Study of mm-wave Fixed Beam and Frequency Beam-Scanning Antenna Arrays

Millimeter-wave frequencies are anticipated to be widely adapted for future wireless communication systems to resolve the demand of high data-rate and capacity issues. The millimeter-wave frequency range offers wide spectrum and a shift for most newly developing technologies as the microwave and lower frequency bands are becoming overcrowded and congested. These high frequency bands offer short wavelengths which has enabled the researchers to design and implement compact and adaptable antenna solutions. This research focuses on the implementation, transformation and modification of antenna structures used in lower frequency bands to millimeter-wave applications with high gain and multi-band and wideband performances. The first part of the thesis presents a microstrip patch array antenna with high gain in the upper 26 GHz range for 5G applications. The tolerance of the antenna, on widely used Rogers RT/duroid 5880 substrate, is observed with the edge-fed structure when curved in both concave and convex directions. In the second part of the thesis, 20 rectangular loops are arranged in a quasi-rhombic shaped planar microstrip grid array antenna configuration with dual-band millimeter-wave performance. A comparison with equal sized microstrip patch array is also presented to analyse the performance. The antenna operates in the upper 26 GHz band and has two frequency bands in close proximity. The third part of the thesis discusses the transition from wire Bruce array antenna to planar technology. Having been around for nearly a century and despite the simplicity of structure, the research community has not extended the concept of Bruce array antenna for further research. The proposed planar Bruce array antenna operates in three frequency v bands with optimization focus on 28.0 GHz band that has a directive fan-beam radiation pattern at broadside whereas the other two frequency ranges, above 30 GHz, have dual-beam radiation patterns which provide radiation diversity in narrow passages. The final part of the thesis deals with the transformation and modification of wire Bruce array antenna geometry to edge-fed printed leaky-wave antennas for millimeter-wave frequency scanning applications. In the first approach, the lengths of the unit-cell are optimised, without any additional circuitry, to enable two scanning ranges and mitigate the Open-Stopband, at broadside, for seamless scanning in the first range. A Klopfen-stein tapered divider is then deployed to make a linear array of the proposed antenna to achieve high gain. In the second approach, the horizontal and vertical lengths of the meandered unit-cell are replaced with semi-circular and novel bowtie elements, respectively, to obtain wide scanning range. The numerical results and optimizations have been performed using CST Micro-wave Studio where the effects of metallization and dielectric losses are properly consid-ered. The prototypes of the proposed antennas have been fabricated and experimentally validated

