Dissertations / Theses on the topic 'Broadband matching'

"In the design of any antenna radiator, single or multi-element, a significant amount of time and resources is spent on impedance matching. There are broadly two approaches to impedance matching; the first is the distributed impedance matching approach which leads to modifying the antenna geometry itself by identifying appropriate degrees of freedom within the structure. The second option is the lumped element approach to impedance matching. In this approach instead of modifying the antenna geometry a passive network attempts to equalize the impedance mismatch between the source and the antenna load. This thesis introduces a new technique of impedance matching using lumped circuits (passive, lossless) for electrically small (short) non-resonant dipole/monopole antennas. A closed form upper-bound on the achievable transducer gain (and therefore the reflection coefficient) is derived starting with the Bode-Fano criterion. A 5 element equalizer is proposed which can equalize all dipole/monopole like antennas. Simulation and experimental results confirm our hypothesis. The second contribution of this thesis is in the design of broadband, small size, modular arrays (2, 4, 8 or 16 elements) using the distributed approach to impedance matching. The design of arrays comprising a small number of elements cannot follow the infinite array design paradigm. Instead, the central idea is to find a single optimized radiator (unit cell) which if used to build the 2x1, 4x1, 2x2 arrays, etc. (up to a 4x4 array) will provide at least the 2:1 bandwidth with a VSWR of 2:1 and stable directive gain (not greater than 3 dB variation) in each configuration. Simulation and experimental results for a solution to the 2x1, 4x1 and 2x2 array configurations is presented. "

The purpose of this project is to study the real frequency parametric approach and to implement it in MATLAB as a CAD matching network synthesizer. This approach uses the parametric presentation of Brune function for modeling the real part of the immittance function of the lossless equalizer, which improves the computational time and numerical stability. The parametric approach inherits all the merits of the former real frequency direct computational technique; therefore, it is able to provide optimized solutions for double matching problems as well as the single matching problems.

The parametric approach is applied to examples presented in this project including a double matching problem and a single matching problem. In addition, different topologies of the equalizer are presented in each matching problem. To compare the behavior and the efficiency of each matching network, wideband S-parameter simulation for each scenario is generated by Agilent Design System (ADS) software.

Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008.
First, Phillip, Committee Member ; Adibi, Ali, Committee Member ; Raman, Chandra, Committee Member ; Buck, John, Committee Member ; Trebino, Rick, Committee Chair.

This thesis describes the outcome of study to investigate methods of broadband matching to photonic devices such as lasers and high speed detectors. The thesis is divided into two areas of interest relating to the design of broadband fiber optic links. The first area is the application of numerical methods and commensurate line methods to the design of compact equalisers which allow an improved transducer power gain over a wide band. It is shown that physically small equalisers can yield an improvement of 4 dB over a 2 GHz bandwidth. The second area considered is the distortion inherent in a laser diode. Detailed measurements of the second order and intermodulation products are given. A small signal perturbation analysis is presented which helps to explain the observed distortion products. The results of numerical simulation of the distortion using a state variable implementation of the full rate equations and related first, second and intermodulation equations is presented and possible methods of reducing the distortion are explored. It is shown that in principle the distortion could be reduced by pre-generating the distortion and adding an inverted form of the distortion to the transmitted signal. The distortion can then be corrected in the fiber and simulation studies suggest that an improvement of 13 dB optical or 26 dB electrical may be possible.

