Direction Finding With Mutually Orthogonal Antennas

Estimating the direction-of-arrival of incident electromagnetic plane waves (a.k.a. direction finding or DF) has typically been accomplished in the past using arrays of spatially separated antennas. The spatial separation produces a delay in each antenna\u27s measured voltage due to the finite propagation time as the wave strikes each antenna in succession. In this thesis, we approach the problem differently by using three antennas that have been oriented in orthogonal directions but are co-located at the origin of a coordinate system. Being co-located, this mutually orthogonal arrangement of antennas cannot detect the propagation phase delay and must rely solely on the polarization properties of the incident waves. Using the vector effective height concept, three algorithms are formulated. The first algorithm estimates the direction-of-arrival by computing a vector that is perpendicular to the locus of the instantaneous electric field vector. The second and third algorithms are based on the well-known maximum likelihood and MUSIC algorithms. Simulation results show that each algorithm can estimate the direction-of-arrival with a root-mean-squared error within 1° or less when the incident wave is circularly polarized, the antennas are small compared to wavelength, and the signal-to-noise ratio is above 20dB

Design and Analysis of a Cylindrical Dielectric Resonator Antenna Array and Its Feed Network

There is an ever increasing need for smaller, lighter, more efficient antennas for commercial and military applications. One such antenna that meets these requirements is the dielectric resonator antenna (DRA). In recent years there has been an abundance of research on the utilization of the DRA as a radiating element. However, its practical application - especially pertaining to DRA arrays - is still considered to be at its infancy. The purpose of this work is to present a systematic process to be used in the design, simulation, optimization, fabrication, and testing of a cylindrical DRA array including its associated feed network. The DRA array development cycle begins with a single cylindrical radiating element. ComDRA parameters such as DRA radius, feed type, feed location, and element spacing are investigated. A DRA element in this research is optimized for bandwidth and gain for use at x-band (8-12 GHz). The antenna feed network, being an integral part of all antenna arrays, is also considered. The primary causes of impedance mismatch in the feed network are identified and techniques to improve performance are explored. An improvement in impedance bandwidth is gained through traditional transmission line matching methods. Ultimately, a 16 (4x4) element and 256 (16x16) element array is fabricated, tested, and compared to an existing commercial technology

Mutual coupling studies in stacked waveguide slot arrays

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1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

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

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Polarizable Particles and their Two-Dimensional Arrays: Advances in Small Antenna and Metasurface Technologies.

Metamaterials are subwavelength-structured materials designed to exhibit tailored electromagnetic properties. Metamaterials have allowed extreme control over constituent material parameters (i.e. permittivity, permeability, and chirality), which has enabled a myriad of counterintuitive physical phenomena. However, metamaterials typically suffer from high losses, difficulties in fabrication, and are bulky. This has led to the development of metasurfaces, which are the two dimensional equivalent of metamaterials. Metasurfaces can impart abrupt discontinuities on electromagnetic wavefronts, allowing electromagnetic fields to be tailored across subwavelength length scales. The building blocks of metasurfaces are subwavelength textured, polarizable particles. Near resonance, these particles support strong currents, which makes them excellent small antennas. In this thesis, a circuit model is developed that can model an arbitrary small antenna based on its frequency dependent polarizability. In addition, a direct transfer patterning process is developed that allows metallic patterns to be printed onto arbitrarily contoured substrates. This work will find immediate applications in a number of emerging technologies resulting from the rapid expansion of the mobile electronics industry. Next, extreme control of the polarization and profile of a wavefront is demonstrated using two-dimensional arrays of polarizable particles (i.e. metasurfaces). A new class of metasurfaces, referred to as metamaterial Huygens' surfaces, is shown to have a significantly improved efficiency over the state of the art. Metamaterial Huygens' surfaces utilize polarizable particles that exhibit both an electric and magnetic response, which allows for reflectionless wavefront control. Next, it is shown that simply cascading patterned metallic sheets can also provide high transmission and complete phase control. To demonstrate the design methodology, several different metasurfaces are developed that deflect incident Gaussian beams to a stipulated angle or convert an incident Gaussian beam into a vector Bessel beam. Further, utilizing sheets with anisotropic patterns provides additional magneto-electric coupling, which enables complete control of a wavefront (i.e. amplitude, phase, and polarization control). The experimental verification at frequencies ranging from microwaves to optics highlights the versatility of this work.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111395/1/carlpfei_1.pd