Ultra Low Power IEEE 802.15.4/ZIGBEE Compliant Transceiver

Low power wireless communications is the most demanding request among all wireless users. A battery life that can survive for years without being replaced, makes it realistic to implement many applications where the battery is unreachable (e.g. concrete walls) or expensive to change (e.g underground applications). IEEE 802.15.4/ZIGBEE standard is published to cover low power low cost applications, where the battery life can last for years, because of the 1% duty cycle of operation. A fully integrated 2.4GHz IEEE802.15.4 Compliant transceiver suitable for low power, low cost ZIGBEE applications is implemented. Direct conversion architecture is used in both Receiver and Transmitter, to achieve the minimum possible power and area. The chip is fabricated in a standard 0.18um CMOS technology. In the transmit mode, the transmitter chain (Modulator to PA) consumes 25mW, while in the receive mode, the iv receiver chain (LNA to Demodulator) consumes 5mW. The Integer-N Frequency Synthesizer consumes 8.5mW. Other Low power circuits are reported; A 13.56 Passive RFID tag and a low power ADC suitable for Built-In-Testing applications

A Novel Long-Range Passive UHF RFID System over Twisted-pair Cable

Radio Frequency Identification (RFID) is one of the most representative, rapidly growing, and highly extendable technologies, which uses electromagnetic waves in accordance with specific communications standards and regulations to identify, track, or even localise desired objects. However, due to its high cost, limited read range, and uncertain reliability, its adoption still lags, especially in large-scale organisations. Even though an RFID distributed antenna system (DAS) can greatly improve the detection range and read rate of a single reader when system uses different combinations of antenna states with frequency and phase hopping, the lossy and heavy coaxial cables between reader and antennas still limits the system coverage and design flexibility for wide-area passive UHF RFID applications. In order to develop a cost-efficient and flexibly-installed passive RFID DAS, a novel large-range passive UHF RFID system over twisted-pair cable is proposed in this dissertation. This new system consists of one baseband central controller and one antenna subsystem, connected by a commonly used twisted-pair cable. It is shown that transmitting/receiving low frequency baseband signals over a twisted-pair cable can significantly reduce cable attenuation and extend the communication distance. A simulation is conducted to demonstrate that frequency and phase hopping can also be remotely controlled to fit this system structure by slightly varying the frequency or phase of the input reference signal of the frequency synthesis system. The features of twisted-pair cable in terms of its low cost, light weight, and bend radius greatly improve the design and installation flexibility of an RFID system. The implemented system is designed based on the ISO 18000-6C and EPC Class 1 Generation 2 standards, and can operate according to FCC (902-928 MHz) and ETSI (865-868MHz) regulations. The results of the measurement show the reader can achieve a sensitivity of - 94.5 dBm over 30 m Cat5e cable, and its sensitivity can still remain at around -94.2 dBm over 150 m Cat5e cable. The experimental results of tag detection show that the passive tags can be successfully detected over a 6 m wireless range following a 300 m of twisted-pair cable between the central controller and antenna. This detection range cannot be achieved by existing commercial RFID systems. Since the transmission and reception in a RFID system are simultaneous, finite isolation of the circulator/directional coupler and environmentally dependent reflection ratio of the antenna lead to serious leakage problems. Leakage can directly cause sensitivity degradation due to saturation of the RF components. A fast leakage suppression block is developed in efforts to solve this problem. Measurements show that this new canceller can deliver an average suppression of 36.9 dB, and this excellent performance remains when the system uses frequency hopping. With help of an improved scanning algorithm, this canceller can find its optimal status within 38 ms, and this settling time is short enough for most commercial RFID readers. By reducing the number of voltage samples taken, the convergence time can be further improved. To fully investigate this new passive UHF RFID system value, a comparison study between the new system and a commercial system is conducted. This new automatic passive UHF RFID system is confirmed to deliver high performance long-range passive tag detection. Particular advantages are shown in the fast tag read rate and capability of uplink SNR improvement. This novel system is also superior to conventional RFID systems in terms of link distance, link cost, and installation flexibility

Design And Implementation Of A Low-cost, Compact And Long Range Monostatic Uhf Rfid Reader With Read Point Extension