LEGO : linear embedding via Green's operators

Reduction of lead time has long been an important target in product development. Owing to the advance of computer power product optimization has been moved from the production stage to the preceding design stage. In particular, the full electromagnetic behavior of the final product can now be predicted through numerical methods. However, for the tuning of device parameters in the optimization stage, commercial software packages often rely on brute-force parameter sweeps. Further, for each set of parameter values a full recomputation of the entire configuration is usually required. In case of stringent product specifications or large complex structures, the computational burden may become severe. Recently, "marching on in anything" has been introduced to accelerate parameter sweeps. Nevertheless, it remains necessary to further reduce the computational costs of electromagnetic device design. This is the main goal in this thesis. As an alternative to existing electromagnetic modeling methods, we propose a modular modeling technique called linear embedding via Green’s operators (LEGO). It is a so-called diakoptic method based on the Huygens principle, involving equivalent boundary current sources by which simply connected scattering domains of arbitrary shape may fully be characterized. Mathematically this may be achieved using either Love’s or Schelkunoff’s equivalence principles, LEP or SEP, respectively. LEGO may be considered as the electromagnetic generalization of decomposing an electric circuit into a system of multi-port subsystems. We have captured the pertaining equivalent current distributions in terms of a lucid Green’s operator formalism. For instance, our scattering operator expresses the equivalent sources that would produce the scattered field exterior to a scattering domain in terms of the equivalent sources that would produce the incident field inside that domain. The enclosed scattering objects may be of arbitrary shape and composition. The scattering domains together with their scattering operators constitute the LEGO building blocks. We have employed various alternative electromagnetic solution methods to construct the scattering operators. In its most elementary form, LEGO is a generalization of an embedding procedure introduced in inverse scattering to describe multiple scattering be tween adjacent blocks, by considering one of the blocks as the environment of the other and vice versa. To establish an interaction between current distributions on disjoint domain boundaries we define a source transfer operator. Through such transfer operators we obtain a closed loop that connects the scattering operators of both domains, which describes the total field including the multiple scattering. Subsequently, a combined scattering block is composed by merging the separate scattering operators via transfer operators, and removing common boundaries. We have validated the LEGO approach for both 2D and 3D configurations. In the field of electromagnetic bandgap (EBG) structures we have demonstrated that a cascade of embedding steps can be employed to form electromagnetically large complex composite blocks. LEGO is a modular method, in that previously combined blocks may be stored in a database for possible reuse in subsequent LEGO building step. Besides scattering operators that account for the exterior scattered field, we also use interior field operators by which the field may be reproduced within (sub)domains that have been combined at an earlier stage. Only the subdomains of interest are stored and updated to account for the presence of additional domains added in subsequent steps. We have also shown how the scattering operator can be utilized to compute the band diagram of EBG structures. Two alternative methods have been proposed to solve the pertaining eigenvalue problem. We have validated the results via a comparison with results from a plane-wave method for 2D EBG structures. In addition, we have demonstrated that our method also applies to unit cells containing scattering objects that are perfectly conducting or extend across the boundary of the unit cell. The optimization stage of a design process often involves tuning local medium properties. In LEGO we accommodated for this through a transfer of the equivalent sources on the boundary of a large scattering operator to the boundary of a relatively small designated domain in which local structure variations are to be tested. As a result, subsequent LEGO steps can be carried out with great efficiency. As demonstrators, we have locally tuned the transmission properties at the Y-junction of both a power splitter and a mode splitter in EBG waveguide technology. In these design examples the computational advantageous of the LEGO approach become clearly manifest, as computation times reduce from hours to minutes. This efficient optimization stage of the LEGO method may also be integrated with existing software packages as an additional design tool. In addition to the acceleration of the computations, the reusability of the composite building constitute an important advantage. The Green’s operators are expressed in terms of equivalent boundary currents. These operators have been obtained using integral equations. In the numerical implementation of the LEGO method we have discretized the operators via the method of moments with a flat-facetted mesh using local test and expansion functions for the fields and currents, respectively. In the 2D case we have investigated the influence of using piecewise constant and piecewise linear functions. For the 3D implementation, we have applied the Rao-Wilton-Glisson (RWG) functions in combination with rotated RWG functions. After discretization, operators and operator compositions are matrices and matrix multiplications, respectively. Since the matrix multiplications in a LEGO step dominate the computational costs, we aim at a maximum accuracy of the field for a minimum mesh density. For LEGO with SEP, we have determined the unknown currents through inverse field propagators, whereas with LEP, the currents are directly obtained from the tangential field components via inverse Gram matrices. After a careful assessment of the computational costs of the LEGO method, it turns out that owing to the removal of common boundaries and the reusability of scattering domains, the most efficient application of LEGO involves a closely-packed configuration of identical blocks. In terms of the number of array elements, N, the complexity of a sequence of LEGO steps for 2D and 3D applications increases as O(N1.5) and O(N2), respectively. We have discussed possible improvements that can be expected from "marching on in anything" or multi-level fast-multipole algorithms. From an evaluation of the resulting scattered field, it turns out that LEGO with SEP is more accurate than with LEP. However, the spurious interior resonance effect common to SEP in the construction of composite building blocks can not simply be avoided through a combined field integral equation. By contrast, LEGO based on LEP is robust. Further, we have demonstrated that additional errors due to the choice of domain shape or building sequence, or the accumulation of errors due to long LEGO sequences are negligible. Further, we have investigated integral equations for the scattering from 2D and 3D perfectly conducting and dielectric objects. The discretized integral operators directly apply to the LEGO method. For scattering objects that are not canonical, these integral equations are used in the construction of the elementary LEGO blocks. Since we aim at a maximum accuracy of the field for a minimum mesh density, the regular test and expansion integral parts are primarily determined through adaptive quadrature rules, while analytic expressions are used for the singular integral parts. It turns out that the convergence of the scattered field is a direct measure for the accuracy of the scattered field computed with LEGO based on SEP or LEP. As an alternative to the PMCHW and the M¨uller integral equations, we have proposed an new integral equation formulation, which leads to cubic convergence in the 2D case, irrespective of the mesh density and object shape. In case of scattering object with a regular boundary domain scaling may be used to improve the convergence rate of the scattered field

