New quasi-TEM waveguides using artificial surfaces and their application to antennas and circuits

Research interest: In recent years we have seen the emergence of commercial applications at high frequencies, such as the top part of the microwave band and the millimeter and sub-millimeter bands, and it is expected a big increase in the coming years. This growing demand requires a rapid development of low-cost technology with good performance at these frequencies, where common technologies, such as microstrip and standard waveguides, have some shortcomings. In particular, existing solutions for high-gain planar scanning antennas at these frequencies su er from the disadvantages of these technologies giving rise to high-cost products not suitable for high volume production. Objectives: The main objective of this thesis is to study the feasibility of a new proposal to improve existing solutions to date for low-cost high-gain planar scanning antennas at high frequencies. This overall objective has resulted in another central objective of this thesis, which is the research of new quasi-TEM waveguides that are more appropriate than current technologies for the realization of circuits and components at these frequency bands. These guided solutions make use of periodic or arti cial surfaces in order to con- ne and channel the elds within these waveguides. Methodology: The work follows a logical sequence of speci c tasks aimed at achieving the main objective of this thesis. Chapter 2 presents the proposed guiding solution and shows its performance numerical and experimentally. The optimized design of high-gain antennas based on waveguide slot arrays requires the development of e cient ad-hoc codes. The implementation and validation of this code is presented in Chapter 3, where a new method for the analysis of corrugated surfaces is proposed, and in Chapter 4, which extends this code to the analysis of waveguide slot arrays. The process design and optimization of a two-dimensional array is described in Chapter 5, where a preliminary experimental validation is also described. Moreover, the proposed guiding solution has inspired the development of a new guiding technology of wider bandwidth and more versatile for the realization of circuits and components at high frequencies. Chapter 6 presents the contributions to the study of this technology and its application to the design of circuits.Alfonso Alós, E. (2011). New quasi-TEM waveguides using artificial surfaces and their application to antennas and circuits [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/11073Palanci

Impedance Transformers

Non

Hybrid optical integrator based on silicon-on-insulator platform

A hybrid optical integrator is a recirculating loop that performs oversampling typically for analog input, using the cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA). The modulated input signal changes the gain of the loop through XGM and thus modifies the loop accumulation. This thesis presents hybrid optical integrator for an all-optical analog-to-digital converter based on a silicon photonics platform. The device consists of silicon waveguides of dimension 220 × 500 nm (thick × width) and approximately 5 m optical loop length including fiber length, input and output grating couplers for 1550 nm signal, directional couplers, and external components (SOA, optical isolator and band-pass filter). The silicon photonics devices are designed for fabrication on the SOI wafer using E-Beam lithography. Fiber-optic integrator and hybrid optical integrator are constructed to demonstrate and evaluate a theoretical model for the system. The system is characterized for square waves at Mega-Hertz input frequencies. Experimental results show a sampling period of 28 ns and free spectral range of 35.7 MHz with an optical loop length of five meters, which is in excellent agreement with the theoretical model of the leaky integrator

Antennas and Arrays for Mobile Platforms -- Direct Broadcast Satellite and Wireless Communication

Flexibility of any proposed communication links is becoming one of the most challenging features. Direct broadcasting satellite services, for example, will be greatly enhanced by providing service-on-the-move. This market is very demanding as it necessitates the development of a low cost, low profile antenna that can be mounted on top of SUVs and minivans, which is capable of continuously tracking the satellite. Another example is the wireless antennas for laptops and smart-phones, where the antennas should fit within an extremely small volume and should be capable of addressing many services over wide frequency range. In this dissertation, both DBS and the wireless antennas are addressed. In these studies, efforts have been concentrated in developing low profile planar antennas, in particular, slot arrays. Travelling wave slotted waveguide arrays have been utilized to minimize the scanning angle range limits due to their inherent beam tilt angle. CNC machines were utilized first to fabricate the early prototypes for sub-array developments. Subsequently, a low cost fabrication technology is adopted to develop a low cost and light weight full array using substrate integrated waveguides (SIWs). The SIW is fully characterized and an excellent equivalent model has been derived to allow easy translation of metallic waveguide components to SIW. Various SIW junctions, transitions, and arrays have been developed for array feed networks including a 64 radiating SIW full array and a 32 radiating SIW array with folded feed. Meanwhile, for the wireless antennas, the utilization of reconfigurable hardware has been introduced to provide the required multi-functionality services and wide frequency coverage. Various reconfigurable antennas were developed and utilized to demonstrate their advantages compared to other design options such as wide-band or multi-band approaches. Both micro-electro-mechanical switches MEMS and PIN diodes have been successfully utilized to switch between the different configurations. The placement, control, and modeling of the switches are also discussed and novel modeling and biasing topologies are introduced. A novel and practical concept of reconfigurable multiband antenna is introduced here too, where advantages of both the multi-band and the reconfigurable antenna structures can be simultaneously achieved while supporting more services

