One of the key building blocks in a direct-conversion receiver is the low noise amplifier (LNA), which needs to provide a sufficient gain with a low noise figure for the RF front-end. However, the wideband nature of the receiver imposes harsh requirements on the LNA. It is difficult to achieve desired performance goals over the wide frequency range without excessive power consumption. To deal with this problem, this thesis proposes a novel band-selective UWB LNA. Utilizing the frequency hopping property of the MB-OFDM system, the proposed method switches the operating frequency of the LNA in real time following the MB-OFDM's hopping pattern so that optimal gain and noise performance can be achieved in each frequency band. Unlike the conventional approach, this LNA does not need to cover the entire band simultaneously, thus excessive power consumption is avoided. Fabricated in a 0.18-mum CMOS process, the proposed LNA achieves a peak power gain of 16 dB and a minimum noise figure of 2.74 dB at a low power consumption of less than 12 mW. / Other challenges in direct-conversion MB-OFDM receivers include ultra-short band switching time and wide LO frequency range. The single-sideband (SSB) generation is an attractive method for a fast-hopping multi-band LO generator. However, it involves LO frequency synthesis in an open-loop architecture, and thus the spurious-tone performance becomes critical in maintaining the LO signal integrity. Since the accuracy of the SSB generation and the spurious-tone power are difficult to control in a high-frequency operation, a 4.5-GHz SSB upconverter system was fabricated in a standard 0.18-mum CMOS process to investigate its performance against process variation. Some precise quadrature signal generation circuits such as divider and polyphase filter are employed. Experimental results show that the fabricated SSB upconverter system achieves image rejection of higher than 48 dB and spurious-tone suppression of higher than 32 dB. / The use of an active downconversion mixer is an alternative to relax the LNA requirements for direct-conversion MB-OFDM UWB receivers. However, its linearity becomes a problem when the bandwidth is ultra wide. In this thesis, the static current bleeding technique is used in the UWB downconversion mixer to improve its linearity. By injecting a DC current to the RF transconductor for linearization, the mixer's transconductance is enhanced while the noise from the LO switches is not affected. As a result, the conversion gain increases and the noise figure improves. Fabricated in a 0.18-mum CMOS process, the UWB downconversion mixer achieves a peak conversion gain of 4.1 dB, a peak IIP3 of --2.5 dBm, and a minimum double-sideband (DSB) noise figure of 11.7 dB at a low power consumption of 6 mW. / Ultra-wideband (UWB) is a short-range, high-data-rate communication system for Wireless Personal Area Networks (WPAN) based on the IEEE 802.15.3a physical layer standard. The allocated frequency range is from 3.1 to 10.6 GHz, in which 14 bands are defined. The first band group, which is assigned to the mandatory Mode 1 devices, consists of three bands. In UWB systems, multi-band orthogonal frequency division multiplexing (MB-OFDM) is the dominant modulation scheme for its high spectral flexibility and its similarity in communication architecture with other existing wireless communication standards, such as IEEE 802.11a/b/g and WiMAX. For practical reasons, the direct-conversion architecture is widely considered the best architecture to implement an MB-OFDM UWB receiver, which has advantages of low power consumption and high integration level. Nevertheless, there are some performance limitations in direct-conversion MB-OFDM UWB receivers. In this thesis, some key building blocks in the RF front-end of the direct-conversion MB-OFDM UWB receivers for use in Mode 1 devices are investigated to overcome such limitations. / Tang, Siu Kei. / "May 2008." / Adviser: Pun Kong Pang. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1857. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 161-169). / 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, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Cette thèse s’intéresse à la conception d’antennes ultra large bande reconfigurables. Cette étude a été motivée par le souhait de regrouper l’ensemble des antennes d’observation présentes sur les satellites en un panneau rayonnant unique afin de pouvoir réduire la taille de ces derniers. Les travaux présentés dans ce mémoire sont donc principalement axés sur la conception d’antennes spirales et sur les améliorations qui peuvent leur être apportées. Ainsi, une nouvelle topologie d’antenne spirale carrée reconfigurable en un réseau de quatre antennes spirales carrées plus petites sur la même ouverture rayonnante est exposée. Cette reconfiguration permet d’augmenter l’efficacité de surface de la structure tout en offrant de nouvelles possibilités d’utilisation à l’antenne et en améliorant ses performances. Les caractéristiques et les performances des deux configurations en états figés sont détaillées. Les maquettes réalisées et les résultats de mesure sont également présentés afin de valider le fonctionnement de l’antenne. Ensuite, différentes améliorations