This Thesis is an embodiment of some research work carried out towards achieving faster and more reliable handover techniques in a Mobile WiMAX (Worldwide Interoperability for Microwave Access) network. Handover, also called handoff, is the critical mechanism that allows an ongoing session in a cellular mobile network like WiMAX to be seamlessly maintained without any call drop as the Mobile Station (MS) moves out of the coverage area of one base station (BS) to that of another. Mobile WiMAX supports three different types of handover mechanisms, namely, the hard handover, the Fast Base Station Switching (FBSS) and the Micro-Diversity Handover (MDHO). Out of these, the hard handover is the default handover mechanism whereas the other two are the optional schemes. Also, FBSS and MDHO provide better performance in comparison to hard handover, when it comes to dealing with the high-speed multimedia applications. However, they require a complex architecture and are very expensive to implement. So, hard handover is the commonly used technique accepted by the mobile broadband wireless user community including Mobile WiMAX users. The existing Mobile WiMAX hard handover mechanism suffers from multiple shortcomings when it comes to providing fast and reliable handovers. These shortcomings include lengthy handover decision process, lengthy and unreliable procedure of selecting the next BS, i.e., the target BS (TBS) for handover, occurrence of frequent and unwanted handovers, long connection disruption times (CDT), wastage of channel resources, etc. Out of these, reducing the handover latency and improving the handover reliability are the two issues that our present work has focused on. While the process of selecting the TBS for handover adds to the overall delay in completing the process of handover, choosing a wrong TBS for handover increases the chance of further unwanted handovers to occur or even a call drop to occur. The latter greatly hampers the reliability of a handover. In order to contribute to the solution of the above two problems of slow handover and unreliable handover, this Thesis proposes and investigates three handover techniques, which have been called Handover Techniques 1, 2 and 3, respectively. Out of these three techniques, the first two are fully MS-controlled while the third one is a dominantly serving BS-controlled. In Handover Techniques 1 and 2, which share between them some amount of commonness of ideas, the MS not only itself determines the need for a handover but also self-tracks its own independent movement with respect to the location of the (static) neighboring BSs (NBS). N both these handover techniques, the MS performs distance estimation of the NBSs from the signal strength received from the NBSs. But they (the two handover techniques) employ different kinds of “lookahead” techniques to independently choose, as the TBS, that NBS to which the MS is most likely to come nearest in the future. Being MS-controlled, both Handover Technique 1 and Handover Technique 2 put minimal handover-related workload on their respective SBSs who thus remain free to offer services to many more MSs. This interesting capability of the two handover techniques can increase the scalability of the WiMAX network considerably. In Handover Technique 3, which is a BS-controlled one with some assistance received from the MS, the SBS employs three different criteria or parameters to select the TBS. The first criterion, a novel one, is the orientation matching between the MS’s direction of motion and the geolocation of each NBS. The other two criteria are the current load of each NBS (the load provides an indication of a BS’s current QoS capabilities) and the signal strength received by the MS from each NBS. The BS assigns scores to each NBS against each of the three independent parameters and selects the TBS, which obtains the highest weighted average score among the NBSs. All three handover techniques are validated using simulation methods. While Handover Techniques 1 and 2 are simulated using Qualnet network simulator, for Handover Technique 3, we had to design, with barest minimum capability, our own simulation environment, using Python. Results of simulation showed that for Handover Techniques 1 and 2, it is possible to achieve around 45% improvement (approx) in the overall handover time by using the two proposed handover techniques. The emphasis in the simulation of the Handover Technique 3 was on studying its reliability in producing correct handovers rather than how fast handovers are. Five different arbitrary pre-defined movement paths of the MS were studied. Results showed that with orientation matching or orientation matching together with signal strength, reliability was extremely good, provided the pre-defined paths were reasonably linear. But reliability fell considerably when relatively large loads were also considered along with orientation matching and signal strength. Finally, the comparison between the proposed handover techniques in this Thesis and few other similar techniques in Mobile WiMAX proposed by other researchers showed that our techniques are better in terms providing fast, reliable and intelligent handovers in Mobile WiMAX networks, with scalability being an added feature.

This research presents design techniques for a linear power amplifier with high efficiency in wireless handsets. The power amplifier operates with high efficiency at the saturated output power, maintains high linearity with enhanced efficiency at back-off power levels, and covers a broadband frequency response. The amplifier is thus able to operate in multiple modes (2G/2.5G/3G/4G). The design techniques provide contributions to current research in handset power amplifiers, especially to the converged power amplifier architecture, to reduce the number of power amplifiers within the handset while covering all standards and frequency bands around the globe. Three main areas of interest in power amplifier design are investigated: high power efficiency; high linearity; and broadband frequency response. Multiple techniques for improving the efficiency are investigated with the focus on maintaining linear operation. The research applies a new technique to the handset industry, class-J, to improve the power efficiency while avoiding the practical issues that hinder the typical techniques (class-AB and class-F). Class-J has been implemented using GaN FET in high power applications. To our knowledge, this work provides the first implementation of class-J using GaAs HBT in a handset power amplifier. The research investigates the linearity, and the nature and causes of nonlinearities. Multiple concepts for improving the linearity are presented, such as avoiding odd-degree harmonics, and linearizing the relationship between the output current and the input voltage of the amplifier at the fundamental frequency. The concept of bias depression in HBT transistors is introduced with a bias circuit that reduces the bias-offset effect to improve linearity at high output power. A design methodology is presented for broadband matching networks, including the component loss. The methodology offers a quick and accurate estimation of component values, giving more degrees of freedom to meet the design specifications. It enables a trade-off among high out-of-band attenuation, number/size of components, and power loss within the network. Although the main focus is handset power amplifiers, most of the developed techniques can be applied to a wide range of power amplifiers.
Ph. D.

