Recently, the advent of the integrated circuits (ICs), the monolithic microwave integrated circuits (MMICs) and the multiprocessing computer technology have provided numerous opportunities to make the radar technology compact and affordable. The ultra-wideband (UWB) technology gives many advantages over the traditional narrowband radar systems due to its high spatial resolution, low susceptibility to interference, superior penetration depths, and increased peak power. However, the ability to digitize and reconstruct the full UWB signal spectrum comes at a considerable cost and size. Ultimately, high-speed sampling rates above 10 giga-samples per second (GSPS) are beyond the abilities of conventional analog-to-digital converters (ADCs). The UWB technology is inaccessible to the end-user for various advanced applications in microwave imaging and detection. The purpose of this work is to provide a low-cost, dual-channel UWB pulsed-radar system that is readily available with a 1:10 system bandwidth. The advancements in low-cost alternatives for compact and portable designs empower many promising UWB applications. Here, the desired bandwidth is from 500 MHz to 5 GHz, which utilizes a fast pulse repetition frequency (PRF) in short-range applications. The preliminary results from the novel Equivalent-Time Sampling Receiver are promising with an equivalent-time sampling rate up to 20 GSPS. Nevertheless, the system design is versatile for bandwidth tuning in order to meet the needs of different applications. This versatility is enabled by: i) selection of the effective sampling rate through the field-programmable gate array (FPGA) programming environment, ii) choice of the receivers' front-end track and hold (T & H) amplifier bandwidth, iii) a collection of different PRFs from the low kilohertz up to 20 MHz, iv) tuning of the pulse generator bandwidth, and v) simultaneous multi-channel capabilities enabling antenna beam-forming, polarization diversity and spatial diversity. The result is a fully functional prototype that costs a fraction of traditional bench-top solutions. / Thesis / Master of Applied Science (MASc)

With the increasing demand on wireless and portable devices, the radio frequency front end blocks are required to feature properties such as wideband, high frequency, multiple operating frequencies, low cost and compact size. However, the current radio frequency system blocks are designed by combining several individual frequency band blocks into one functional block, which increase the cost and size of devices. To address these issues, it is important to develop novel approaches to further advance the current design methodologies in both space and spectrum domains. In recent years, the concept of artificial materials has been proposed and studied intensively in RF/Microwave, Terahertz, and optical frequency range. It is a combination of conventional materials such as air, wood, metal and plastic. It can achieve the material properties that have not been found in nature. Therefore, the artificial material (i.e. meta-materials) provides design freedoms to control both the spectrum performance and geometrical structures of radio frequency front end blocks and other high frequency systems. In this dissertation, several artificial materials are proposed and designed by different methods, and their applications to different high frequency components and circuits are studied. First, quasi-conformal mapping (QCM) method is applied to design plasmonic wave-adapters and couplers working at the optical frequency range. Second, inverse QCM method is proposed to implement flattened Luneburg lens antennas and parabolic antennas in the microwave range. Third, a dual-band compact directional coupler is realized by applying artificial transmission lines. In addition, a fully symmetrical coupler with artificial lumped element structure is also implemented. Finally, a tunable on-chip inductor, compact CMOS transmission lines, and metamaterial-based interconnects are proposed using artificial metal structures. All the proposed designs are simulated in full-wave 3D electromagnetic solvers, and the measurement results agree well with the simulation results. These artificial material-based novel design methodologies pave the way toward next generation high frequency circuit, component, and system design.

First-pass success is important for cost-effective Monolithic Microwave and Millimeter-wave Integrated Circuits (MMMICs) since additional iterations to the MMMIC design are costly and take months to complete. In order to meet these goals, new levels of capabilities in the design, test and comprehensive simulations are required. The MMMICs employ microstrip line as a component connecting transmission medium as well as a distributed matching element. In a circuit layout, any deviation from straight transmission lines causes the introduction of discontinuity parasitics which must also be modeled as accurately as possible in order to predict the circuit performance. These discontinuities should either be taken into account or compensated for at the final stage of the design. A comparative study of different circuit simulators is undertaken to characterize microstrip discontinuities. Several microstrip discontinuities, such as bends, steps, and tees are examined and optimum compensated models are determined. / Master of Science

