Dissertations / Theses on the topic 'Directional Microwave'

Thesis (MScEng)--University of Stellenbosch, 2001.
ENGLISH ABSTRACT: The application of artificial neural networks to microwave circuits is investigated. A neural network model is developed for two parallel waveguides coupled by a longitudinal slot in the common broad wall. Training data is generated through a moment method solution of the integral equations that describe the structure. A systematic investigation of training options is carried out and the development of the model is described in detail. The model is evaluated and compared with an Adaptive Sampling Interpolation (ASI) Technique. The neural network is found to be less accurate than the ASI Technique at a much greater expense of development time and required user supervision.
AFRIKAANSE OPSOMMING: Die toepassing van neurale netwerke op mikrogolfbane is ondersoek. In Neurale netwerk-model is ontwikkel vir twee parallelle golfleiers met longitudinale gleufkoppeling in die gemeenskaplike bree wand. Data vir die opleiding van die netwerke is verkry deur In momentmetode-oplossing van die integraalvergelykings wat die struktuur beskryf. Verskillende ontwerpsopsies vir die netwerke is stelselmatig ondersoek en die ontwikkelingsproses van die netwerk is volledig beskryf. Die model is geevalueer en vergelyk met In Aanpasbare Monstering Interpolasietegniek (AMI). Daar is gevind dat die neurale netwerk minder akkuraat is as die AMI terwyl die koste aan ontwikkelingstyd en gebruikerstoesig hoer is.

Master of Science
Department of Electrical and Computer Engineering
Punit Prakash
Thermal therapies employing interstitial microwave applicators for hyperthermia or ablation are in clinical use for treatment of cancer and benign disease in various organs. However, treatment of targets in proximity to critical structures with currently available devices is risky due to unfocused deposition of energy into tissue. For successful treatment, complete thermal coverage of the tumor and margin of surrounding healthy tissue must be achieved, while precluding damage to critical structures. This thesis investigates two approaches to increase precision of microwave thermal therapy. Chapter 2 investigates a novel coaxial antenna design for microwave ablation (MWA) employing a hemi-cylinderical reflector to achieve a directional heating pattern. A proof of concept antenna with an S₁₁ of -29 dB at 2.45 GHz was used in ex vivo experiments to characterize the antennas’ heating pattern with varying input power and geometry of the reflector. Ablation zones up to 20 mm radially were observed in the forward direction, with minimal heating (less than 4 mm) behind the reflector. Chapter 3 investigates the use of magnetic nanoparticles (MNP) of varying size and geometry for enhancing microwave tissue heating. A conventional dipole, operating at 2.45 GHz and radiating 15 W, was inserted into a 20 mm radius sphere of distributed MNPs and heating measurements were taken 5 mm, 10 mm, and 15 mm radially away. A heating rate of 0.08°C/s was observed at 10 mm, an increase of 2-4 times that of the control measurement. These approaches provide strong potential for improving spatial control of tissue heating with interstitial and catheter-based microwave antennas.

With the rapid development of the modern technology, radio frequency and microwave systems are playing more and more important roles. Since the time the first microwave device was invented, they have been leading not only the military but also our daily life to a new era. In order to make the devices have more practical applications, more and more strict requirements have been imposed. For example, good adaptability, reduced cost and shrank size are highly required. In this thesis, three devices are designed based on this requirement. At first, a symmetric four-port microwave varactor based 90-degree directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. Then, a novel reconfigurable 3-dB directional coupler is presented. Varactors and inductors are loaded to the device to realize the reconfigurable performance. By adjusting the voltage applied to the varactors, the proposed coupler can be reconfigured from a branch-line coupler (90-degree coupler) to a rat-race coupler (180 degree coupler) and vice versa. At last, two types (Type-I and Type-II) of microwave baluns with generalized structures are presented. Different from the conventional transmission-line-based baluns where λ/2 transmission lines or λ/4 coupled lines are used, the proposed baluns are constructed by transmission lines with arbitrary electrical lengths.

Full wave analysis of microstrip lines at microwave frequencies is performed by using method of moments in conjunction with closed-form spatial domain Green&rsquo
s functions. The Green&rsquo
s functions are in general Sommerfeld-type integrals which are computationally expensive. To improve the efficiency of the technique, Green&rsquo
s functions are approximated by their closed-forms. Microstrip lines are excited by arbitrarily located current sources and are terminated by complex loads at both ends. Current distributions over microstrip lines are represented by rooftop basis functions. At first step, the current distribution over a single microstrip line is calculated. Next, the calculation of the current distributions over coupled microstrip lines is performed. The technique is then, applied to directional couplers. Using the current distributions obtained by the analysis, the scattering parameters of the structures are evaluated by using Prony&rsquo
s method. The results are compared with the ones gathered by using simulation software tools, CNL/2&trade
and Agilent Advanced Design System&trade
(ADS).