Optical parametric frequency conversion based on quasi phase matching (QPM) in nonlinear optical crystals is a powerful technique for generating coherent radiation in wavelength ranges spanning from the mid-infrared (mid-IR) to the blue, displaying low thermal load and high efficiency.This thesis shows how QPM in one- (1D) or two-dimensional (2D) lattices can be employed to engineer novel devices for parametric downconversion in the IR, af-fording freedom in designing both spectral and angular properties of the parametric output. Experimental demonstrations of parametric devices are supported by theoreti-cal modelling of the nonlinear conversion processes.In particular, broadband parametric downconversion has been investigated in 1D QPM lattices, through degenerate downconversion close to the point of zero group-velocity dispersion. Ultra-broadband optical parametric generation (OPG) of 185 THz bandwidth (at 10 dB), spanning more than one octave from 1.1 to 3.7 μm, has been achieved in periodically poled 1 mol% MgO-doped near-stoichiometric LiTaO3 (MgSLT) of 25 μm QPM period, pumped at 860 nm. Such broadband gain is of high interest for ultrashort optical pulse amplification, with applications in high harmonic generation, ultrafast spectroscopy and laser ablation. Furthermore, the det-rimental impact of parasitic upconversion, creating dips in the OPG spectrum, has been investigated. By altering the pump pulse duration, energy can be backconverted to create peaks at the involved OPG wavelengths, offering a possible tool to enhance broadband parametric gain spectra.The engineering of the angular properties of a parametric output benefits greatly from 2D QPM, which is investigated in this thesis by the specific example of hexagonally poled MgSLT. It is demonstrated how two OPG processes, supported by a single 2D QPM device, can exhibit angularly and spectrally degenerate signals (idlers). This degeneracy results in a coherent coupling between the two OPG pro-cesses and a spectrally degenerate twin-beam output in the mid-IR (near IR). 2D QPM devices exhibiting such coherently coupled downconversion processes can find applications as compact sources of entangled photon-pairs. This thesis further illus-trates the design freedom of 2D QPM through the demonstration of a device support-ing multiple parametric processes, thus generating multiple beams from the mid-IR to the blue spectral regions.

QC 20131204

As the interest in intentional electromagnetic interference (IEMI) increases, so does the need of a suitable antenna which endures those demanding conditions. The ultrawideband (UWB) technology provides an elegant way of generating high-voltage UWB pulses which can be used for IEMI. One UWB antenna, invented solely for the purpose of radiating pulses, is the impulse radiating antenna (IRA). In the course of this master thesis work, a suitable geometry of the IRA is suggested, and modelled, for the high-voltage application of 90 kV.