Near-infrared Hong-Ou-Mandel interference on a silicon quantum photonic circuit

Near-infrared Hong-Ou-Mandel quantum interference is observed in silicon nanophotonic directional couplers with raw visibilities on-chip at 90.5%. Spectrally-bright 1557-nm two-photon states are generated in a periodically-poled KTiOPO4 waveguide chip, serving as the entangled photon source and pumped with a self-injection locked laser, for the photon statistical measurements. Efficient four-port coupling in the communications C-band and in the high-index-contrast silicon photonics platform is demonstrated, with matching theoretical predictions of the quantum interference visibility. Constituents for the residual quantum visibility imperfection are examined, supported with theoretical analysis of the sequentially-triggered multipair biphoton contribution and techniques for visibility compensation, towards scalable high-bitrate quantum information processing and communications.Comment: 15 pages, 6 figure

Ku-band multiple beam antenna

The frequency reuse capability is demonstrated for a Ku-band multiple beam antenna which provides contiguous low sidelobe spot beams for point-to-point communications between any two points within the continental United States (CONUS), or regional coverage beams for direct broadcast systems. A spot beam antenna in the 14/21 GHz band which provides contiguous overlapping beams covering CONUS and two discrete beams covering Hawaii and Alaska were designed, developed, and tested. Two reflector antennas are required for providing contiguous coverage of CONUS. Each is comprised of one offset parabolic reflector, one flat polarization diplexer, and two separate planar array feeds. This antenna system provides contiguous spot beam coverage of CONUS, utilizing 15 beams. Also designed, developed and demonstrated was a shaped contoured beam antenna system which provides contiguous four time zone coverage of CONUS from a single offset parabolic reflector incorporating one flat polarization diplexer and two separate planar array feeds. The beams which illuminate the eastern time zone and the mountain time zone are horizontally polarized, while the beams which illuminate the central time zone and the pacific time zone are vertically polarized. Frequency reuse is achieved by amplitude and polarization isolation

Analysis of guided and leaky modes of circular waveguides and realization of mechanical tunable metamaterial and devices

The guided and leaky mode characteristics for planar dielectric structures are relatively well known, due to its various kind of applications. However, the investigation to the modes characteristics for a circular rod structure is relatively rare, especially for the leaky modes, despite the rod structure is very simple and useful. Accordingly, in the first part of the thesis, we analyze the guided and leaky modes for a circular dielectric rod in detail. The analysis is carried out in several steps. First, by considering the field distributions outside the rod, the modes are well defined and classified based on their physical meanings. The relations for the mode solutions using different types of special functions and Riemann sheets are figured out. Further, completed forms of characteristic equations used to solve different modes are presented explicitly. Second, in order to solve this nonlinear characteristic equation efficiently and accurately, we employ iterative methods and spent lots of efforts in deriving the initial guess expression in a simply but efficient form. Through using the asymptotic expansion method and employing the Lambert W function, we derive the initial guesses around the cutoff frequency, low frequency limit and high frequency limit for both TM and TE cases. Finally, the numerical results are presented for the complex transverse propagation constants of proper and two types of improper modes for both cases. Some of the improper modes have not been shown in literatures. Next, we extend the analysis to the circular rod with negative permittivity and permeability (double negative material (DNG)). Following the same analysis procedure for the conventional dielectric circular rod, first, we derive the characteristic equation for the DNG case and de fine different types of modes. Second, we expand the characteristic equation asymptotically and then find the initial guess expression for different types of modes around the cutoff, high frequency limit and low frequency limit. Finally, using these initial guesses we solve the char acteristic equation with iterative methods and find the dispersion curves. xi The electromagnetic (EM) material property of simultaneous negative permittivity and per meability we use for the DNG rod analysis actually can not be found in nature so far. The method in generating material with DNG property is using metamaterials. In the second part of the thesis we introduce metamaterials, and discuss our work of realizing tunable metamate rials in detail. This type of tunable property allows the metamaterial device to overcome the drawback of fixed and limited bandwidth from the conventional metamaterials. We start it from presenting a novel tunable and flexible SRR-based meta-atom capable of tuning its EM response characteristics over a broad frequency range by simple mechanical stretching. First, we design and simulate a meta-atom with a liquid metal as the resonator material. The liquid metal is patterned to be a SRR structure and embedded inside a highly stretchable silicone elastomer. Due to its liquid nature, the liquid metal-based SRR could flow in response to an applied strain, and compliant to change from the encasing elastomer as the meta-atom being stretched and twisted. Therefore, through simple mechanical stretching, the shape of the SRR is changed. Correspondingly, the equivalent capacitance and inductance of the SRR are adjusted, thus tuning the resonance frequency of the meta-atom. The shifting trend of the resonance frequency with different stretching orientations is predicted by a simple circuit mode, and verified from the experiment. Next, we extend the idea of meta-atom to the meta-skin, which is composed of an array of meta-atoms. This meta-skin performed as a tunable selective surface with a wide resonance frequency tuning range when being stretched. Further, due to its flexibility, this meta-skin can function as a flexible “cloaking” surface in suppressing the scattering from the dielectric ob ject. As examples, we demonstrate frequency selective responses of multilayer meta-skins with different stretching ratio in the planar direction. Also, we investigate scattering suppression effect of the meta-skin coated on a finite-length dielectric rod in free space. Benefit from the liquid metal and highly stretchable elastomer, we design and realize a directivity reconfigurable two-arm spiral antenna. This new device has the ability to reconfig urate the radiation pattern along the main lobe direction by control the shape of the antenna, as the radiation pattern becomes sharper, directivity is optimized. Finally, the directivity, efficiency, and axial ratio with different dome height, operating frequencies are presented