Un nombre croissant de données satellitaires et aéroportées acquises dans le domaine micro-ondes sur la surface demer est aujourd’hui disponible. L’interprétation correcte de ces observations dépend d’une part de la précision desmodèles de diffusion électromagnétiques, et d’une autre part de la maîtrise des propriétés hydrodynamiques etstatistiques de la surface. Ces dernières années ont connu une amélioration considérable des modèlesélectromagnétiques et spectraux. Cependant, certains phénomènes sont encore mal compris et non pris en comptepar ces modèles. En particulier, la variation angulaire de la surface de mer est à ce jour non totalement caractériséeet modélisée. Ce travail de thèse concerne l’étude de cette variation azimutale et des asymétries directionnelles de lasurface de mer. Une première étape consiste à effectuer une analyse expérimentale en se basant sur les données dela littérature mais également sur d’autres jeux de données acquises par l’ONERA et le DSTO. Cette analysepermettra de caractériser les asymétries directionnelles en fonction de la géométrie d’observation, l’état de mer et lafréquence électromagnétique. Une seconde étape consiste à proposer des mécanismes physiques pouvant être àl’origine des asymétries directionnelles. L’asymétrie upwind-crosswind étant essentiellement liée à la fonctiond’étalement du spectre directionnel, notre étude théorique a principalement porté sur la caractérisation del’asymétrie upwind-downwind. Nous étudions l’influence de la prise en compte des formes déferlantes, initialementà travers des formes simples de vagues fortement asymétriques, et ensuite à travers une distribution de pentesexpérimentale prenant en compte ces formes de vagues. Les asymétries obtenues par un modèle deux-échellesprenant en compte ces formes de vagues sont en accord qualitatif avec les asymétries observées pour les bandes defréquences X et L. Une étape supplémentaire consiste ensuite à calculer les asymétries obtenues par un code dediffusion rigoureux sur des profils numérisés d’une expérience en soufflerie et permet la validation des résultatsobtenus avec un modèle deux-échelles
An increasing number of airborne and spaceborne data acquired in the microwave regime on the sea surface is nowavailable. The appropriate interpretation of these observations depends on the precision of the electromagneticscattering models as well as the knowledge of hydrodynamic and statistical properties of the sea surface. Aconsiderable improvement has been realized in electromagnetic and spectral models in the recent years. However,some phenomena are still poorly understood and not correctly taken into account in these models. In particular, theangular variation of the sea surface is still not totally characterized and modeled. This PhD work concerns the studyof this azimuthal variation and the related directional asymmetries. A first step consists in carrying out anexperimental analysis based on data of the literature and other datasets acquired by ONERA and DSTO. Thisanalysis enables the characterization of the directional asymmetries with respect to acquisition geometry, sea stateand electromagnetic frequency. A second step consists in suggesting and testing physical mechanisms that may beat the origin of these directional asymmetries. As the upwind-crosswind asymmetry is essentially related to thespreading function of the directional spectrum, our theoretical study focused on the study of the upwind-downwindasymmetry. We investigate the influence of the presence breaking waves, initially through simple forms of stronglyasymmetric waves, and then through an experimental slope distribution including these wave forms. Theasymmetries obtained by a two-scale model taking into account these wave forms are in qualitative agreement withthe asymmetries observed at X and L bands. A further step consists in calculating the asymmetries using a rigorousmodel on digitized wind tank experiment profiles and allows the validation of the results previously obtained usinga two-scale model

Les systèmes de télécommunications requièrent de plus en plus l’utilisation des composants passifs hyperfréquences. La commercialisation de ces composants nécessite la miniaturisation de leurs tailles, l’augmentation de leurs performances et la réduction de leurs coûts. Parmi ces composants passifs, nous citons le coupleur directionnel qui est un quadripôle destiné à répartir la puissance sur deux ports de sortie, le quatrième port reste isolé. Les travaux relatés dans ce manuscrit ont pour objectifs la conception et la réalisation d’un coupleur à accès coplanaires obtenu à partir d’un résonateur auquel nous avons appliqué des lignes de couplage. Un modèle équivalent approché a été mis en évidence par un logiciel de simulation circuit. Une étude paramétrique a été réalisée à l’aide d’un logiciel électromagnétique 3D pour fixer une règle de conception qui permet un dimensionnement convenable du composant pour un intervalle de fréquences prédéfinies. Un fonctionnement bi-bandes a été exploité pour chaque raccordement de la fréquence. Une deuxième structure de couplage a été déduite en reliant directement les lignes couplées sur le résonateur. Une étude paramétrique ainsi qu’une règle de conception ont mis en évidence un fonctionnement de coupleur mono-bande de cette structure à des fréquences prédéfinies. Une troisième structure qui fonctionne en coupleur a été exploitée en remplaçant le filtre résonateur par deux circuits en méandres. Ce nouveau coupleur à méandres présente des bandes passantes assez larges ainsi qu’un fonctionnement possible en bi-bandes. Ces coupleurs mis en œuvre peuvent assurer un couplage de l’ordre de 3 ; 6 ; 8 et 10 dB et d’un déphasage entre les deux ports de sortie de 180° pour les deux premières structures et de 90° pour le coupleur à méandres. Plusieurs séries de prototypes sont ensuite fabriquées à partir des structures optimisées en simulation. Les caractérisations hyperfréquences de ces composants montrent la performance des dispositifs réalisés
Telecommunications systems require more use of passive microwave components. The commercialization of these components requires the miniaturization of their size, increasing their performance and the reduction of their costs. Among these passive components we cited the directional coupler which is designated to spread the power between two outputs, the fourth port being isolated. The ambition of this work is to study and fabricate a coupler with coplanar access obtained from a resonator where we applied coupling lines. An equivalent approximate model was obtained using circuit simulation software. A parametric study was made using 3D electromagnetic software to fix a design rule that allows a suitable design for the component in a predefined frequency range. Dual-band operation has been exploited for each frequency. A second coupling structure was deduced by directly connecting the coupled lines to the resonator. A parametric study and a design rule have shown the operation of this structure as a single band coupler at predefined frequencies. A third structure which operates like a coupler has been exploited by replacing the resonator filter by two meandering circuits. This new meandering coupler presents a wide bandwidth and a possible operating in dual-band. These implemented couplers provided a coupling factor of 3, 6, 8 and 10 dB and a phase shift between the two output ports of 180° for the two first structures and a 90° phase shifter for the meandering coupler. Several sets of prototypes are then made. The microwave characterizations show the performance of the fabricated device