Le problème de l'adaptation d'impédance en ingénierie des hyper fréquences et en électronique en général consiste à minimiser la réflexion de la puissance qui doit être transmise, par un générateur, à une charge donnée dans une bande de fréquence. Les exigences d'adaptation et de filtrage dans les systèmes de communication classiques sont généralement satisfaites en utilisant un circuit d'adaptation suivi d'un filtre. Nous proposons ici de concevoir des filtres d'adaptation qui intègrent à la fois les exigences d'adaptation et de filtrage dans un seul appareil et augmentent ainsi l'efficacité globale et la compacité du système. Dans ce travail, le problème d'adaptation est formulé en introduisant un problème d'optimisation convexe dans le cadre établi par la théorie de d'adaptation de Fano et Youla. De ce contexte, au moyen de techniques modernes de programmation semi-définies non linéaires, un problème convexe, et donc avec une optimalité garantie, est obtenu. Enfin, pour démontrer les avantages fournis par la théorie développée au-delà de la synthèse de filtres avec des charges complexes variables en fréquence, nous examinons deux applications pratiques récurrentes dans la conception de ce type de dispositifs. Ces applications correspondent, d'une part, à l'adaptation d'un réseau d'antennes dans le but de maximiser l'efficacité du rayonnement, et, d'autre part, à la synthèse de multiplexeurs où chacun des filtres de canal est adapté au reste du dispositif, notamment les filtres correspondant aux autres canaux
The problem of impedance matching in electronics and particularly in RF engineering consists on minimising the reflection of the power that is to be transmitted, by a generator, to a given load within a frequency band. The matching and filtering requirements in classical communication systems are usually satisfied by using a matching circuit followed by a filter. We propose here to design matching filters that integrate both, matching and filtering requirements, in a single device and thereby increase the overall efficiency and compactness of the system. In this work, the matching problem is formulated by introducing convex optimisation on the framework established by the matching theory of Fano and Youla. As a result, by means of modern non-linear semi-definite programming techniques, a convex problem, and therefore with guaranteed optimality, is achieved. Finally, to demonstrate the advantages provided by the developed theory beyond the synthesis of filters with frequency varying loads, we consider two practical applications which are recurrent in the design of communication devices. These applications are, on the one hand, the matching of an array of antennas with the objective of maximizing the radiation efficiency, and on the other hand the synthesis of multiplexers where each of the channel filters is matched to the rest of the device, including the filters corresponding to the other channels

La thèse étudie en profondeur l'un des problèmes classiques de la conception de circuits RF, le problème de l'adaptation d'impédance. L’adaptation d’impédance consiste à maximiser le transfert de puissance d'une source à une charge dans une bande de fréquences. Les antennes sont l'un des dispositifs classiques dans lesquels l'adaptation d'impédance joue un rôle important. La conception d'un circuit d'adaptation pour une charge donnée revient principalement à trouver une matrice de diffusion sans perte qui, lorsqu'elle est enchaînée à la charge, minimise la réflexion de la puissance dans l'ensemble du système.Dans ce travail, les aspects théoriques du problème de l'adaptation et l'applicabilité pratique des approches développées sont dûment pris en compte. La partie I de la thèse couvre deux approches différentes mais étroitement liées du problème de l'adaptation large bande. Le cadre développé dans la première approche consiste à trouver la meilleure approximation H infini d'une fonction L infini, Փ via la théorie de Nehari. Cela revient à réduire le problème à un problème généralisé de valeurs propres basé sur un opérateur défini sur H2, l'opérateur de Hankel, HՓ. La réalisabilité d'un gain donné est fournie par la contrainte, opérateur norme de HՓ inférieure ou égale à un. La seconde approche formule le problème de l'adaptation comme un problème d'optimisation convexe où une plus grande flexibilité est fournie aux profils de gain par rapport à l'approche précédente. Il est basé sur deux théories riches, à savoir la théorie de l'adaptation de Fano-Youla et l'interpolation analytique. La réalisabilité d'un gain donné est basée sur les conditions de dé-chaînage de Fano-Youla qui se réduisent à la positivité d'une matrice classique en théorie d'interpolation analytique, la matrice de Pick. La concavité de la matrice de Pick concernée permet de trouver la solution au problème au moyen de l'implémentation d'un problème de programmation semi-défini non linéaire. Ainsi, nous estimons des limites inférieures nettes au niveau d'adaptation pour les circuits d'adaptation de degré fini et fournissons des circuits atteignant ces limites.La partie II de la thèse vise à réaliser les circuits d'adaptation sous forme de réseaux en échelle constitués d'inductances et de condensateurs et aborde également certaines contraintes importantes de réalisabilité. Les circuits d'adaptation sont conçus pour plusieurs antennes non-adaptées, testant la robustesse de l'approche développée. La théorie développée dans la première partie de la thèse offre un moyen efficace de comparer le niveau d'adaptation atteint aux limites théoriques
The thesis makes an in-depth study of one of the classical problems in RF circuit design,the problem of impedance matching. Matching problem addresses the issue of transmitting the maximum available power from a source to a load within a frequency band. Antennas are one of the classical devices in which impedance matching plays an important role. The design of a matching circuit for a given load primarily amounts to find a lossless scattering matrix which when chained to the load minimize the reflection of power in the total system.In this work, both the theoretical aspects of the broadband matching problem and thepractical applicability of the developed approaches are given due importance. Part I of the thesis covers two different yet closely related approaches to the matching problem. These are based on the classical approaches developed by Helton and Fano-Youla to study the broadband matching problems. The framework established in the first approach entails in finding the best H infinity approximation to an L infinity function, Փ via Nehari's theory. This amounts to reduce the problem to a generalized eigen value problem based on an operator defined on H2, the Hankel operator, HՓ. The realizability of a given gain is provided by the constraint, operator norm of HՓ less than or equal to one. The second approach formulates the matching problem as a convex optimisation problem where in further flexibility is provided to the gain profiles compared to the previous approach. It is based on two rich theories, namely Fano-Youla matching theory and analytic interpolation. The realizabilty of a given gain is based on the Fano-Youla de-embedding conditions which reduces to the positivity of a classical matrix in analytic interpolation theory, the Pick matrix. The concavity of the concerned Pick matrix allows finding the solution to the problem by means of implementing a non-linear semi-definite programming problem. Most importantly, we estimate sharp lower bounds to the matching criterion for finite degree matching circuits and furnish circuits attaining those bounds.Part II of the thesis aims at realizing the matching circuits as ladder networks consisting of inductors and capacitors and discusses some important realizability constraints as well. Matching circuits are designed for several mismatched antennas, testing the robustness of the developed approach. The theory developed in the first part of the thesis provides an efficient way of comparing the matching criterion obtained to the theoretical limits