In this dissertation, some multi-function and flexible RF/microwave devices have been studied to solve the issues in the modern microwave system designs. First, a power divider with two functions is proposed. The first function is a zero-phase delay power divider using zero-phase impedance transformer. The second function is a power divider with impedance transforming property. To achieve the first function, the two arms are treated as zero-phase impedance transformers. When the phase requirement is relaxed, the second function is obtained. Shunt transmission line stubs are employed to connect the isolation resistor, which provides great flexibility in the design. Then, a balun with transparent termination impedance and flexible open arms is designed. The design parameters of the balun are independent to the port impedance. This property allows the balun to work with different system impedances. Furthermore, the two output ports of the balun do not need to be connected together, which enables the device to have a very flexible structure. Finally, the continuous research of a tunable/reconfigurable coupler with equal output impedance is presented. In addition to the tunable/reconfigurable responses, unequal output impedance property is added to the microstrip line coupler. To shrink the size at the low frequency and make it easy for fabrication at higher frequency, the coupler is redesigned using lumped components. To validate the design theories, simulations are carried out. Moreover, prototypes of the power divider and the balun are fabricated and characterized. The simulation and measurement results match well with the theoretical calculation.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A complete mixed-potential integral equation formulation for the analysis of arbitrarily shaped scatterers in a planarly layered medium is presented. The integral equation is able to solve for simultaneous electric and magnetic surface currents using a Method of Moments (MoM) procedure. The MoM formulation which was developed uses vector-valued basis functions defined over a triangular mesh and are used to model electric currents on conducting scatterers and magnetic currents on slotline structures. The Green’s functions employed in the analysis were developed for a stratified medium using a Sommerfeld plane wave formulation. The scheme used for filling the method of moments matrix was designed to simultaneously solve multiple problems that are stacked and separated by an infinite conducting ground plane. The filling algorithm also efficiently packs partially symmetric matrices, which are present when solving problems that support a combination of electric and magnetic currents. Several examples are presented to illustrate and validate the analysis method. Numerical predictions of the scattering parameters (both magnitude and phase) show good correspondence with results from literature and measured data. / AFRIKAANSE OPSOMMING: ’n Volledige gemengde potensiaal integraalvergelyking formulering vir die analise van stralers van arbitrˆere vorm binne gelaagde strukture word aangebied. Die integraalvergelyking kan gelyktydige elektriese en magnetiese oppervlakstrome oplos deur die Metode van Momente (MoM) te gebruik. Die MoM formulering gebruik vektor basis funksies wat oor ’n driehoekige diskretisering gedefinieer word om elektriese strome op geleidende stralers en magnetiese strome op gleuflyn strukture te modelleer. Die Green’s funksies wat in die analise gebruik word, is ontwikkel vir gelaagde media deur gebruik te maak van Sommerfeld se platvlakgolf formulering. Die metode wat gebruik word om the moment matriks te vul, is ontwerp om meervoudige gestapelde probleme wat deur oneindig geleidende grondvlakke geskei word, gelyktydig op te los. Gedeeltelik simmetriese matrikse word ook effektief gevul. Hierdie matrikse kom voor wanneer probleme ’n kombinasie van elektriese en magnetiese strome ondersteun. Verskeie voorbeelde word gebruik om die analise metode te verifieer. Numeriese voorspellings van strooiparameters (beide grootte en hoek) vergelyk baie goed met resultate en gemete data wat in die literatuur gevind is. iv

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / High-temperature superconductive (HTS) logic has become a large research field worldwide. The HTS advantages compared to the low-temperature circuits are the reduced cooling requirements, increased or comparable operation speeds and the "ease" of manufacturing. The potential of HTS logic circuits is vast and surpassed by very few other technologies. However, before these circuits can reach the market, suitable simulation packages and fabrication processes have to be designed. The simulation of HTS Rapid Single Flux Quantum (RSFQ) circuits are performed at temperatures between 30 and 77 Kelvin. The noise sources in Josephson junctions (JJ’s) are investigated and incorporated into these simulations. The results show that it is possible to operate these circuits in this temperature range. An objective of this thesis is the fabrication of HTS step-edge JJ’s. A process to fabricate these junctions was investigated and improved. This includes the etching of substrate steps with the use of the argon ion mill, deposition of the YBCO thin films with the Pulsed Laser Deposition (PLD) system and the etching of the final circuit by the use of dry or wet etching.

