presented to provide efficient and low profile solutions for leaky-wave antennas using concepts such as partial reflective surfaces or simple technologies as parallel-plate waveguides. It is also demonstrated that novel systems for two-dimensional (2D) or wideband beam scanning can also be obtained by the use of simple feeders including vertical electric dipoles. In addition, a broad-beam alternative to a non-selective and expensive beam scanning performance inside airplanes for RFID systems is introduced easing weight restrictions. These configurations represent an advancement for the state-of-the-art and are interesting alternatives to their non-planar counterparts. To support these designs, theoretical analysis, full-wave simulations and measurements are provided

Advanced radiating systems based on leaky wave and nondiffracting waves

In recent years, microwave, millimeter-wave, and THz applications such as medical and security imaging, wireless power transfer, and near-field focusing, just to mention but a few, have gained much attention in the area of ICT due to their potentially high social impact. On one hand, the need of highly-directive THz sensors with tunable radiating features in the far-field region has recently boosted the research activity in the design of flexible, low-cost and low-profile devices. On the other hand, it is of paramount importance to focus energy in the near-field region, and thus the generation of limited-diffraction waves in the microwave and millimeter-wave regime is a topic of recent increasing interest. In this context, leaky-wave theory is an elegant and extremely useful formalism which allows for describing in a common fashion guiding and radiating phenomena in both the near field and the far field, spanning frequencies from microwaves to optics passing through THz. In this PhD thesis we aim to exploit the intrinsic versatility of the leakywave approach to design advanced radiating systems for controlling the far-field radiating features at THz frequencies and for focusing electromagnetic radiation in the near field at millimeter waves. Specifically, the use of relatively new materials such as graphene and liquid crystals has been considered for the design of leaky-wave based radiators, achieving very promising results in terms of reconfigurability, efficiency, and radiating capabilities. In this context, an original theoretical analysis has provided new general formulas for the evaluation of the radiating features (e.g., half-power beamwidth, sidelobe level, etc.) of leaky-wave antennas. Indeed, the current formulations are based on several simplifying hypotheses which do not allow for an accurate evaluation of the beamwidth in different situations. In addition to the intriguing reconfigurable capabilities offered by leaky waves in far-field applications, interesting focusing capabilities can be obtained in the near field. In particular, it is shown that leaky waves can profitably be used to generate limited-diffraction Bessel beams by means of narrow-band radiators in the microwave range. Also, the use of higher-order leaky-wave modes allows for achieving almost the same performance in the millimeter-wave range, where previous designs were subjected to severe fabrication issues. Even more interestingly, the limited-diffractive character of Bessel beams can also be used to generate limited-diffraction pulses as superpositions of monochromatic Bessel beams over a considerable fractional bandwidth. In this context, a novel theoretical framework has been developed to understand the practical limitations to efficiently generate limited-diffraction, limited-dispersion pulses, such as X-waves, in the microwave/millimeter-wave range. As a result of this investigation, a class of wideband radiators has been thoroughly analyzed, showing promising capabilities for the generation of both zeroth-order and higher-order Xwaves. The latter may pave the way for the first localized transmission of orbital angular momentum in the microwave range

Analysis and design of new electronically reconfigurable periodic leaky-wave antennas

[SPA] El principal objetivo de la tesis es el estudio de nuevas tecnologías en el campo de las antenas reconfigurables. En particular, la tesis se centra en explorar y explotar el potencial que presentan un tipo de antenas denominadas como ¿Antenas basadas en Modos de Fuga¿ para controlar electrónicamente su diagrama de radiación. La tesis desarrolla el análisis, diseño y fabricación de tres novedosas antenas basadas en modos de fuga capaces de variar mediante unas pocas señales de control y de forma continua su ángulo de apuntamiento. El mecanismo de reconfiguración electrónica principalmente se basa en el control de la dispersión de los modos de fuga excitados en dichas estructuras, mediante un control electrónico introducido empleando estructuras periódicas resonantes combinadas con elementos activos tales como diodos varactores. La tesis demuestra claramente la utilidad de estas antenas en el campo de la reconfiguración electrónica, proponiendo estas nuevas estructuras como alternativas a otras soluciones más clásicas (como antenas en array de fase reconfigurables o reflectores parabólicos mecánicamente re-orientables mecánicamente) y otras de actualidad (como reflectarrays, transmitarrays, antenas metamateriales o antenas pixeladas), las cuales todas ellas presentan otros problemas en términos de coste, complejidad de diseño o limitaciones de escalabilidad en frecuencia, aportando así esta tesis novedosos conceptos de reconfiguración electrónica.[ENG] The thesis aims the design of novel reconfigurable antennas with electronic beam-scanning. In particular, the antennas analyzed are known as Fabry-Perot Antennas (FPA) and are currently of high interest in the scientific community because of their high-directivity, low-profile and structure simplicity, what allow them to be an interesting alternative to other technologies (e.g. parabolic reflectors, phased arrays, etc.) which require of complex power distribution networks, bulky external sources or costly techniques to achieve reconfigurable capabilities. In this thesis, the integration of active components, such as varactor diodes, with FPRA structures, is exploited to achieve electronic control of their aperture illumination, which in turn results in the electronic steering of the radiation-pattern main beam. A modal analysis based on the leaky-wave theory has allowed to understand and predict the behavior of these structures. An equivalent circuit model was developed to design and optimize the dimensions of theses complex structures, saving computational cost and time. The antennas are based on the control of the frequency dispersion response and the electromagnetic band-gap (EBG) properties of periodic structures, employing specially designed Frequency-Selective Surfaces (FSS) loaded with varactor diodes. Three novel antenna prototypes were manufactured to demonstrate electronic steering capability operating at 5.5GHz. Continuous scanning in elevation (1D scanning) and also in elevation and azimuth simultaneously (2D scanning) have been achieved employing just a few control signals (between 1 and 4 signals). The antenna structures have been implemented in a low-cost technology based on parallel plate waveguides and printed circuit boards which have allowed to design antennas with a reduced profile. Theoretical, simulated and experimental results are shown for each prototype to demonstrate the concepts. Also, some future lines related to novel planar reconfigurable antennas in development are also outlined. One of the main potential advantages of the reconfiguring principles presented for future applications is their frequency scalability. This would allow to apply these concepts to other technologies, such as MEMS or graphene, to build new reconfigurable antennas able to operate at higher frequency bands (e.g. mm-bands) for future applications.Universidad Politécnica de Cartagen