Dielectric High-frequency transmission lines are natural alternative to the lines made of metal in term of low loss. These lines are mainly used in microwave techniques of measuring. The main object is to describe basic parameters of metal and dielectric transmission lines and their comparison. Next point is a basic overview of the excitation the lines from metal and it's application on dielectric transmission lines. Then make the simulation of microstrip directional couplers and coupler made by dielectric waveguides. The last point of work is construction these directional couplers and measuring their most important parameters.

L'intégration des nouveaux éléments basés sur la physique des plasmas dans le domaine des circuits et des systèmes micro-ondes est l'objectif de ce travail. En profitant des caractéristiques électromagnétiques des plasmas et en jouant sur leur architecture, on développe des micro-commutateurs micro-ondes et d'autres circuits radio et hyperfréquences en technologies microrubans ou en guide d'onde… La simulation de la propagation des ondes électromagnétiques dans un plasma et les études de l'interaction entre un plasma et les ondes électromagnétiques nécessite la connaissance des paramètres fondamentaux du plasma comme la permittivité. C'est pour cela qu'on étudie aussi les mesures plasmas par différents techniques comme la transmission/réflexion des ondes électromagnétiques, la perturbation des cavités résonnantes, ... Un schéma électrique équivalent modélisant un micro-commutateur hyperfréquence en plasma, est obtenu grâce aux mesures des courants de décharge électrique, à la rétro-simulation et aux techniques de modélisation numérique. Un coupleur directif hybride compact est utilisé pour les mesures plasmas en assurant la protection du matériel et de l'équipement de mesure des signaux d'un plasma.

This dissertation presents the investigation of antennas with improved performances at microwave frequencies. It covers the following three topics: the study of the metamaterial with near-zero index of refraction and its application in directive antenna design, the design technique of a wideband circularly polarized patch antenna for 60GHz wireless application and the investigation of a novel direction of arrival (DOA) estimation technique inspired by human auditory system. First, the metamaterial composed of two-dimensional (2-D) metallic wire arrays is investigated as an effective medium with an effective index of refraction less than unity (n(eff) < 1). The effective medium parameters (permittivity ε(eff), permeability μ(eff) and n(eff)) of a wire array are extracted from the finite-element simulated scattering parameters and verified through a 2-D electromagnetic band gap (EBG) structure case study. A simple design methodology for directive monopole antennas is introduced by embedding a monopole within a metallic wire array with n(eff) < 1 at the antenna operating frequencies. The narrow beam effect of the monopole antenna is demonstrated in both simulation and experiment at X-band (8 – 12 GHz). The measured antenna properties including return loss and radiation patterns are in good agreement with simulation results. Parametric studies of the antenna system are performed. The physical principles and interpretations of the directive monopole antenna embedded in the wire array medium are also discussed. Second, a fully packaged wideband circularly polarized patch antenna is designed for 60GHz wireless communication. The patch antenna incorporates a diagonal slot at the center and features a superstrate and an air cavity backing to achieve desired performances including wide bandwidth, high efficiency and low axial ratio. The detailed design procedure of the circularly polarized antenna, including the design of the microstrip-fed patch antenna and the comparison of the performances of the antenna with different feeding interfaces, is described. The experimental results of the final packaged antenna agree reasonably with the simulation results. Third, an improved two-antenna direction of arrival (DOA) estimation technique is explored, which is inspired by the human auditory system. The idea of this work is to utilize a lossy scatter, which emulates the low-pass filtering function of the human head at high frequency, to achieve more accurate DOA estimation. A simple 2-monopole example is studied and the multiple signal classification (MUSIC) algorithm is applied to calculate the DOA. The improved estimation accuracy is demonstrated in both simulation and experiment. Furthermore, inspired by the sound localization capability of human using just a single ear, a novel direction of arrival estimation technique using a single UWB antenna is proposed and studied. The DOA estimation accuracies of the single UWB antenna are studied in the x-y, x-z and y-z planes with different Signal to Noise Ratios (SNR). The proposed single antenna DOA technique is demonstrated in both simulation and experiment, although with reduced accuracy comparing with the case of two antennas with a scatter in between. At the end, the conclusions of this dissertation are drawn and possible future works are discussed.

A direction of arrival (DoA) estimation technique for broadband microwave signals is proposed using a single ultrawideband antenna. It is inspired by the sound source localization ability of a human auditory system using just one ear (monaural localization). By exploiting the incident angle-dependent frequency response of a wideband antenna, the DoA of a broadband microwave signal can be estimated. The DoA estimation accuracies are evaluated for two antenna configurations and microwave signals with different signal-to-noise ratios. Encouraging the DoA estimation performance of the proposed technique is demonstrated in both simulation and experiment.