Esta dissertação propõe uma metodologia de projeto de osciladores distribuídos controlados por tensão - DVCO - com realimentação reversa em freqüência de microondas. Estes constituem uma nova classe de osciladores recentemente proposta, a qual é obtida através da realimentação reversa de amplificadores distribuídos e tem como principal vantagem a possibilidade de sintonia em faixa ultra-larga de freqüência. São apresentados os fundamentos teóricos de operação do circuito e é proposta uma extensão da análise linear apresentada na literatura, considerando linhas de transmissão artificiais m-derivadas, a qual permite prever as transcondutâncias mínimas necessárias dos transistores e a freqüência inicial de oscilação. O método de projeto proposto é direcionado a DVCOs com realimentação reversa empregando transistores de efeito de campo dos tipos MESFET (Metal Semiconductor Field Effect Transistor) e PHEMT (Pseudomorfic High Electron Mobility Transistor), bem como ao uso de tecnologia de circuitos híbridos de microondas - MICs, e circuitos integrados monolíticos de microondas - MMICs. A metodologia proposta definiu critérios para implementar a topologia deste circuito através de componentes reais, considerando-se os parasitas associados aos mesmos. Para validação do procedimento de projeto, concebeu-se e simulou-se através do programa ADS da Agilent um oscilador intitulado DVCO 3 GHz, cuja faixa de freqüência especificada estende-se de 1 a 3 GHz e a potência mínima de saída especificada é de 10 dBm. Um protótipo foi construído em circuito híbrido e seus resultados experimentais foram comparados aos simulados. A freqüência de oscilação medida foi de 1,04 GHz a 3,05 GHz e a potência obtida esteve entre 9,8 e 14,3 dBm, apresentando boa concordância com as simulações. O ruído de fase foi medido entre 100 kHz e 1 MHz de distância da portadora, observando-se uma inclinação proporcional a 1/f3. Verificou-se que a diminuição da corrente de polarização Ids dos transistores, através da redução de sua tensão de polarização de porta-fonte Vgs, melhorou o ruído de fase. Na condição de polarização de menor ruído de fase, observaram-se valores entre -84 e -93 dBc/Hz a 100 kHz da portadora. / In this dissertation, a design methodology applied to microwave reverse feedback distributed voltage controlled oscillators - DVCO - is proposed. This circuit constitutes a new class of oscillators, obtained from reverse feeding back of the distributed amplifier. The main advantage of this topology is its capacity to achieve ultra-wideband frequency tuning. Circuit theoretical background is presented and an extension of the linear analysis presented in the literature is proposed. It allows predicting transistor minimum transconductances and the oscillation initial frequency, considering m-derived artificial transmission lines. The proposed design method is applicable to reverse feedback DVCOs employing field effect transistors MESFET (Metal Semiconductor Field Effect Transistor) and PHEMT (Pseudomorfic High Electron Mobility Transistor), as well as using MIC (Microwave Integrated Circuits) and MMIC (Monolithic Microwave Integrated Circuits) technology. The proposed methodology defined criterion to employ real components, considering the component parasitics. In order to validate the design method, an oscillator named DVCO 3 GHz was designed and simulated through software Agilent ADS, with specified band from 1 up to 3 GHz and minimum output power of 10 dBm. A prototype was implemented in hybrid circuit technology and the measurements were compared to the simulation results. The measured oscillation frequency varied from 1,04 GHz up to 3,05 GHz and the output power was 9,8 to 14,3 dBm, presenting good agreement with simulations. Phase noise was measured in the range between 100 kHz and 1 MHz shift from carrier; in which it was observed a 1/f3 slope. It was verified that decreasing the transistor bias current Ids through decreasing its gate bias voltage Vgs reduced phase noise. In the biasing condition for lowest phase noise, values between -84 and -93 dBc/Hz at 100 kHz off-set from carrier were measured.