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2014Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014RFiD sistemlerinin çeşitli uygulama alanlarında artan popülerliği neticesinde, özelikle UHF bandında çalışacak olan RFiD okuyucu üretimine dair ihtiyaçlar gittikçe artan bir eğilim göstermektedir. Bahsedilen ihtiyaçlar göz önüne alınarak, bu tez kapsamında yeni bir okuyucu tasarımı gerçekleştirilmiştir. Tasarlanan okuyucu, endüstriyel RFiD uygulamaları için gerekli görülen birçok ilgi çekici özelliği bünyesinde barındırmaktadır. RFiD sistemleri, kısaca radyo frekanslı kimliklendirme diye tanımlanabilmektedir. Elektromanyetik dalgaları kullanarak (kablosuz iletişim), üzerlerine RFiD etiketleri iliştirilmiş olan nesne, hayvan ve insanlardan verilerin transfer edilmesini sağlarlar. Takip, gözlem, kontrol vb. amaçlı kullanılabilmektedir. Genel itibari ile barkod sistemi gibi otomatik tanımlama teknolojileri ailesinin bir üyesidir. Tez kapsamındaki ilk iki bölümde, RFiD sisteminin detaylarına ve temel standartlarına dair bilgilere yer verilmiştir. Üçüncü bölümde, donanım sistem tasarımına ait süreçler detaylı bir şekilde ele alınmış ve simülasyon ile ölçüm sonuçlarına yer verilmiştir. Tasarlanan okuyucu; okuma noktası artırılmış, düşük maliyetli, kompakt, uzun menzilli ve Gen2 uyumlu olacak şekilde UHF bandında geliştirilmiştir. Aynı zamanda, birden fazla okuyucunun aynı anda çalıştığı yoğun ortamlarda çalışabilme özelliğine sahiptir. Okuyucu, anten çıkış gücü 30-dBm olan iki adet anten çıkış portu barındırmaktadır. Ayrıca, yenilikçi bir özellik olarak, geri yansıyan RF gücünü azaltmak için anten uydurma devresi tasarlanmıştır. Bu işlem, okuyucunun çıkış empedansının antenin empedansına uydurulması ile gerçekleştirilmektedir. Bununla birlikte, okuyucu, işlem anında antenin empedansını olası çevresel faktörlere karşı kararlı bir yapıda tutabilme kabiliyetine de sahiptir. Bunların yanı sıra, bir güç algılayıcı devresi vasıtasıyla, okuyucu için var olan yasal koşulları sağlamak adına, çıkış gücünü sınırlandırma ve kontrol etme özellikleri de mevcuttur. Donanım tasarımı esnasında, yüksek frekansta PCB tasarım teknikleri, radyo frekansı ve fizik temelleri, dijital ve analog devre tasarım teknikleri gibi farklı disiplinlerden çeşitli teknik bilgiler ve kabiliyetler kullanılmıştır. Artırılmış okuma noktası özelliği, tasarlanan bir başka donanım, RF çoklayıcı devresi, vasıtası ile sağlanmaktadır. Bu ürün sayesinde, UHF RFiD okuyucunun anten çıkışları artırılarak sistem kurulum maliyeti azaltılmaktadır. Bu cihazın amacı, çoklu anten ihtiyacı olan uygulamalarda okuyucu sayısını sabit tutarak, anten çıkış sayısını artırmaktır. Bu sayede sistemin uygulanma maliyetinde avantaj sağlanmaktadır. Ürün dahilindeki anahtarlama entegrelerinin araya girme kayıplarının az olması ve entegrelerin kontrolünü sağlayan denetleyici yapısı, okuyucuların marka modelinden bağımsız tak-çalıştır sistem modeli ürüne ait katma değerli nitelikleridir. Bu tez dahilinde tasarımı gerçekleştirilen UHF RFiD okuyucu, aynı zamanda Bilim, Sanayi ve Teknoloji Bakanlığı’nın sağlamış olduğu Ar-Ge proje destekleri kapsamında desteklenmiştir. Bu proje ve tez neticesinde, imalat masraflarını düşürmek adına okuyucu tasarımı ve üretimi yerli olarak gerçekleştirilmiş ve yurt içinde milli bir cihaz geliştirilmiştir. Proje sonucunda, başlangıçta belirlenen tüm kıstaslar başarıyla sağlanmış ve birer adet RF çoklayıcı devresi ve UHF RFiD okuyucu devresi, kontrol ünitesi ve grafiksel arayüz yazılımı ile birlikte, istenen herhangi bir RFiD uygulamasında kullanılmak üzere prototip olarak üretilmiştir.RFiD systems have an increasing popularity in various kinds of applications. Necessities are rising for the manufacture of new RFiD readers in industry especially at UHF band. Based on this concept, a new UHF RFiD reader design with extended read point capability has been presented within the scope of this thesis. Designed reader has attractive features required by some industrial RFiD applications. Before the hardware design part of the study, first, the background of RFiD and its key standards have been introduced in the first two chapters. In the third chapter, the hardware design process has been covered in detail and simulation and measurement results have been presented. The designed hardware is a low-cost, compact and long-range Gen2 compliant UHF RFiD reader with extended read point capability. The reader has up to 30 dBm (1 Watt) output RF power at two selectable antenna ports. The reader has an antenna tuning circuit, a novel feature, to reduce reflected RF power from antennas. This is achieved by tuning output impedance of the reader to the impedance of antenna. The reader can also tune the antenna impedance during operation in case the environment of the antenna changes. A power detector is used to control and limit the output power to regulatory requirements. While designing the hardware, several technical skills within a wide spectrum of disciplines were used like PCB design in high frequency, radio frequency, physics of RF, digital and analog design. Extended read point capability is provided with another hardware design called RF multiplexer circuit. This product has been designed in order to increase the number of antenna output ports of UHF RFiD reader to reduce the system implementation cost in dense antenna applications. This hardware design is also a part of another Research & Development project funded by the Ministry of Science, Industry and Technology of Turkey. As a part of this project and this thesis, the UHF RFiD reader has been designed as a domestic product to lower the cost of manufacture. As a result of this project, all the objectives have been achieved and a prototype of UHF RFiD reader, which has a control unit and a graphical user interface, and an RF multiplexer have been manufactured to be used in any desired UHF RFiD application.Yüksek LisansM.Sc