Thesis (Ph.D.)--University of Mississippi, 2009.
Typescript. Vita. "April 2009." Dissertation director: Ahmed A. Kishk Includes bibliographical references (leaves 187-195). Also available online via ProQuest to authorized users.

Dès lors que des éléments rayonnants sont placés à proximité les uns des autres, comme c'est le cas au sein des antennes réseaux à balayage électronique, des interactions électromagnétiques parasites se créent entre eux. Ces couplages se manifestent par une perturbation des répartitions de courants des sources du réseau. Leur impact dépend fortement de l'angle de dépointage du réseau mais est généralement néfaste, car ils modifient les caractéristiques du rayonnement des sources. Les différents objectifs de compacité et les spécifications de performances radioélectriques visés pour les radars aéroportées peuvent conduire à des structures qui supportent et favorisent ces phénomènes de couplages parasites, sous la forme d’ondes d’espace et de surface. Ces derniers peuvent aller jusqu'à entrainer l'impossibilité pour l'antenne de rayonner dans certaines directions et à certaines fréquences d’utilisation : on parle de directions aveugles. Ce phénomène limite de manière considérable le volume de dépointage opérationnel d'un système radar. La maîtrise du couplage entre les éléments rayonnants est donc l'une des problématiques essentielles du développement et du dimensionnement d'une antenne réseau. La recherche qui traite de ce sujet n'en est plus à ses débuts (les premiers radars à balayage électronique sont exploités depuis les années 50) mais reste toujours en attente de solutions innovantes permettant de mieux comprendre et maîtriser ces phénomènes. Dans cette thèse, plusieurs méthodes permettant de minimiser les effets du couplage dans les réseaux à balayage électroniques ont été investiguées. Les travaux s'orientent notamment autour du défi de réduire les conséquences des directions aveugles sans modifier la maille initiale du réseau d'antenne (contrainte iso-maille)
When radiating elements are located close to one another, as it is the case in electronically phased array antennas, parasitic electromagnetic interferences occur between them. The impact of these coupling mechanisms depends to a large extent on the scanning angle of the array, but is usually harmful, since it alters the radiating properties and the active input impedance of the sources. The compactness objectives and radioelectric performances required for airborne radars can lead to structures that support and foster these parasitic couplings, in the form of surface or space waves. In some cases, mutual coupling can even result in the impossibility for the array to radiate in certain directions and at certain frequencies. This phenomenon, referred to as scan blindness, significantly reduces the operating scan volume of a radar system. In that respect, the control of coupling mechanisms between radiating elements is a major issue when developing an array antenna and although the research that deals with this subject is no longer in its infancy, it is always pending for new and innovating solutions to master these phenomena. In this thesis, different solutions enabling to minimize the effect of couplings in phased arrays are investigated. The presented research revolves around the challenge of limiting scan blindness consequences without modifying the initial mesh of the array antenna

碩士
長庚大學
電子工程學系
102
Although wireless communication products become more and more matured, however, RF wireless modules still play an important role. The system requires the RF circuits with better performance for satisfying the systems adopting the data transformation method. The RF power amplifier (PA) is one of the RF blocks that consumed the most of power of the system and affects the performance of the transceiver module directly. In general, the power amplifier has to be maintained its linearity for working properly when the output power goes to the high power state, thus it has to maintain the higher back-off to have good performance as the output power is slight lower than the power saturation state. There have been a variety of technical methods proposed to improve the efficiency of PA, but Doherty power amplifier became the popular technical method for it having the relatively simple structure and been proposed to have various methods of performance improving design and low production costs. In this paper, we proposed a new structure for designing the Doherty PA. Firstly, we replace the traditional power divider with the trans-directional (TRD) coupler to divide the power of the input signal into the different power ratio. Then, TRD coupler is adopted to design a new type of impedance converter and then use as adjustable power dividers to improve the efficiency. This paper uses commercial PCB material and ADS electromagnetic simulation software to develop a Doherty power amplifier which is working in 2GHz. In the case of using 3.5V power supply, the PA can deliver the output power of 25dBmassociate with the gain of 10dB and the power efficiency of 52%. In the case of power back-off 5dB, this Doherty amplifier power efficiency can still reach 44%. Then we use the previously mentioned the new type converter and adjustable power dividers to realize an adjustable input power ratio and different output matching networks of Doherty amplifiers to improve the characteristics of PA. It is found the new type of PA can still deliver the output power of 25dBm and 53%power efficiency, that are almost same as that using traditional structure, but the new Doherty PA can increase the output power to 5dBmat back-off region and thus increase the power efficiency of this Doherty PA up to 52% that is 8% improvement as compared with the traditional type. On the other hand, the adjustable Doherty power amplifier can reach the best efficiency by adjusting the input power ratio of carry amplifier and peaking amplifier.

