Design and Analysis of Circularly Polarized Electrically Small Antennas

A growing need for efficient wireless communication is prevalent in the world in which we live. From cell phones to television to GPS applications, wireless communications are vital in consumer electronics and military applications. In these applications, a miniaturized antenna is sometimes necessary for reducing overall size of the communication system. For many satellite based communication applications, circular polarization in antennas is needed for efficient communication. In this thesis, the miniaturization technique known as T-top loading is utilized on two novel antenna designs. One design is an electrically small, circularly polarized planar cross dipole and the other design is a compact circularly polarized log-periodic dipole array. Both antennas are designed in simulation software with the intent for prototype fabrication for measurement verification of simulation results

Antenna Systems for Wideband Direction Finding and Spectrum Sensing

Antenna systems for direction finding (DF) and spectrum sensing remain vital to modern engineering; civilian and defense sensing requires wideband systems meeting rigorous requirements across the spectrum. Wideband DF systems can be examined as wide absolute bandwidth or wide relative bandwidth. The challenges at mm-wave frequencies are the large impact of small features and controlling pattern shape over wide absolute (>30GHz) bandwidths. At microwave frequencies the challenge is establishing ripple-free beam shape over wide relative (>3:1) bandwidth. Typical DF at high frequencies uses poorly controlled pattern shape, while at low frequencies allow low efficiencies and strong pattern ripple, reducing accuracy and range. More rigorous goals require analytical evaluation of DF antennas, and pattern and mode control. A theory is developed analyzing DF with ideal cosine, sinc, or gaussian radiation patterns. This theory models many realistic antenna beams, and shows a fundamental link between beam shape and pointing angle, and three DF system parameters: field of view (FOV), minimum FOV gain, and minimum DF function slope. Utilizing this framework, realistic system goals are established, antennas can be evaluated analytically, guiding design for DF. This analysis is validated by design of three antennas. A curved aperture horn is designed for wide absolute bandwidth W-band Sensing, and substantial pattern control over frequency, enabling frequency insensitive DF. Multiple manufactured configurations show agreement with simulation. A dual polarized TEM horn is developed for wide relative bandwidth L to C-band operation, integrated with loop and bowtie antennas to achieve miniaturization through spherical modes engineering. High efficiency, dual polarization, and DF operation are obtained. Measurements show agreement of pattern shape and validate design, but are impacted by modeled and actual absorber loss. A dual polarized LPDA antenna is designed from L to C-band for consistent gain and match. Development includes integrated tapered line matching network. Performance impacts of geometric parameters are discussed. Finally, 3D Printing is investigated for self-supporting, low-loss coaxial lines. A High Q resonator is designed to investigate surface roughness. Wideband filters and diplexers are demonstrated, incorporating novel coaxial junction geometry to compensate for parasitic loading. Manufactured devices achieve significant miniaturization and agreement with simulation

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

UWB Technology

Ultra Wide Band (UWB) technology has attracted increasing interest and there is a growing demand for UWB for several applications and scenarios. The unlicensed use of the UWB spectrum has been regulated by the Federal Communications Commission (FCC) since the early 2000s. The main concern in designing UWB circuits is to consider the assigned bandwidth and the low power permitted for transmission. This makes UWB circuit design a challenging mission in today's community. Various circuit designs and system implementations are published in this book to give the reader a glimpse of the state-of-the-art examples in this field. The book starts at the circuit level design of major UWB elements such as filters, antennas, and amplifiers; and ends with the complete system implementation using such modules

Synthetic aperture radar-based techniques and reconfigurable antenna design for microwave imaging of layered structures