Esta dissertação propõe uma metodologia de projeto de osciladores distribuídos controlados por tensão - DVCO - com realimentação reversa em freqüência de microondas. Estes constituem uma nova classe de osciladores recentemente proposta, a qual é obtida através da realimentação reversa de amplificadores distribuídos e tem como principal vantagem a possibilidade de sintonia em faixa ultra-larga de freqüência. São apresentados os fundamentos teóricos de operação do circuito e é proposta uma extensão da análise linear apresentada na literatura, considerando linhas de transmissão artificiais m-derivadas, a qual permite prever as transcondutâncias mínimas necessárias dos transistores e a freqüência inicial de oscilação. O método de projeto proposto é direcionado a DVCOs com realimentação reversa empregando transistores de efeito de campo dos tipos MESFET (Metal Semiconductor Field Effect Transistor) e PHEMT (Pseudomorfic High Electron Mobility Transistor), bem como ao uso de tecnologia de circuitos híbridos de microondas - MICs, e circuitos integrados monolíticos de microondas - MMICs. A metodologia proposta definiu critérios para implementar a topologia deste circuito através de componentes reais, considerando-se os parasitas associados aos mesmos. Para validação do procedimento de projeto, concebeu-se e simulou-se através do programa ADS da Agilent um oscilador intitulado DVCO 3 GHz, cuja faixa de freqüência especificada estende-se de 1 a 3 GHz e a potência mínima de saída especificada é de 10 dBm. Um protótipo foi construído em circuito híbrido e seus resultados experimentais foram comparados aos simulados. A freqüência de oscilação medida foi de 1,04 GHz a 3,05 GHz e a potência obtida esteve entre 9,8 e 14,3 dBm, apresentando boa concordância com as simulações. O ruído de fase foi medido entre 100 kHz e 1 MHz de distância da portadora, observando-se uma inclinação proporcional a 1/f3. Verificou-se que a diminuição da corrente de polarização Ids dos transistores, através da redução de sua tensão de polarização de porta-fonte Vgs, melhorou o ruído de fase. Na condição de polarização de menor ruído de fase, observaram-se valores entre -84 e -93 dBc/Hz a 100 kHz da portadora. / In this dissertation, a design methodology applied to microwave reverse feedback distributed voltage controlled oscillators - DVCO - is proposed. This circuit constitutes a new class of oscillators, obtained from reverse feeding back of the distributed amplifier. The main advantage of this topology is its capacity to achieve ultra-wideband frequency tuning. Circuit theoretical background is presented and an extension of the linear analysis presented in the literature is proposed. It allows predicting transistor minimum transconductances and the oscillation initial frequency, considering m-derived artificial transmission lines. The proposed design method is applicable to reverse feedback DVCOs employing field effect transistors MESFET (Metal Semiconductor Field Effect Transistor) and PHEMT (Pseudomorfic High Electron Mobility Transistor), as well as using MIC (Microwave Integrated Circuits) and MMIC (Monolithic Microwave Integrated Circuits) technology. The proposed methodology defined criterion to employ real components, considering the component parasitics. In order to validate the design method, an oscillator named DVCO 3 GHz was designed and simulated through software Agilent ADS, with specified band from 1 up to 3 GHz and minimum output power of 10 dBm. A prototype was implemented in hybrid circuit technology and the measurements were compared to the simulation results. The measured oscillation frequency varied from 1,04 GHz up to 3,05 GHz and the output power was 9,8 to 14,3 dBm, presenting good agreement with simulations. Phase noise was measured in the range between 100 kHz and 1 MHz shift from carrier; in which it was observed a 1/f3 slope. It was verified that decreasing the transistor bias current Ids through decreasing its gate bias voltage Vgs reduced phase noise. In the biasing condition for lowest phase noise, values between -84 and -93 dBc/Hz at 100 kHz off-set from carrier were measured.

The design of 3D microwave devices can be improved by using computational optimization techniques combined with numerical simulations of the electromagnetic field. However, high accuracy field analysis is often computationally expensive and time consuming. One way to cut costs is to vary the accuracy level of the analysis at different stages of the optimization. This idea is based on the premise that the accuracy need not be constant throughout the optimization, and so the numerical analysis can be run more cheaply without compromising design quality. / This thesis presents a software system that minimizes the return loss of 3D microwave devices over a frequency band efficiently through accuracy control. It combines a custom gradient-based optimizer with a p-adaptive frequency-domain finite element solver. The solver computes the cost function and its gradient to a specified accuracy in a cost efficient manner. The p-adaptive solver comprises of two original components: an a-posteriori error estimator to evaluate the error in the cost function gradient, and an error indicator to identify the high error regions in the mesh. The optimizer controls the accuracy of the cost function evaluation through a link with the solver, specifying the required relative error for the gradient at each optimization step. / The combined adaption-optimization scheme was applied to 3D rectangular waveguide problems for validation: an E-plane miter bend, a U-bend, an impedance transformer and a compensated magic-T. For comparison, all the problems were also optimized using high-order finite elements at every step. Test results prove the computational efficiency of the new combined scheme at various stages of the optimization. In the early stages, when the element orders are low, the scheme is able to attain similar cost function reductions as the high-order analysis, with computational savings up to a factor of 25. Even in the late stages, when the accuracy is more stringent, the scheme manages a reduction in cumulative computation time of at least a factor of 4.

Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 79-86). Also available in electronic format on the Internet.