碩士
長庚大學
電子工程學系
100
Conventional microwave balanced amplifier can increase its output power and provide very good impedance matching at its input and output ports. Thus, it is easy to connect with other circuits and eliminate the use of extra components to achieve the desired impedance matching. Since the traditional microwave amplifier is usually composed by branch line coupler and thus it need to be implemented with large circuit area. To improve this disadvantage, we propose a new feature of the balanced amplifier that uses the trans-directional microwave couples to realize the balanced amplifier in this thesis. This kind of balanced amplifier can provide several advantages as compared with conventional structure. First, it allows the amplifiers in the balances amplifiers to share the same DC bias circuitry and eliminate the need of DC blocking capacitors with placing the trans-directional couplers instead of the branch-line couplers in the conventional structure. Secondly, it will also reduce the required area for realizing a balanced amplifier. However, the proposed new structure still keep the same advantages of traditional balanced amplifier such as increased output power and input and output impedance matching function. For verifying the proposed circuit structure and design theory, we designed a balanced amplifier to operate at 2.4GHz for the commercial WLAN applications. It is a two stage design and constructed on the FR4 PCB circuit board with using some surface mount components and two bipolar transistors. This circuit has size 43mm6mm. The measurement of the prototype shows the maximum output power can reach 25.75dBm and input and output return loss all below 20dB within the frequency band of interest. The required power consumption is about 0.18W.

在現代通信系統，無線服務的需求不斷增加，帶動了通信系統，支持多標準的操作需要。 雙波段或多波段操作幾乎都是必要的，能夠提供這些操作的微波器件已成為減小尺寸和降低成本有吸引力的解決方案。
分支線耦合器是用於微波和毫米波應用的最流行的無源電路之一。它們通常用於平衡放大器和混頻器去實現良好的回波損耗以及隔離。其中一個至關重要的部份是設計一個可以靈活作多波段分配的分支線耦合器。
傳統上，完全平面的實施，雙波段分支線耦合器可以通過短截線，階梯阻抗線，耦合線等不同的分佈式結構實現。不同的設計方案已在這幾年來出現。窄帶操作和複雜的電路設計，是以前的設計的主要缺點。雖然，在理論上，多節技術可以拓寬帶寬，但它的主要缺點是電路的面積變大了及使用極端低/高傳輸線阻抗。因此，它不是一個大量和低成本生產的解決方案。
在這項研究中，設計了全新的並增強了性能的雙波段分支線耦合器(零分貝和三分貝的功率分裂)。這些設計能在兩個指定的頻帶有不平等的工作帶寛。通過正確選擇雙頻四分之一波長阻抗變換器的電氣長度和線路阻抗，傳輸相位斜率將能夠被控制並給出帶寬不對稱的特點，其性能可以進一步擴展，涵蓋了廣泛的應用。
以上所有設計都只需要單層線路版的制作及可實現的傳輸線阻抗。應用奇/偶模式分析所給出設計公式。這些設計具有低損耗，佈局靈活，緊密的尺寸大小的特性。這些設計己經使用標準微帶的結構實現其特點，其結果得到了實驗結果的進一步驗證。分支線耦合器只需要更小的節數就能實現相同的性能。
In modern communication systems, the increasing demand for wireless services has driven the need for communication systems that support multi-standard operations. Dual-/Multi- band operation is almost a necessity and the adoption of microwave multi-band devices has become an attractive solution towards size and cost reduction of RF frontend designs.
Branch-line coupler is one of the most popular passive circuits used for microwave and millimeter-wave applications. They are commonly used in balanced amplifiers, phase-shifter, mixer and frequency multipliers for achieving good return loss, as well as isolation. It is therefore essential to have a branch-line coupler with multi-band operation.
Traditionally, for fully planar implementation, the construction of dual-band branch-line couplers are usually accomplished by distributed structures based upon shunt-stub, stepped-impedance line, coupled line etc. Narrow-band operation and circuit complexity are the major drawbacks for these previous designs. Although, in theory, the available bandwidth may be broadened by multi-section configurations, its major tradeoffs are the enlarged circuit size as well as the extreme line dimensions involved. Therefore, it is not preferable to mass and low cost production.
In this research, advanced designs of dual-band branch-line coupler (0 dB and 3 dB power splitting) with enhanced performances are presented. By proper selection of the number of sections, electrical lengths and line impedances of appropriate branch-lines of the coupler, its performance can be further extended to cover a wide range of applications.
All the proposed circuits require only single-layer fabrication and realizable line impedance. Closed form design formulas are made available by the application of even/odd- mode formulation. They feature low loss, flexible layout and compact size. The designs have been implemented and characterized using standard microstrip, and verified experimentally.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Yeung, Sung.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 92-95).
Abstracts also in Chinese.
Abstract --- p.ii
摘要 --- p.iii
Acknowledgement --- p.iv
Table of Content --- p.v
Lists of Figures --- p.viii
Lists of Tables --- p.xii
Chapter Chapter 1 --- : Introduction --- p.1
Chapter 1.1 --- Research Motivation and Objective --- p.1
Chapter 1.2 --- Original Contribution --- p.3
Chapter 1.3 --- Research Approach, Assumptions and Limitations --- p.4
Chapter 1.4 --- Overview of the Thesis Organization --- p.5
Chapter Chapter 2 --- : Review of Microwave Coupler Design --- p.6
Chapter 2.1 --- Coupler Design Fundamental --- p.6
Chapter 2.1.1 --- Coupler Design with Equal Power Splitting --- p.7
Chapter 2.1.2 --- Coupler Design with Unequal Power Splitting --- p.12
Chapter 2.1.3 --- 0-dB Coupler or Crossover --- p.16
Chapter 2.1.4 --- Coupler Design with Size Miniaturization --- p.18
Chapter 2.1.5 --- Wide Band Coupler Design --- p.21
Chapter 2.2 --- Dual-Band and Multi-Band Branch-line Coupler --- p.25
Chapter 2.2.1 --- Dual-Band Couplers Based on Composite Right/Left-Handed Transmission Line --- p.25
Chapter 2.2.2 --- Dual-Band Couplers with Shunt Stubs --- p.28
Chapter 2.2.3 --- Dual-Band Coupler Based on Stepped-Impedance-Stub-Line --- p.30
Chapter 2.2.4 --- Dual-Band Coupler with Port Extensions --- p.33
Chapter 2.2.5 --- Tri-Band Coupler Based on Matching Network --- p.35
Chapter 2.2.6 --- Multi-passband Branch-line Coupler Design --- p.37
Chapter 2.3 --- Summary --- p.39
Chapter Chapter 3 --- : A Novel Dual-band 0-dB Branch-line Coupler Design --- p.40
Chapter 3.1 --- Proposed Circuit --- p.40
Chapter 3.2 --- Analysis of Single-band 0-dB Branch-line Coupler --- p.43
Chapter 3.3 --- Single- to Dual-band Conversion --- p.52
Chapter 3.4 --- Experimental Results --- p.55
Chapter 3.5 --- Summary --- p.58
Chapter Chapter 4 --- : A Novel Dual-band 3-dB Branch-line Coupler with Unequal Bandwidth --- p.59
Chapter 4.1 --- Proposed Dual-band Impedance Transformer: --- p.59
Chapter 4.2 --- Single-band 3-dB Coupler Design --- p.65
Chapter 4.3 --- Dual-band 3-dB Coupler Design --- p.70
Chapter 4.4 --- Experimental Results --- p.76
Chapter 4.4.1 --- Equal bandwidth design --- p.76
Chapter 4.4.2 --- Unequal bandwidth design --- p.78
Chapter 4.5 --- Summary --- p.81
Chapter Chapter 5 --- : A Novel Dual-band 0-dB Branch-line Coupler Design with Unequal Bandwidth --- p.82
Chapter 5.1 --- Proposed Circuit --- p.82
Chapter 5.2 --- Analysis and Formulation --- p.84
Chapter 5.3 --- Simulation Results --- p.85
Chapter 5.4 --- Experimental Results --- p.87
Chapter 5.5 --- Summary --- p.89
Chapter Chapter 6 --- : Conclusion and Recommendation for Future Work --- p.90
Chapter 6.1 --- Conclusion --- p.90
Chapter 6.2 --- Recommendation for future work --- p.91
References --- p.92
Author’s Publications --- p.96
Chapter Appendix 1: --- Brief Summary of Design Approaches of Hybrids Couplers --- p.97
Chapter Appendix 2: --- Transformation between S- and ABCD- parameters for two-port network --- p.99