de cette structure sont présentées ainsi qu’une application possible. Enfin, une solution permettant d’améliorer le fonctionnement des antennes spirales imprimées au-dessus d’un plan de masse est décrite. En effet, cette solution permet de supprimer un nul de rayonnement lorsque l’antenne se situe à une demi-longueur d’onde du plan de masse. Sa bande passante d’utilisation peut ainsi être potentiellement doublée sans perdre la moitié de l’énergie comme avec l’utilisation d’absorbants. Cette technique consiste à ajouter un élément rayonnant parasite au-dessus de l’antenne. Cet élément est excité par couplage à l’antenne spirale et rayonne à la fréquence du nul de rayonnement. Cet élément étant faible bande, il ne dégrade pas le fonctionnement de l’antenne aux autres fréquences de la bande passante. Une structure utilisant ce concept a été réalisée afin de valider son fonctionnement. / This thesis focuses on the design of ultrawideband reconfigurable antennas. The objective of this study is to integrate all the antennas of observation on satellites into a single radiating panel and make it reconfigurable. Works presented in this document are focused on the design of spiral antennas and on their possible improvements. Thereby, a new topology of square spiral antenna reconfigurable into an array of four smaller square spiral antennas is shown. This reconfiguration allows increasing the surface efficiency of the structure while offering new possibilities of utilization to the antenna and improving its performance. Characteristics and performance of both configurations in frozen states are presented. Breadboards and measurements are also presented in order to validate the functioning of the antenna. Then, several improvements of this structure are studied and a possible application. Finally, a solution for improving the functioning of spiral antennas printed over a metallic ground plane is presented. This solution permits to remove a null of radiation when the distance between the antenna and the ground plane is a multiple of the half wavelength. In this way, its bandwidth can be doubled without losing the half of the energy like with absorbers. This technique consists in adding a parasitic radiating element over the antenna. This element is fed by coupling to the spiral antenna and radiates at the frequency of the null of radiation. This element is narrowband, so antenna performance remains unchanged at the other frequencies of the bandwidth. A structure using this concept has been made in order to validate its functioning.

A tecnologia de radar e comunicação em banda ultralarga (UWB) tem sido investigada intensamente nas últimas décadas. Esta tecnologia emprega pulsos de curta duração, que resultam em um espalhamento de energia em uma faixa ampla de frequência, fazendo com que, em transmissão de dados, o sinal apareça como ruído branco, dificultando a sua interceptação. Uma das aplicações mais promissoras da tecnologia UWB é na implementação de radares para detecção de pessoas, no monitoramento de ambientes, no uso em missões de resgate em desmoronamento de construções e na detecção de pessoas soterradas. Entretanto, diversos são os desafios para a construção de radares UWB: geração e recepção do pulso UWB, antenas, processamento, análise e visualização dos dados. Este trabalho propõe uma nova antena para aplicações de radar para visualização através da parede, e realiza a sua caracterização usando algoritmos de detecção de pessoas. Para a caracterização, o trabalho apresenta um cenário experimental que utiliza um sistema de caracterização de antena UWB. A antena proposta consiste em modificações na estrutura de uma antena antipodal, de forma a se obter alto ganho e estabilidade nos diagramas de irradiação, requisitos importantes para esse tipo de aplicação. Os resultados obtidos experimentalmente mostram que a antena proposta apresenta diagrama de irradiação direcional e principalmente alto ganho, característica importante para as aplicações de detecção. Processando-se os dados obtidos experimentalmente com algoritmos de detecção clássicos e adaptativo, verificou-se que a antena cumpre os requisitos da aplicação de detecção de pessoas. / Ultra-Wideband (UWB) radar and communication systems have been widely studied in the last decades. This technology employs very short duration pulses, resulting in energy spreaded in a very wide frequency band. In data communication applications, the signal appears as a white noise, making difficult the interception. One of the most promising applications of this technology is in radar implementation for people detection, in environment monitoring, rescue missions etc. The challenges to UWB radar implementation area diverse: pulse generation, pulse transmission and reception, antennas, and data processing, analysis and visualization. This work proposes a new antenna for through the wall (TTW) UWB radar. The antenna is characterized using people detection algorithms. A scenario, composed by a UWB antenna characterization system is presented. The antenna is a antipodal antenna modified in order to obtain high gain and stability in the irradiation diagram. Using people detection algorithms, it was verified full attendance to application requirements.