HIGH LINEARITY UNIVERSAL LNA DESIGNS FOR NEXT GENERATION WIRELESS APPLICATIONS

Design of the next generation (4G) systems is one of the most active and important area of research and development in wireless communications. The 2G and 3G technologies will still co-exist with the 4G for a certain period of time. Other applications such as wireless LAN (Local Area Network) and RFID are also widely used. As a result, there emerges a trend towards integrating multiple wireless functionalities into a single mobile device. Low noise amplifier (LNA), the most critical component of the receiver front-end, determines the sensitivity and noise figure of the receiver and is indispensable for the complete system. To satisfy the need for higher performance and diversity of wireless communication systems, three LNAs with different structures and techniques are proposed in the thesis based on the 4G applications. The first LNA is designed and optimized specifically for LTE applications, which could be easily added to the existing system to support different standards. In this cascode LNA, the nonlinearity coming from the common source (CS) and common gate (CG) stages are analyzed in detail, and a novel linear structure is proposed to enhance the linearity in a relatively wide bandwidth. The LNA has a bandwidth of 900MHz with the linearity of greater than 7.5dBm at the central frequency of 1.2GHz. Testing results show that the proposed structure effectively increases and maintains linearity of the LNA in a wide bandwidth. However, a broadband LNA that covers multiple frequency ranges appears more attractive due to system simplicity and low cost. The second design, a wideband LNA, is proposed to cover multiple wireless standards, such as LTE, RFID, GSM, and CDMA. A novel input-matching network is proposed to relax the tradeoff among noise figure and bandwidth. A high gain (>10dB) in a wide frequency range (1-3GHz) and a minimum NF of 2.5dB are achieved. The LNA consumes only 7mW on a 1.2V supply. The first and second LNAs are designed mainly for the LTE standard because it is the most widely used standard in the 4G communication systems. However, WiMAX, another 4G standard, is also being widely used in many applications. The third design targets on covering both the LTE and the WiMAX. An improved noise cancelling technique with gain enhancing structure is proposed in this design and the bandwidth is enlarged to 8GHz. In this frequency range, a maximum power gain of 14.5dB and a NF of 2.6-4.3dB are achieved. The core area of this LNA is 0.46x0.67mm2 and it consumes 17mW from a 1.2V supply. The three designs in the thesis work are proposed for the multi-standard applications based on the realization of the 4G technologies. The performance tradeoff among noise, linearity, and broadband impedance matching are explored and three new techniques are proposed for the tradeoff relaxation. The measurement results indicate the techniques effectively extend the bandwidth and suppress the increase of the NF and nonlinearity at high frequencies. The three proposed structures can be easily applied to the wideband and multi-standard LNA design