For size miniaturization and cost reduction, the design of dual band devices has become an emerging research area in recent years. A desirable dual-band solution should offer size compactness, high performance (e.g. low insertion loss) and compatible with conventional printed circuit broad (PCB) technology, especially microstrip lines.
In this research, several new devices, including rat-race coupler, power divider and crossover junction, capable of operating at dual frequency bands are proposed. These structures involve only simple branch-line sections and a minimal number of shunt stubs. All characteristic impedances are ranged from 20 O to 100 O. Most designs can operate with wide frequency spacing between the two bands. These designs offer low insertion loss as well as good return loss performances, and are small in size, in compared to the broadband approach. For design purposes, explicit closed-form equations are derived for the evaluation of circuit parameters. In addition, the usable range of these devices with respect to frequency band separation is examined. For verification, various prototypes are constructed by using microstrip technology and in-house fabrication facilities. Both simulated and measured results are presented and compared with state-of-the-art examples.
Microwave passive couplers are widely used in microwave and millimeter-wave applications and communication systems. Common examples are branch line coupler, rat race coupler, power divider, and crossover junction. They are used for the dividing, combining and re-directing of signal power.
Very often, a passive coupler utilizes simple quarter-wavelength transmission lines for implementation which will lead to narrow-band operation. Therefore, it is difficult to deploy such circuit for wide-band or multi-band applications. Multi-section topologies may be used to broaden the operating bandwidth, with which the major drawbacks are enlarged circuit size and the requirement of extreme high (or low) branch-line characteristic impedances. Both are not attractive for mass and low cost production. Conventional design approaches are, therefore, not suitable for modern communication systems with multi-band operation.
Wong, Fai Leung.
Adviser: Michael Cheng.
Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: .
Thesis (Ph.D.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 118-122).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.

This thesis presents the design of radio-frequency (RF) tunable active inductors (TAIs) with independent inductance (L) and quality factor (Q) tuning capability, and their application in the design of RF tunable phase shifters and directional couplers for wireless transceivers. The independent L and Q tuning is achieved using a modided gyrator-C architecture with an additional feedback element. A general framework is developed for this Q- enhancement technique making it applicable to any gyrator-C based TAI. The design of a 1.5V, grounded, 0.13um CMOS TAI is presented. The proposed circuit achieves a 0.8nH-11.7nH tuning range at 2GHz, with a peak-Q in excess of 100. Furthermore, printed and integrated versions of tunable positive/negative refractive index (PRI /NRI) phase shifters, are presented in this thesis. The printed phase shifters are comprised of a microstrip transmission-line (TL) loaded with varactors and TAIs, which, when tuned together, extends the phase tuning range and produces a low return loss. In contrast, the integrated phase shifters utilize lumped L-C sections in place of the TLs, which allows for a single MMIC implementation. Detailed experimental results are presented in the thesis. As an example, the printed design achieves a phase of -40 to +34 degrees at 2.5GHz. As another application for the TAI, a reconfigurable CMOS directional coupler is presented in this thesis. The proposed coupler allows electronic control over the coupling coefficient, and the operating frequency while insuring a low return loss and high isolation. Moreover, it allows switching between forward and backward operation. These features, combined together, would allow using the coupler as a duplexer to connect a transmitter and a receiver to a single antenna. Finally, a planar electronically steerable patch array is presented. The 4-element array uses the tunable PRI/NRI phase shifters to center its radiation about the broadside direction. This also minimizes the main beam squinting across the operating bandwidth. The feed network of the array uses impedance transformers, which allow identical interstage phase shifters. The proposed antenna array is capable of continuously steering its main beam from -27 to +22 degrees of the broadside direction with a gain of 8.4dBi at 2.4GHz.