In the past several decades, a number of microwave imaging techniques have been developed for detecting embedded objects (targets) in a homogeneous media. New applications such as nondestructive testing of layered composite structures, through-wall and medical imaging require more advanced imaging systems and image reconstruction algorithms (post-processing) suitable for imaging inhomogeneous (i.e., layered) media. Currently-available imaging algorithms are not always robust, easy to implement, and fast. Synthetic aperture radar (SAR) techniques are some of the more prominent approaches for image reconstruction when considering low loss and homogeneous media. To address limitations of SAR imaging, when interested in imaging an embedded object in an inhomogeneous media with loss, two different methods are introduced, namely; modified piecewise SAR (MPW-SAR) and Wiener filter-based layered SAR (WL-SAR). From imaging system hardware point-of-view, microwave imaging systems require suitable antennas for signal transmission and data collection. A reconfigurable antenna which its characteristics can be dynamically changed provide significant flexibility in terms of beam-forming, reduction in unwanted noise and multiplicity of use including for imaging applications. However, despite these potentially advantageous characteristics, the field of reconfigurable antenna design is fairly new and there is not a methodical design procedure. This issue is addressed by introducing an organized design method for a reconfigurable antenna capable of operating in several distinct frequency bands. The design constraints (e.g., size and gain) can also be included. Based on this method, a novel reconfigurable coplanar waveguide-fed slot antenna is designed to cover several different frequency bands while keeping the antenna size as small as possible --Abstract, page iii

Radar Sub-surface Sensing for Mapping the Extent of Hydraulic Fractures and for Monitoring Lake Ice and Design of Some Novel Antennas.

Hydraulic fracturing, which is a fast-developing well-stimulation technique, has greatly expanded oil and natural gas production in the United States. As the use of hydraulic fracturing has grown, concerns about its environmental impacts have also increased. A sub-surface imaging radar that can detect the extent of hydraulic fractures is highly demanded, but existing radar designs cannot meet the requirement of penetration range on the order of kilometers due to the exorbitant propagation loss in the ground. In the thesis, a medium frequency (MF) band sub-surface radar sensing system is proposed to extend the detectable range to kilometers in rock layers. Algorithms for cross-hole and single-hole configurations are developed based on simulations using point targets and realistic fractured rock models. A super-miniaturized borehole antenna and its feeding network are also designed for this radar system. Also application of imaging radars for sub-surface sensing frozen lakes at Arctic regions is investigated. The scattering mechanism is the key point to understand the radar data and to extract useful information. To explore this topic, a full-wave simulation model to analyze lake ice scattering phenomenology that includes columnar air bubbles is presented. Based on this model, the scattering mechanism from the rough ice/water interface and columnar air bubbles in the ice at C band is addressed and concludes that the roughness at the interface between ice and water is the dominate contributor to backscatter and once the lake is completely frozen the backscatter diminishes significantly. Radar remote sensing systems often require high-performance antennas with special specifications. Besides the borehole antenna for MF band subsurface imaging system, several other antennas are also designed for potential radar systems. Surface-to-borehole setup is an alternative configuration for subsurface imaging system, which requires a miniaturized planar antenna placed on the surface. Such antenna is developed with using artificial electromagnetic materials for size reduction. Furthermore, circularly polarized (CP) waveform can be used for imaging system and omnidirectional CP antenna is needed. Thus, a low-profile planar azimuthal omnidirectional CP antenna with gain of 1dB and bandwidth of 40MHz is designed at 2.4GHz by combining a novel slot antenna and a PIFA antenna.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120674/1/wujf_1.pd