Analysis and design of UHF and millimetre wave radio frequency identification

Radio frequency identification (RFID) is an asymmetric radio protocol, where uplink communication (from transponder to reader) is implemented with backscattering modulation. The idea was first demonstrated in the 1940's. One of the first consumer applications of RFID was access control, and key cards based on an inductive near field coupling are widely used even today. The introduction of Schottky diodes to CMOS processes enabled passive RFID, i.e. transponders without a battery, at ultra high frequencies (UHF) with reasonable cost and read range in the end of 1990's. This has opened up new applications and inspired new research on RFID. This thesis studies the radio frequency (RF) components and general RF phenomena in RFID at UHF and millimetre waves. The theoretical analysis of the radio path reveals that the read range of a passive UHF system is ideally limited by the downlink, i.e. the power transfer from reader to the transponder. However, the architecture of the reader RF front end is critical, because the transmitted signal may couple a significant amount of noise to the receiver, overpowering the faint reflection from the transponder. In the thesis, two adaptive RF front ends are introduced to eliminate the noise coupling from the transmitter. One of the most critical problems with UHF RFID has been the detuning of transponder antennas on different mounting platforms. The detuning may significantly diminish the read range of the transponder, especially on metal surfaces. In this thesis, two backscattering-based measurement techniques for the transponder antennas are presented. The detuning effect has been studied using these measurement techniques, and a platform tolerant antenna is introduced. RFID at millimetre waves enables miniaturisation of the reader antenna, and widening the data bandwidth over short distances. This could be used to access wirelessly mass memories with wide data bandwidth. A semi-passive or active transponder could communicate, e.g., with automotive radars. The millimetre wave identification (MMID) has been theoretically studied and experimentally verified at 60 GHz

A Passive Harmonic Tag for Humidity Sensing

This paper describes a passive harmonic tag for radio frequency identification (RFID) and wireless sensor applications. The tag uses a dual polarized UHF patch antenna as an input antenna. One of the outputs is connected to a frequency doubler, which consists of a Schottky diode with its output connected to a patch tuned at twice the input frequency. The other output of the input antenna feeds a DC power harvested converter that drives an oscillator which modulates its output signal by controlling the bias point of the Schottky diode. The antenna’s output is also used as a humidity sensor. To achieve this, the antenna is loaded with an interdigital capacitor with humidity-dependent capacitance. The antenna is consequently detuned when humidity varies, and therefore the second harmonic power is received. The tag is manufactured using standard fiberglass substrate. The basic theory of harmonic tag operation is described and compared with the standard backscattering approach. Experimental results with a proof of concept using commercial components are presented

Passive und aktive Radio Frequency Identification Tags im 60-GHz-Band

Die Einführung des millimeter-Wellen-Bandes eröffnet neue Perspektiven für die Radio Frequency Identification (RFID) Kommunikationssysteme. Der Enwurf des Systems im 60-GHz-Band ermöglicht die Implementierung der On-Chip Antenne und darüber hinaus die Implementierung eines RFID-Tags auf einem einzigen Chip. Dennoch ist es aufgrund der gesetzlichen Beschränkung der effektiven isotropen Strahlungsleistung (EIRP) des Lesegeräts und der erhöhten Freiraum-Dielektrikumsverluste eine Herausforderung, eine zuverlässige Kommunikationsreichweite von mehreren Millimetern zu erreichen. Neue Lösungen sind für jeden Block sowohl im Lesegerät als auch im Single-Chip-Tag erforderlich. Obwohl das Lesegerät batteriebetrieben ist, ist es immer noch eine Herausforderung, die maximal zulässigen 20 dBm IERP des Lesersenders energieeffizient zu erzeugen. Darüber hinaus sollte der Empfänger einen ausreichenden Dynamikbereich haben, um das vom Tag kommende Signal zu erkennen. Auf der Tag-Seite sind die Hauptherausforderungen das Co-Design der effizienten On-Chip-Antennen-Implementierung, die hochempfindliche Gleichrichter-Implementierung und das Rückkommunikationskonzept. Diese Arbeit konzentriert sich auf die Machbarkeitsstudie des Single-Chip-RFID-Tags und die Implementierung im Millimeterwellenbereich. Es werden zwei Rückkommunikationskonzepte untersucht - Backscattering-Rückkommunikation und eine Kommunikation unter Verwendung von Ultra-Low-Power (ULP) Radios. Beide werden in einem 22 nm FDSOI Prozess auf einem Substrat mit geringem Widerstand implementiert. Beide Tags arbeiten mit einer Versorgungsspannung von 0,4 V, um die Kommunikationsreichweite zu maximieren. Die Link-Budgets sind so ausgelegt, dass sie die regulatorischen Beschränkungen einhalten. Die Auswahl des Technologieknotens wird begründet. Verschiedene Aspekte im Zusammenhang mit der Technologie werden diskutiert, wie z. B. Geräteleistung, passiver Qualitätsfaktor, Leistungsdichte der Kondensatoren. Der Backscattering RFID-Tag wird zuerst entworfen, da er eine relativ einfachere Topologie hat. Die Probleme der Gleichrichterempfindlichkeit im Rahmen des analogen Frontends, der On-Chip-Antenneneffizienz und der konjugierten Anpassung beider werden untersucht. Eine Kommunikationsreichweite von 5 mm wird angestrebt und realisiert. Um die Kommunikationsreichweite weiter zu erhöhen, wird in der zweiten Phase ein Tag mit einer aktiven Rückkommunikation implementiert. Hier wird die Gleichrichterempfindlichkeit weiter verbessert. Es wird ein 0,4V ULP Radio entworfen, das sich die Antenne mit dem Gleichrichter über einen Single-Pole- Double-Through (SPDT) Schalter teilt. Ein Abstand von 2 cm erwies sich als realisierbar, wobei die gesetzlichen Bestimmungen eingehalten und der dynamische Bereich des Leseempfängers nicht überschritten wurde. Es wird die höchste normalisierte Kommunikationsreichweite pro Leser-EIRP erreicht. Weitere Verbesserungsmöglichkeiten werden diskutiert