Two new variations on traditional microwave resonant cavity surface resistance measurements of high temperature superconductors are presented. A new cavity perturbation technique is developed for the measurement of T1₂Ba₂CuO₆±[delta] (Tl-2201) single crystals, and preliminary measurements are presented for uniquely prepared YBa₂Cu₃OD₆₊̮̮y single crystals in which a non-local normal fluid response is expected. The resonant cavity probe designed for measurement of T1-2201 single crystals operates in the TMolo mode such that the sample is located at a magnetic field node and electric field antinode. A dual-sapphire hot-finger technique was developed for supporting the sample in the electric field of the cavity, and non-perturbative issues associated with this technique were addressed. A dielectric layer resulting from the degradation of sample outer surfaces was identified as a significant source of dielectric loss. The dimensional dependence of this loss was treated theoretically and etching was shown to drastically reduce this unwanted absorption. The factor currently limiting use of this probe to measure T1-2201 single crystals is absorption by the optical-grade sapphire used to support the sample in the cavity. The loss due to the sapphire is currently on the same order of magnitude as the sample loss to be measured. Employment of premium-grade sapphire plates should significantly reduce this background level and permit accurate measurement of the surface resistance of single crystal T1-2201. YBaD₂Cu₃O₆+y, single crystals have been meticulously prepared with large ;-axis dimensions. This has permitted microwave surface resistance measurements where a magnetic field is applied perpendicular to the CuOz planes, while minimizing demagnetization effects. In this geometry, the electrodynamic response of the normal fluid is expected to be non-local, as the mean free path of the quasiparticles exceeds the penetration depth. R₃(T) measurements were obtained for the crystals using a resonant cavity operating in the TE₀₁₁ mode at 13.4 GHz. No increase in the surface resistance, which is expected for a non-local quasiparticle response, was observed at low temperatures. Possible explanations for this result, and recommendations for further study of these samples are discussed.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

The mobile data market in South Africa is predicted to be a significant revenue contributor for mobile telecommunication operators, such as MTN, over the next five years. In light of the declining revenue from the traditional voice services, most operators worldwide are turning to mobile data as the solution to this problem. However, there is widespread confusion on which is the correct business model to implement in order to maximise the gains from this new market. To add to the complexity, there is also no clear cut technology upgrade path. While it is well understood that the main driver for the mobile data market will be high data throughputs, the industry is still unsure on which is the best route for an operator to follow as it moves from a second generation (2G)to a third generation (3G) network. This dissertation discusses the business model that MTN should implement in order to become the market leader for mobile data in South Africa. A literature survey on the latest market characteristics and forecast for the mobile data industry is presented. The recent developments on mobile data business models is also discussed. The technology upgrades, i.e. GPRS, EDGE and UMTS, available to a mobile telecommunication operator is described in detail. GPRS is the first stage in the evolution from a 2G to a 3G network and offers data rates of 40 Kb/s. EDGE improves on the GPRS technology with data speeds of 59.2 Kb/s per timeslot and utilise the same frequency, radio and switching equipment. UMTS is the final stage and is capable of delivering 2 Mb/s data rates. It operates on a different frequency spectrum, thus, requiring a new licence from the telecommunications regulator. In order to develop a new business model, MTN's current GPRS model is analysed. The poor success rate of this model can be attributed to the high prices being charged for the services and the lack of any "killer applications" to entice the users. The business model focuses on the customer value of service, organisational, technical and pricing models. For the customer value of service, it is shown that MTN must offer cheaper prices for the services, higher data rates and more exciting applications. The pre-paid subscribers should also be allowed access to the mobile data network. The main changes to the organisational arrangement in MTN includes creating sub-departments in marketing, sales and network group to focus solely on mobile data. MTN must develop an integrated services approach and this can only be achieved by developing partnerships with all key players in the mobile data industry, such as content providers and application developers. Due to the high costs, the technology arrangement section proposes that MTN first upgrade the network to be EDGE capable and later implement a UMTS network. The financial arrangement discusses the revenue, pricing and cost model. The revenue model proposes the development of an exciting and attractive mobile portal. New services and applications such as mobile gaming and gambling must be created for the personal consumers. For the corporate consumers, applications and services must be developed for customer relation management, supply chain management and workforce application. A hybrid pricing model must be adopted. A fixed, metered and value based pricing structure should be implemented to make the services more affordable and to gain the maximum revenues. Finally, the various elements that constitute the cost model is examined. The major contributing costs for the operator will be the network upgrade and subscriber acquisition.
Thesis (MBA)-University of KwaZulu-Natal, 2004.