A Millimeter-Wave Radar Microfabrication Technique and Its Application in Detection of Concealed Objects.

Millimeter-wave (MMW) radars are envisioned for a number of safety and security applications such as collision-avoidance, navigation and standoff target detection in all weather conditions. This work focuses on two MMW radar applications: (1) phenomenology of radar backscatter from the human body for the purpose of identification and detection of concealed objects on the body (2) microfabrication of advanced MMW radar to achieve compact and low-cost systems for autonomous navigation. In MMW band, the wavelength (1 mm ~ 1 cm) is long enough to allow signal penetration through cluttered atmosphere and clothing with little attenuation and short enough to allow for fabrication of small-size radar systems. Hence, this frequency band is well suited for the design of small sensors capable of obstacle detection and navigation in heavily cluttered environment and detecting hidden objects carried by individuals. For this purpose, a novel non-imaging approach is developed for distinction of walking human body and concealed carried object using polarimetric backscatter Doppler spectrum. This approach does not need radiometric calibration of the radar and preparation of the subject for radar interrogation. It is shown that a coherent polarimetric radar at W-band (95 GHz) or higher frequencies can be used for standoff detection of concealed carried objects. Motivated by these results, the thesis also includes an investigation on developing a technology for compact MMW radar systems. A micromachined, high-resolution, compact and low-power imaging MMW radar operating at 240 GHz intended for obstacle detection in complex environment is introduced. A frequency scanning antenna array micromachined from three layers of stacked silicon wafers is designed to provide 20 beamwidth in azimuth and 80 in elevation with azimuthal beam scanning range of ± 250. The frequency beam scanning is enabled by a meander rectangular waveguide with a slot array on its broad wall to feed linear microstrip patch antennas microfabricated on a suspended Parylene membrane. This technique offers high fabrication precision; provide easy fabrication and integration with active devices. The performances of the passive components of the radar system are verified using a WR-3 S-parameter and a near-field measurement systems.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91484/1/mvahid_1.pd

Magneto-dieletric properties of bismuth substituted barium hexaferrite

The work contained within this thesis seeks to address the dielectric and magnetic properties of bismuth substituted barium hexaferrite (composition BaBixFe12-xO19 where x = 0.0, 0.2, 0.5, 0.8, 1.0 and 1.5) across a broad frequency spectrum. This material is potentially of interest in antenna applications (specifically a dielectric resonator antenna) where high permittivity and permeability materials can be exploited to physically minimize the size of antenna devices. At low frequencies (20Hz - 3MHz) LCR meter based analysis was used to investigate the capacitance and inductance of the materials. The highest measured permittivity at 1MHz was Er = 86.18 - 9.910j, tanδ = 0.11. High frequency (45MHz - 20GHz) permittivity was investigated using a vector network analyser (VNA) and coaxial probe. The highest recorded permittivity at 2.45GHz was Er = 14.69 - 1.664j, tanδ = 0:08. A link between substitution level and permittivity and substitution level and inductance was made at either 1MHz or 2.45GHz. The homogeneity of the samples was explored using a near- field permittivity sensor. This showed small localized variations of permittivity across the surface but not significant enough to adversely effect bulk measurements. A dielectric resonator antenna was fabricated using a bismuth substituted barium hexaferrite sample. Resonant frequencies were identified at 6.6, 9.55 and 13.6GHz and radiation patterns for the system showed agreement with published theoretical results. This confirmed the suitability of the material in this application as a high permittivity material with relatively low loss. This thesis contributes to scientific knowledge by characterising a broad range of bismuth composition materials across a wide frequency range, investigating the link between permittivity/inductance and doping level and presenting full results. The material has also been characterised using a near-field permittivity technique and used to fabricated a dielectric resonator antenna which have not previously been undertaken

Energy: A continuing bibliography with indexes, issue 20

A bibliography is presented which lists 1250 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System from October 1, 1978 through December 31, 1978