Diseño de un arreglo de antenas Log-Periódicas para la banda de onda milimétrica

El presente artículo detalla el diseño, simulación y comparación entre un arreglo de antenas log-periódicas (LPDA) lineales 2x1, 3x1 y un arreglo matricial 2x2, que operan en la banda de ondas milimétricas (mmW) a una frecuencia de resonancia de 60 GHz. Con la finalidad de mejorar sus características se modela los distintos arreglos, que consisten en antenas idénticas, orientadas de forma simétrica equidistante. Estos modelos se derivan a partir del esquema base que se implanta mediante la ejecución de los principios básicos de la estructura de una antena log-periódica y la experimentación de sus diferentes materiales aislantes y conductores. Los arreglos son simulados a través del software ANSYS HFSS. Por consiguiente, se realizó un análisis comparativo donde se verificó el impacto que presenta uno frente a otro, en el cual se logró determinar que al incrementar el número de antenas de carácter lineal y matricial produce un aumento de la ganancia, por esta razón, se obtiene patrones de radiación sumamente directivos, donde el más destacado en cuanto a sus parámetros de dispersión posee una frecuencia de 60 GHz, coeficiente de reflexión (S11) igual a -23.79 dB, VSWR= 1.12 y un patrón de radiación directivo con ganancia máxima de 10.51 dB.This article details the design, simulation and comparison between a 2x1, 3x1 linear log-periodic antenna array (LPDA) and a 2x2 matrix array, operating in the millimeter wave (mmW) band at a resonance frequency of 60 GHz. In order to improve its characteristics, the different arrangements are modeled, which consist of identical antennas, oriented in an equidistant symmetric way. These models are derived from the basic scheme that is implemented through the execution of the basic principles of the structure of a log-periodic antenna and the experimentation of its different insulating and conducting materials. The arrays are simulated through ANSYS HFSS software. Consequently, a comparative analysis was carried out where the impact presented by one against the other was verified, in which it was determined that increasing the number of linear and matrix antennas produces an increase in gain, for this reason, obtains highly directive radiation patterns, where the most outstanding in terms of its dispersion parameters has a frequency of 60 GHz, reflection coefficient (S11) equal to -23.79 dB, VSWR= 1.12 and a directive radiation pattern with maximum gain of 10.51 dB

Multifunction Radio Frequency Composite Structures

There has been recent interest in the development of multifunction structures for weight-critical applications. A multifunction structure is a load-bearing structure that also allows one or more additional functions such as RF communication, energy storage, sensing etc. The focus of this dissertation is to analyze, design, develop, and test new high performance (broadband, high gain, circularly polarized) internal antennas that are structural and integral to the aircraft. It is demonstrated that antennas with more bandwidth and higher efficiency could be developed if the space and materials available in an aircraft structure could be judiciously exploited for multifunctional usage. This is improbable with bolt-on approaches, such blade antennas or antennas housed within a wing pod. Firstly, a method called Characteristic Mode Analysis (CMA) is studied and used both for a dipole antenna and a VHF airfoil integrated antenna. Although computationally intensive, it provides fundamental insights on the significance of each mode, modal interactions, and overall achievable bandwidth. The CMA of a dipole antenna loaded with a thin coating of DNG material is undertaken. The presented analysis considers the MoM Galerkin formulation. The analyses presented demonstrate that when the relative permittivity and permeability are greater than -1 but less than 0, the configuration shows potential for antenna size reduction. For example, a 25% size reduction is achieved when the relative permittivity and permeability are equal to -0.3. Secondly, the study, design, and development of a broadband (2:1 frequency ratio), positive gain (\u3e 0 dBi), VHF antenna integrated within a composite airfoil structure are undertaken to overcome the limitations of very low gain (-20 dBi typical at low VHF frequencies) associated with resistively matched, electrically small, broadband airborne blade antennas. It is demonstrated that a broadband antenna operating from 89-220 MHz can be incorporated into composite structures. Simulation and experimental results clearly show that such antennas can be built using structural composite materials, such as fiberglass or cyanate-ester/quartz, Rohacell foam and conductive mesh with appropriate thicknesses commensurate with the frequency band of operation. Additionally, the antenna is studied with CMA to understand the contributions of various modes to antenna performance and to asses the performance impact of composite materials as a result of structural integration. The proposed sandwich structure antenna was also studied for possible MIMO application in an inverted V-tail UAV configuration. The two antennas in that configuration clearly show excellent performance based on their ECC and simulated radiation patterns. Finally, fundamental studies and innovations are made in the topic area of structurally integrated, broadband, circularly polarized spiral antennas on EBG structures. To allow directional radiation, spirals require a quarter of a wavelength separation when placed on a reflecting surface (e.g. the aircraft’s ground). This thickness (as much as 6 inches or more at 450 MHz) is a significant challenge from a structural integration perspective and is unacceptable at UHF frequencies. While RF absorbing materials have been proposed, they significantly reduce antenna efficiency. To our knowledge, no work on spirals on EBGs has been reported that addresses either the broadband EBG design challenges in the UHF frequency band or the integration of such structures with composite aircraft platforms. Therefore, the investigation, design, and development of an equiangular spiral antenna on an EBG are conducted for 425-800 MHz satellite communication applications. Starting from a mushroom EBG structure, analysis and simulations are undertaken to determine the dependency of antenna gain bandwidth, impedance bandwidth, pattern bandwidth, and axial ratio on the EBG geometry, materials, and height. A structural integration scheme is proposed, and a corresponding antenna plus EBG with nearly an octave bandwidth is designed, built, and tested that demonstrate good circularly polarized performance (gain greater than 4 dBi RHCP and axial ratio less than 3 dB). While further optimization of gain versus axial ratio versus EBG geometry and height is quite possible, the findings demonstrate the clear feasibility of a RHCP spiral antenna on a planar, tapered EBG with half the thickness of a traditional spiral on a reflector for composite structural integration