Development of Q-band EPR/ENDOR spectrometer and EPR/ENDOR studies of dinitrosyl iron model complexes

A robust yet sensitive Q-band (35 GHz) cavity has been designed for routine variable temperature EPR (electron paramagnetic resonance) and ENDOR (electron nuclear double resonance) measurements down to 2 K. It consists of an aluminum or brass (plain, silver or gold plated) ribbon imbedded in a cylindrical epoxy or epoxy/quartz composite with a tunable piston at the bottom. The cavity has all the advantages of the traditional silver wire-wound cavity often used for Q-band measurements but is much more robust and easier to construct. The cavity suppresses degenerate resonant modes and minimizes wall eddy currents induced by field modulation. With standard Varian Q-band modulation coils, a 100-kHz modulation field of 27 G peak-to-peak is obtained at the sample. The cavity Q\rm\sb{L} ($\approx$2500) and weak pitch signal/noise ($\approx$1000:1) with a Varian/E-110 microwave bridge are comparable to those obtained with either a traditional wire-wound cavity or a cavity constructed with a thin silver wall on an epoxy/quartz substrate. A set of parallel posts along the axis of the cavity (bidirection) form the ENDOR coil. Dinitrosyl iron model complexes with ligands of cysteine, mercaptoethanol, thioglycolic acid, ethanethiol, penicillamine and imidazole were studied by EPR and ENDOR spectroscopy. X-band and Q-band ENDOR measurements have been made at various fields across the EPR envelope at temperatures from 2 K to 100 K. We have assigned most of the \sp1H resonances with reasonable certainty. The data confirm the thiol groups binding in the complexes with mercaptan ligands at room temperatures, and suggest that a structural rearrangement occurs with dinitrosyl iron cysteine and penicillamine upon freezing the sample, in which case coordination of both the thiol and amino group takes place. The assignment of axial EPR spectra to thiol coordination in every instance has also been cast in doubt by our data

Shaping of light beams with photonic crystals : spatial filtering, beam collimation and focusing