碩士
國立臺中技術學院
多媒體設計研究所
94
The main source of revenue of Internet and traditional media are advertisement. In order to grab consumers' attention, presentation of Internet advertising comes with more varieties and diversities with innovated technologies as time goes by. Due to the popularization of the Broadband network, Internet advertisement utilizes streaming technology to transmit sound or video-information through the network, and provides real-time listening or viewing of goods information to reinforce consumers’ impression on Brand Awareness. This type of advertising is named as Broadband Video Commercial by the American Interactive Advertising Bureau. The greatest difference between Broadband Video Commercial and traditional banner advertisement is that Broadband Video Commercial has streaming films with the characteristic of timeline. Broadband Video Commercial is often inserted among stream programs by broadband video websites. We observed inefficient ways how most broadband video websites owners receive advertisement businesses via telephone and E-mail, and manually arrange the broadcasting of advertisement. The main purpose of this study is to build an Internet advertisement matching system. Through the match system, advertisers are able to publish personalized advertisement to target customer group by matching advertisement conditions with users’ preferences. It is anticipated to automate the process of publish advertisement and match advertisement target consumer groups by using information technology, and further raise advertisers’ willingness to advertise, and increase broadband video sites’ sales revenue.

碩士
國立臺灣大學
光電工程學研究所
98
The research topics of this thesis focus on quasi-phase-matching (QPM) frequency conversion using periodically poled lithium tentalate (PPLT) and periodically poled MgO-doped lithium niobate (PPMgO:LN). This thesis is mainly organized into two parts: (a) Structure design of PPMgO:LN with broadbandly accepted temperature bandwidth for second harmonic generation (SHG) and its experiment to verify the SHG conversion efficiency and the temperature bandwidth. (b) Design of PPLT for singly resonant optical parametric oscillator (SROPO) and using green pump laser for blue and white light generation. For the QPM SHG experiment with single pass configuration, 5mm long PPMgO:LN with ten QPM periodicities was pumped by a Nd:YVO4 Q-switched 1064nm laser. The accepted temperature bandwidth was found to be 49°C, and the conversion efficiency exceeded 20%. Compared with a 5mm PPMgO:CLN with single QPM periodicity, the accepted temperature bandwidth increases from 5.?°C to 49°C and the maximum conversion efficiency decreases from 6?% to 27%. For the up-conversion blue generation, with the design of multi-QPM periodicities for the cascaded OPO-SHG process, the slope efficiency for the 465nm blue generation, as pumped by a pulsed green laser, reacheed 16%. The linewidth of 465nm blue was broadened to be 0.78nm. By changing the duty cycle of the poling area in PPCLT, the slope efficiency of up-conversion 435nm blue generation increased to 21%. For the white generation experiment, we used a 25mm long PPCLT where OPO-SHG cascaeded process generates blue and OPO generates red. When the power of green pump reachesd 370mW, we observed simultaneous generation of 465nm blue laser with 25mW power and 630mW with 45mW. If proper power of residual 532nm green laser was selected, then white laser with 100mW power and chromaticity coordinate located in (0.3333, 0.3333) could be realized.