Magnetoinductive waves in metamaterial-based structures

Metamaterials are artificial structures that exhibit unusual properties not seen in natural materials achieved by designing the composite unit cells on the subwavelength scale. Magnetic metamaterials consist of magnetically coupled resonators. Strong magnetic interactions between the unit cells in magnetic metamaterials give rise to magnetoinductive (MI) waves, which are slow waves with wavelengths shorter than the free-space electromagnetic wavelengths. The aim of this thesis is to present our studies on three novel applications of metamaterialbased structures for manipulating MI waves. The flexible designs of metamaterial-based structures allow one to tailor the dispersion characteristics of MI waves. Analytical models are established based on the MI wave properties, which are verified by numerical and experimental results. We first propose an approach for signal-guiding to specified directions and realising nearfield directionality via multiple channels in a MI waveguide, which is potentially useful for wireless power or data transfer. Employing two sources with a phase difference to a MI waveguide can suppress the waves travelling to one end. Analytical calculations and experimental validations are presented for both axial and planar structures operating in the microwave regime. Selective unidirectional signal propagation is also demonstrated for nanostructured metamaterial arrays, where there is purely electric coupling and electroinductive (EI) waves are supported, with analytical predictions verified by numerical calculations. Separating the sources by two unit cells leads to a split in the passband, and MI waves travel in opposite directions within the two branches. Such a system can be treated as a special case of diatomic structures with dual dispersion branches featuring both forward and backward waves. We thus propose and prove a fundamental rule that the direction of guided signals is controllable by the forward or backward nature of the supported MI or EI waves in a structure. The sensitivity of resonant meta-atoms to the variations in local electromagnetic fields makes MI waveguides attractive for near-field remote sensing applications. We devise a 1D position sensor that supports MI waves. With single-port probing, a low-complexity algorithm (we named it as the Odd-Even algorithm) is developed for localising a metal object in close proximity. The localisation procedure relies on the unique reflection patterns of MI waves due to the standing waves formed between the signal injection point and the defect in the array created by the presence of the metal object. Weaker interactions between the object and the defect lead to increased difficulties for localisation. It is shown that terminating the array end with a matching load can suppress the interfering reflections, and improve localisation accuracy. The accuracy of the Odd-Even algorithm tested on the measured and analytically calculated reflection patterns are presented. In this proof-of-principle study, the possibility for remote discrete localisation of a conducting object on the MI sensing waveguide using a low-complexity algorithm has been demonstrated. We then proceed to analyse far-field properties of structures supporting MI waves. Superdirectivity refers to antenna structures with directivity higher than that of a phased array of the same size, and it can be realised by a dimer of two magnetically coupled split ring resonators (SRRs), by exciting only one of the elements and imposing MI waves. The slow-wave nature of MI waves enables rapid spatial variation in the current distribution among elements, which is essential for achieving superdirectivity. In order to enable quick characterisation of superdirective structures that can be approximated as dipoles, we introduce new 2D equivalents to the traditional 3D directivity. The theoretical maximum achievable directivity values as well as the optimum conditions, for both the 3D and planar directivities are derived. Analytical results are verified and supported by the observations based on numerical calculations. It is shown that by optimising the planar directivity in the azimuthal plane, the 3D directivity is optimised simultaneously. We also demonstrate superdirectivity experimentally by measuring the in-plane field distribution produced by a dimer antenna. It is the first time that superdirectivity is realised using a PCB dimer structure. Three areas of potential applications of MI waves are developed in this thesis, expanding the possibilities of near- and far-field manipulations using metamaterial-based structures by imposing MI waves