Distributed MIMO (DMIMO) communications and specifically the idea of distributed transmit beamforming involves multiple transmitters coordinating among themselves to form a virtual antenna array and steer a beam to one or more receivers. Recent works have successfully demonstrated this concept of beamforming with narrowband, frequency-flat wireless channels. We consider the generalization of this concept to wideband, frequency selective channels and propose two Figures of Merit (FOMs), namely, communication capacity and received power to measure the performance of beamforming. We formulate the precoder design that maximizes the two FOMs as optimization problems and derive general properties of the optimal precoders. The two metrics are equivalent with frequency-flat channels, whereas, they result in vastly different optimal criteria with wideband channels. The capacity maximizing solution also differs from classical water-filling due to the per-transmitter power constraints of the distributed beamforming setting, whereas, the power maximizing solution involves the array nodes concentrating their power in a small, finite set of frequencies resulting in an overall received signal consisting of a small number of sinusoidal tones. We have not been able to derive closed-form solutions for the optimal precoders, but we provide fixed point algorithms that efficiently computes these precoders numerically. We show using simulations that solution to both these maximization problems can yield substantially better performance as compared to simple alternatives such as equal power allocation. The fixed point algorithms also suggest a distributed implementation where each node can compute these precoders on their own iteratively using feedback from a cooperating receiver. We also establish the relationship between various precoders. The idea of maximizing received power suggests a natural application of wireless power transfer(WPT). However, the large-scale propagation losses associated with radiative fields makes antennas unattractive for WPT systems. Motivated by this observation, we also consider the problem of optimizing the efficiency of WPT to a receiver coil from multiple transmitters using near-field coupling. This idea of WPT using near-field coupling is not new; however, the difficulty of constructing tractable and realistic circuit models has limited the ability to accurately predicting and optimizing the performance of these systems. We present a new simple theoretical model and take the more abstract approach of modeling the WPT system as a linear circuit whose input-output relationship is expressed in terms of a small number of unknown parameters. We present a simple derivation of the optimal voltage excitations to be applied at the transmitters to maximize efficiency, and also some general properties of the optimal solution. Obviously, the optimal solution is a function of unknown parameters, and we describe a procedure to estimate these parameters using a set of direct measurements. We also present a series of experimental results, first, with two transmitter coils and a receiver coil in a variety of configurations and then with four transmitter coils and two receiver coils to illustrate our approach and the efficiency increase achieved by using the calculated optimal solution from our model.