Analysis and synthesis of antenna arrays with respect to mutual coupling and beamforming

ato práce se zabývá analýzou a syntézou (zejména liniových) anténních řad umístěných ve volném prostoru nebo nad nekonečnou zemní rovinou. K charakterizaci problému byla odvozena teorie a algoritmus implementován v programu MATLAB. Pro liniové anténní řady se vyvinutá metoda se vyznačuje velkou rychlostí z důvodu použití vhodné aproximace proudového obložení na jednotlivých prvcích řady. Pro analýzu řad jsou využity modální techniky, tj. řada je charakterizována maticemi o rozměru NxN (kde N je počet prvků v řadě) popisujícími její impedační a vyzařovací vlastnosti. Tyto matice jsou následně podrobeny modálním rozkladům, jejichž výsledek poskytuje optimální buzení elementů pro dosažení daných vlastností – rezonance řady, činitel jakosti, směrovost. Kromě semi-analytických metod aplikovaných na liniové řady byl rovněž vyvinut algoritmus využívající simulátor elektromagnetického pole CST MWS, jež je pomocí maker propojen s programem MATLAB. Takto je možné syntetizovat vyzařovací diagram řady s libovolným typem elementů, tj. nikoli jen s dipóly. Výše zmíněné metody jsou aplikovány a ověřeny na několika příkladech: Optimalizace Yagi-Uda antény s různou délkou elementů, Optimalizace šířky pásma a směrovosti řady nad zemní rovinou, Řízení směrovosti kruhové řady, Syntéza supersměrového buzení řady, Syntéza daného vyzařovacího diagramu řady včetně zahrnutí vzájemných vazeb. V neposlední řadě jsou tyto příklady a techniky inspirací pro návrh a výrobu anténní řady na frekvenci 26 GHz. Tato řada byla vyrobena, změřena a bude implementována spolu s optickým systémem, který bude tvořit napájecí a přenosovou část pro systém 5G.This work deals with the analysis and synthesis of (especially linear) antenna arrays located in free space or above the infinite ground plane. The theory and algorithm implemented in MATLAB were derived to characterize the problem. For linear antenna array the developed method is characterized by a high computational speed due to the use of suitable current distribution approximation on individual elements of the array. Modal techniques are used to analyze the array, i.e., the array is characterized by matrices of N x N dimension (where N is the number of elements) describing its impedance and radiation properties. These matrices are then subject to modal decomposition, the result which provides optimal excitation of the elements to achieve given properties - resonance, quality factor, directivity. In addition to semi-analytical methods applied to linear arrays, an algorithm using electromagnetic field simulator CST MWS, which is connected to MATLAB by macros, was also developed. In this way, it is possible to synthesize a radiation pattern of an array with any type of element, i.e., not just dipoles. The above methods are tested and validated on several examples: Optimization of Yagi-Uda antenna with different element lengths, Optimization of bandwidth and directivity of an array above ground plane, Directivity control of circular array, Synthesis of super-directivity excitation of an array, Synthesis of a given radiation pattern of an array, including the mutual coupling. Last but not least, these examples and techniques are an inspiration for the design and manufacture of the 26 GHz antenna array. This array has been manufactured, measured and will be implemented together with an optical system that will form the power and transmission part to the 5G system

無指向性直列給電Sub-6帯基地局アンテナに関する研究

Tohoku University博士（工学）thesi