碩士
國立臺灣大學
光電工程學研究所
100
This thesis focuses on quasi-phase matching (QPM) frequency con-ver¬sion using periodically poled lithium tantalite (PPLT). It is composed of two parts： (1) Design and characterization of cascaded optical parametric oscillation (OPO) with second harmonic generation (SHG), and (2) the integration of optical structure of cascade OPO-SHG blue and OPO-red lasers to make blue light and white light laser. First of all, multi-periodicity SHG cascading OPO is used to generate blue light laser with a wavelength of 465nm. Then with the help of apodizing, the phase delay can be reduced and thus the conversion efficiency and the generated blue linewidth can be improved to 18% and about 1.83nm, respectively. Second, in order to improve green laser source with speckle reduction, multi-periodicity SHG with apodizing structure in green laser crystal is used. By using a broadband inferred pump made by an OPO process, the SHG green light conversion efficiency can reach about 10% and the linewidth of the green light can be expanded up to 5nm, which reduces the speckle contrast to less than 5%. Finally, based on QPM PPLT, a 200mW white light laser source is fabricated when pumped by a 1W pulsed green laser. At an average green pump of 1W, 56mW and 83.03mW power for blue and red light were obtained. The total power is of 200mW white light with chromaticity coordinates (0.3141,0.3194,0.3665) and color temperature of 6489 K. The high conversion efficiency 20% was ascribed to the extended spectral line¬width of the blue and red bandwidth, exceeding 1nm.

碩士
國立臺灣大學
光電工程學研究所
101
This thesis is composed of three parts：an introduction of the theory of quasi-phase-matching (QPM) and the principle of the optical parametric oscillator (OPO), the fabrication technique of one-dimensional periodically poled congruent grown lithium tantalite (LiTaO3) for cascade OPO-SHG 465nm blue laser and the measurement and analysis of OPO-SHG blue light generators. First of all, the mechanism of nonlinear frequency conversion and QPM theory, and its application to the optical parametric oscillator and second harmonic generation (SHG) are introduced. By using Sellmeier equation, the QPM period of periodically poled LiTaO3 (PPLT) for the above application is designed. By taking advantage of the nickel-diffusion with high-voltage poling process, cascaded OPO-SHG devices on 0.5mm-thick congruent LiTaO3 substrate is fabricated. For cascaded OPO-SHG PPLT device, a multi-period SHG segment composed of single period, three periods , apodized and fan-out structure design for QPM-SHG is proposed. The period for OPO is 7.7576um, and the period for SHG is 4.9865um with single period；4.9514 um, 4.9865 um, and 5.0218 um with three periods；gradually changing from 4.9164um to 5.0749 um with an apodized structure design and gradualy changing from 4.9024 um to 5.0606 um with a parallel fan-out structure design. With this design, a 20mm-long chipwafer for generating OPO-SHG broadband blue light can be achieved. Using a 1064nm infrared laser with 14ns pulse width as the pump source, a cascaded OPO-SHG chip in a concave laser cavity is shown to generate a 465nm broadband blue laser. Discussing the comparison of the optical measurement between single period, three periods, and apodized structure design for SHG, this work also includes the optical measurement of fan-out structure design . An average output power of 26.8 mW blue light laser has been achieved under a 752 mW input green power, which corresponds to a conversion efficiency of 3.56% . The spectrum is shown to have a 1.9 nm bandwidth and 8.3% slope efficiency.