This thesis studies the problem of estimating the interior structure of a collapsed building using embedded Ultra-Wideband (UWB) radios as sensors. The two major sensing problems needed to build the mapping system are determining wall type and wall orientation. We develop sensing algorithms that determine (1) load-bearing wall composition, thickness, and location and (2) wall position within the indoor cavity. We use extensive experimentation and measurement to develop those algorithms. In order to identify wall types and locations, our research approach uses Received Signal Strength (RSS) measurement between pairs of UWB radios. We create an extensive database of UWB signal propagation data through various wall types and thicknesses. Once the database is built, fingerprinting algorithms are developed which determine the best match between measurement data and database information. For wall mapping, we use measurement of Time of Arrival (ToA) and Angle of Arrival (AoA) between pairs of radios in the same cavity. Using this data and a novel algorithm, we demonstrate how to determine wall material type, thickness, location, and the topology of the wall. Our research methodology utilizes experimental measurements to create the database of signal propagation through different wall materials. The work also performs measurements to determine wall position in simulated scenarios. We ran the developed algorithms over the measurement data and characterized the error behavior of the solutions. The experimental test bed uses Time Domain UWB radios with a center frequency of 4.7 GHz and bandwidth of over 3.2 GHz. The software was provided by Time Domain as well, including Performance Analysis Tool, Ranging application, and AoA application. For wall type identification, we use the P200 radio. And for wall mapping, we built a special UWB radio with both angle and distance measurement capability using one P200 radio and one P210 radio. In our experimental design for wall identification, we varied wall type and distance between the radios, while fixing the number of radios, transmit power and the number of antennas per radio. For wall mapping, we varied the locations of reference node sensors and receiver sensors on adjoining and opposite walls, while fixing cavity size, transmit power, and the number of antennas per radio. As we present in following chapters, our algorithms have very small estimation errors and can precisely identify wall types and wall positions.

Ultra Wideband (UWB) is an emerging technology for use in the indoor wireless personal area networks and ad hoc networks. The more common form of UWB which uses sub-nanosecond pulses without any form of carrier signal is considered in this research. UWB signals have a large bandwidth with allocated frequency spectrum from 3.1 GHz to 10.6 GHz and maximum power restricted to -41dBm/MHz. The IEEE 802.11a is a popular standard for high data rate wireless local area networks (WLANs). The operating frequency of the IEEE 802.11a WLAN is 5 GHz which is right inside the allocated UWB frequency spectrum. One of the main obstacles facing the implementation of UWB devices is the challenge of reducing interference caused by UWB to other systems and vice versa. The potential operating areas/frequencies of the IEEE 802.11a WLAN and UWB systems overlap and therefore the problem of UWB interference to the IEEE 802.11a WLANs and vice versa becomes significant. In this research we have focused on studying the effect of UWB interference on IEEE 802.11a WLANs. The different UWB parameters that affect the interference caused by UWB to IEEE 802.11a WLAN have been considered for determining their effect on the performance of the IEEE 802.11a WLAN. The effect of UWB multipath on the performance of the IEEE 802.11a WLAN has been observed. The UWB parameters have also been compared based on their effect on the performance of the IEEE 802.11a system in the presence of UWB multipath. Additionally, two different interference mitigation techniques that reduce UWB interference to the IEEE 802.11a WLANs have been studied.

This work details the design and fabrication of an ultra-wideband periodic spiral antenna (PSA) with a notch filter embedded directly into the radiating aperture. Prototype fabrication of the PSA reveals long assembly time due to forming the antenna element, therefore modifications are made to allow fabricating the antenna elements on a thin, flexible, Polyimide substrate. A transmission line model is develop to support the updated configuration of the antenna elements. In addition, a symmetric spurline filter is integrated into the arms of the spiral antenna in order to address the common problem of interference in ultra-wideband systems. For the first time, a placement study is conducted to show the optimal location of the filter as a function of frequency. The presented transmission line model demonstrates the ability to decouple the design of the filter and antenna by being able to predict the resonant frequency and achieved rejection after integration of the two. Measured results show a gain rejection of 21 dB along with the ability to tune the resonance of the filter from 1.1 – 2.7 GHz using a lumped capacitor. For high power applications, thermal measurements are conducted, and for the first time, thermal profiles along the top of the antenna are used to show the radiation bands in a spiral antenna. Power tests are successfully conducted up to 40 W across the entire operational bandwidth and up to 60 W for 2 GHz and below. At these elevated power levels, a large voltage is generated across the lumped capacitor used to tune the resonance of the spurline filter; this issue is addressed through the development of a capacitive wedge that is overlapped on top of the spurline stub, which increases the voltage handling to 2,756 V. Measured results reveal a reduced tuning range compared to using lumped capacitors and a gain rejection of greater than 10 dB for all configurations.