博士
長庚大學
電子工程學系
98
In this thesis, a novel trans-directional (TRD) coupler has been designed. Applications of quadrature voltage controlled oscillator (QVCO) and balun are presented and good performances are achieved. Compared with the traditional coupled-line and branch-line couplers, the TRD coupler uses a different kind of coupling mechanism. Various new applications should be worth to be investigated. At first, the required condition for TRD operation is derived. Then it shows how to realize the TRD coupling by periodically loading couple lines with shunt susceptances. Two kinds of the original and size-reduced prototypes are fabricated by single layer PCB technology at 3.6GHz. Good agreement with simulated results is reached. Next, a QVCO is realized by using the TRD couplers. The TRD couplers allow decoupling the DC path between input and output. Thus, they can eliminate off-chip biasing circuits. Since the quadrature signals are generated only by TRD couplers, the oscillator core can be optimized for circuit performance without considering the generation of quadrature signals. A Ka band QVCO fabricated in CMOS 0.18 um technology is designed. The measurement results of QVCO have -1.52 dBm output powers with less than 1 dB amplitude imbalance and less than 6° phase difference in the frequency range of 31.9 to 32.7 GHz. The best measured phase noise of the QVCO is -110.6 dBc/Hz at 1 MHz offset from the center frequency. Finally, a new type planar balun is proposed by using the TRD couplers. The syntheses and performances of the balun are derived and analyzed. No via-holes to ground are needed in the proposed balun which can decrease the phase errors caused by the inductive effects of via-holes. A new type of balun whose coupling is totally contributed by the capacitors is also discussed. It can make the composed lines of the balun routed in a small area to shrink the circuit size. Two prototypes are designed by single layer PCB technology. The first one is formed by -3 dB TRD couplers to achieve the best input matching results. The bandwidth is 1.93~2.67 GHz (32%). The second prototype is formed by -4.8 dB TRD couplers to shrink the dimension of the circuit to 16.8 mm × 39.4 mm. The bandwidth is within 380~460 MHz with the input return loss less than -11 dB, phase difference less than 1°, and amplitude imbalance is less than 0.16 dB.

碩士
中原大學
電機工程研究所
95
In the telecommunication liberalization process, each kind of new condition telecommunication service continues to open, the folk is day by day earnest to the frequency spectrum demand. American TCI/BR Corporation produces "8067" the receiver primarily, and electric wave of monitoring network union computer network constitution,To effectively grasps condition of the airborne electric wave use, achieves all the people to share "the radio resource". This report main content in the radio position finder function, the content divides into three parts：First partial introduction superheterodyne receiver and radio position finder principle of work and system overhead construction;The second part introduces the TCI 8,067 receivers principle of work and the system model introduction，In three partial introductions position finder the receiver work way and the overhaul method, then carry on the self- examination function (BITE) to complete the system the function test。The expectation from this fitness report completing, promotes our country merchant in the position finder maintenance and the overhaul ability, not original factory all sorts of limits and high quota maintenance cost.

博士
元智大學
通訊工程學系
105
This thesis proposes a novel modified cavity-back slot antenna (M-CBSA) which can be easily integrated with T/R module and applied to active array antenna used to estimate Direction-of-Arrival (DOA). The M-CBSA activates the cavity antenna in a different type of feeding structure. The RF circuits originally located on the aperture surface of each array antenna element is moved to the bottom surface of each cavity. This change can eliminate the interference on radiation pattern caused by the feeding circuit. This novel feeding structure can also decrease the depth of metal cavity, so as to lower the thickness and weight of whole array antenna. It is also verified by simulation and measurement that the bandwidth of the M-CBSA structure is wider than that of the traditional CBSA structure. Therefore, the M-CBSA structure can be a satisfying substitute of the back feed open end waveguide slot antenna which suffers from overweight because of over-deep metal cavity. In order to verify the DOA estimation property of array antenna composed of M-CBSA, the thesis includes the simulated and measured T/R radiation pattern of active array antenna composed of fourteen active submodules. Each active submodule includes thirty-two M-CBSA elements and corresponding T/R modules. It is verified that the M-CBSA structure is suitable to be integrated with high power T/R module and enables the active array antenna to possess well property of DOA estimation. Furthermore, in order to overcome the effect of unequal phase lengths of beamforming network (BFN) on the DOA estimation property of array antenna, this thesis also includes several advanced researches to enhance the properties of microwave components (power divider, mono-pulse comparator) in the BFN. These advanced researches includes equal output power and phase Wilkinson power dividers with output port numbers of six and seven, ring hybrids with identical output phases in operational bandwidth, mono-pulse comparator with identical output phases in operational bandwidth and directional couplers with any power ratios and identical output phase in a wide bandwidth. Especially, it is found in this thesis that the concept of Schiffman phase shifter can be ingeniously manipulated to let the ring hybrid achieve identical output phase in a given operational bandwidth. A wide band Schiffman 90° phase shifter is also integrated with directional coupler to achieve the design of equal phase output. The equal-output-phase ring hybrids proposed in this thesis possess better power handling capability (can be up to Kilo-Watts) than the Wilkinson power divider and can be further constituted to design mono-pulse comparator with wide band identical output phase. Besides, the directional coupler with identical output phase and any output power ratio can also be a good candidate of high power microwave component.