The research developed in the framework of this PhD thesis is a theoretical, numerical and experimental study of light beam shaping (spatial filtering, beam collimation and focusing) in the visible frequency range using photonic crystal structures. Photonic crystals (PhCs) are materials with periodic, spatially modulated refractive index on the wavelength scale. They are primarily known for their chromatic dispersion properties. However, they can also modify the spatial dispersion, which allows managing the spatial properties of the monochromatic light beams. In the first part of my thesis we experimentally show that particular spatial dispersion modification in PhCs can lead to spatial (angular) filtering of light beams. The study is focused on the spatial filtering efficiency improvement by introducing chirp (the variation of longitudinal period of the structure) in the crystal structure. Additionally, to enhance the effect, we consider different geometries and materials. The work presented in this PhD thesis brings closer to reality the creation of a new generation spatial filters for micro-photonic circuits and micro-devices. The second part of the study is devoted to the theoretical, numerical and experimental analysis of the formation of negative spatial dispersion in PhCs, which gives rise to collimation and focusing effects behind the PhCs. The ideas developed in my PhD also work in lossy systems, in particular in metallic PhCs. The simulation results for metallic PhCs are presented, in which both effects- spatial filtering and beam focusing, are shown.La recerca desenvolupada en el marc d'aquesta tesi doctoral és un estudi teòric, numèric i experimental de la modificació de la forma de feixos de llum (filtratge espacial, col·limació i focalització) en el rang visible de freqüències utilitzant estructures de cristall fotònic. Els cristalls fotònics (CFs) són materials amb una modulació periòdica de l'índex de refracció en l'escala de la longitud d'ona, i són principalment coneguts per les seves propietats relacionades amb la dispersió temporal. Tot i això, la dispersió espacial també pot ser modificada mitjançant CFs, fet que permet controlar les propietats espacials de feixos monocromàtics de llum. En la primera part de la tesi, mostrem experimentalment el fet que certes modificacions de la dispersió espacial en CFs poden donar lloc a filtratge espacial (angular) de feixos de llum. L'estudi es focalitza en la millora de l'eficiència del filtratge espacial mitjançant la introducció de "chirp" (la variació del període longitudinal de l'estructura) en el CF. A més, per tal d'incrementar l'efecte considerem diferents estructures i materials. El treball presentat en aquesta tesi doctoral acosta a la realitat la creació d'una nova generació de filtres espacials per a circuits micro-fotònics i micro-dispositius. La segona part d'aquest estudi se centra en l'anàlisi teòric, numèric i experimental de la formació de dispersió espacial negativa en CFs, la gual dóna lloc a efectes de col·limació i focalització un cop travessat el CF. Les idees desenvolupades en aquesta tesi doctoral també són aplicables a sistemes amb pèrdues, en particular a CFs metàl·lics. Els resultats de les simulacions mostren l'existència d'ambdós efectes, filtratge espacial i focalització, en CFs metàl·lics

Propagation of long waves of finite amplitude

We consider the radiation problem for long waves of- small amplitude, caused by an instantaneous disturbance of unit height at the origin. The equations governing this phenomrnon were derived by Long (1964). The asymptotic expressions for the wave front and for large times are obtained. The initial value problem for the non-linear system of equations is also solved, using a perturbation scheme based on the small parameter α, the non-dimensional amplitude of the disturbance. The sofution holds only for t < < I / α as a result of the appearance of a secular term in the fist order solution

Optimal Design of Photonic Crystals

Ph.DDOCTOR OF PHILOSOPH

Chiral Quantum Optics using Topological Photonics

Topological photonics has opened new avenues to designing photonic devices along with opening a plethora of applications. Recently, even though there have been many interesting studies in topological photonics in the classical domain, the quantum regime has remained largely unexplored. In this thesis, I will demonstrate a recently developed topological photonic crystal structure for interfacing a single quantum dot spin with a photon to realize light-matter interaction with topolog-ical photonic states. Developed on a thin slab of Gallium Arsenide(GaAs) mem- brane with electron beam lithography, such a device supports two robust counter- propagating edge states at the boundary of two distinct topological photonic crystals at near-IR wavelength. I will show the chiral coupling of circularly polarized lights emitted from a single Indium Arsenide(InAs) quantum dot under a strong magnetic field into these topological edge modes. Owing to the topological nature of these guided modes, I will demonstrate this photon routing to be robust against sharp corners along the waveguide. Additionally, taking it further into the cavity-QED regime, we will build a topological photonic crystal resonator. This new type of resonator will be based on valley-Hall topological physics and sustain two counter- propagating resonator modes. Thanks to the robustness of the topological edge modes to sharp bends, the newly formed resonators can take various shapes, the simplest one being a triangular optical resonator. We will study the chiral coupling of such resonator modes with a single quantum dot emission. Moreover, we will show an intensity enhancement of a single dot emission when it resonantly couples with a cavity mode. This new topological photonic crystal platform paves paths for fault-tolerant complex photonic circuits, secure quantum computation, and explor- ing unconventional quantum states of light and chiral spin networks