[pt] O correto planejamento de novas redes de comunicação sem fio de voz e dados representa um grande desafio ao incluir serviços cada vez mais avançados com diferentes requisitos de qualidade, suporte a mobilidade, altas taxas de transmissão e capacidades de tráfego elevadas. Os ambientes nos quais estas redes operam são dos mais diversos e contemplam desde na áreas abertas até centros urbanos com alta densidade de edificações. O presente trabalho apresenta resultados experimentais que permitem caracterizar o canal de radio-propagação num ambiente urbano com mobilidade do receptor. Como resultado de campanhas de medições, são identificados modelos do canal que permitem ao projetista da rede definir a melhor configuração de parâmetros e critérios de projeto para a implantação de uma rede móvel de acesso sem fio em banda larga. As medições foram realizadas nos bairros da Gávea, Leblon e Lagoa, no Rio de Janeiro, com estação transmissora instalada na PUC-Rio (prédio LEME) na frequência de 3,5 GHz, destinada para novos serviços móveis. Os principais resultados obtidos são: o desenvolvimento de uma metodologia de medição simples e precisa, utilizando a técnica OFDM, e das ferramentas de software para pré-processamento e analise de dados; o desenvolvimento de modelos semi-empíricos para a previsão da perda média de propagação; a obtenção de perfis de retardo do canal e dos valores médio e desvio padrão do retardo em condições de visibilidade (LOS) e obstrução (NLOS), e de expressões empíricas para sua estimativa; a obtenção do valor médio das amplitudes relativas dos multipercursos e sua modelagem em função do valor de retardo relativo. / [en] Best practices of radio planning for new wireless networks with mixed trac of voice and data are a big technical challenge due to the need to provide of advanced services with different quality requirements, high data throughput, mobility and high traffic demands. Environments for operation of this kind of networks are diverse and include open areas with low population density as well as urban centers. This thesis presents experimental results obtained to characterize the wideband radiopropagation channel on urban environments with a mobile receiver. The analysis of measured data allows the identification of channel models and propagation mechanisms needed for the design engineer to define the best parameter configuration and project criteria in the deployment of a wideband mobile wireless network. The measurement campaign was executed on Gavea neigborhood in Rio de Janeiro city with a transmitter station located in a PUC-Rio university building (Lcme Building) operating at 3,5 GHz, frequency used for the new wideband mobile services. The main results are: the development of a simple and precise methodology for measuring, using the OFDM technique OFDM, and the software tools for pre-processing and analysis; the development of semi-empirical models for predicting the average propagation loss in the urban environment; measurements of multipath delay profiles of the channel and the average values and standard deviation of the RMS delay spread in visibility (LOS) and obstruction (NLOS) conditions, and derivation of empirical expressions for their estimation; measurements of the average values of multipath amplitudes its modeling in function of the relative delay.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

<p>Ultra Wideband Radio (UWB) is an upcoming alternative for wireless communications. Since the Federal Communication Commission in the USA allowed UWB for unlicensed usage in April 2002, more and more companies have started developing UWB systems. </p><p>The major difference with UWB compared to other RF systems is that UWB sends information with pulses instead of using a carrier wave. The technique is from the nineteenth century and was first developed by Heinrich Hertz (1857-1894), which led to transatlantic communications 1901. </p><p>This Master thesis presents a proposal of a transmitter for Ultra Wideband Radio using multiple bands. The proposed transmitter is implemented on system level in Simulink, Matlab. The frequency generation in the transmitter is also implemented at component level in a 0.13 um IBM process. The thesis begins with an introduction of UWB theory and techniques.</p>