High-Isolation Low-Power Active Quasi-Circulator for 44GHz Transceiver with Power and Noise Optimization in 0.18 Micrometer BICMOS

Circulator is an important directional component in RF, microwave and millimeter wave communication front ends for certain communications, which requires transmitting and receiving signal simultaneously in the same band without switching of antenna from transmitter to receiver. As modern trend of wireless communication, conventional ferrite circulator is huge, bulky and heavy to be integrated with analog and digital baseband processing circuits. Active circulators provide a compact high isolation solution for low power application with smaller size and less cost with compatibility with modern IC. Previous works are majorly working at low frequency and paid little attention to power and noise requirement of active quasi-circulator working at the front end of a transceiver. A BiCMOS active quasi-circulator at 44GHz is designed in 0.18 μm process to provide high isolation low cost solution, which is comprised of in-phase divider and out-of-phase active combiner, with noise and power optimization. Moreover, techniques employed to improve isolation such as high Common mode rejection ratio(CMRR) balun design, common mode feedback, and novel method of power splitting and noise optimization, impedance matching scheme are discussed. High isolation of cascode structure is analyzed and major tradeoffs among characteristics are investigated, such as: gain and transmission-reception isolation; output impedance, matching and noise; linearity, power and efficiency. The circulator operates around 44 GHz with 3dB bandwidth of 4.53GHz, achieves maximum 2.897dBm input and 2.32dBm output power. Noise Figure (NF) is 10.62dB for reception path, only 0.03dB higher than NFmin. Linearity is reasonable for both in-phase divider and out-of-phase active combiner. OIP3 of in-phase divider is 8.15dBm, IIP3 is 4.48dBm, P1dB,in is -5.97dBm. OIP3 of out-of-phase active combiner is 5.18 dBm, IIP3 is 3.85dBm, P1dB, in is -2.79dBm. All the isolations better than -37 dB are achieved and forward gains better than 4 dB are achieved with power consumption 56.83mW. Large signal TX-RX isolation is 51.837dB. The circuit takes merely 1.415mm*1.014mm area. This active quasi-circulator offers a low cost substitute solution for circulator in low power applications

Sistemas eficientes de transmissão de energia sem-fios e identificação por radiofrequência

Doutoramento em Engenharia EletrotécnicaIn the IoT context, where billions of connected objects are expected to be ubiquitously deployed worldwide, the frequent battery maintenance of ubiquitous wireless nodes is undesirable or even impossible. In these scenarios, passive-backscatter radios will certainly play a crucial role due to their low cost, low complexity and battery-free operation. However, as passive-backscatter devices are chiefly limited by the WPT link, its efficiency optimization has been a major research concern over the years, gaining even more emphasis in the IoT context. Wireless power transfer has traditionally been carried out using CW signals, and the efficiency improvement has commonly been achieved through circuit design optimization. This thesis explores a fundamentally different approach, in which the optimization is focused on the powering waveforms, rather than the circuits. It is demonstrated through theoretical analysis, simulations and measurements that, given their greater ability to overcome the built-in voltage of rectifying devices, high PAPR multi-sine (MS) signals are capable of more efficiently exciting energy harvesting circuits when compared to CWs. By using optimal MS signals to excite rectifying devices, remarkable RF-DC conversion efficiency gains of up to 15 dB with respect to CW signals were obtained. In order to show the effectiveness of this approach to improve the communication range of passive-backscatter systems, a MS front-end was integrated in a commercial RFID reader and a significant range extension of 25% was observed. Furthermore, a software-defined radio RFID reader, compliant with ISO18000-6C standard and with MS capability, was constructed from scratch. By interrogating passive RFID transponders with MS waveforms, a transponder sensitivity improvement higher than 3 dB was obtained for optimal MS signals. Since the amplification and transmission of high PAPR signals is critical, this work also proposes efficient MS transmitting architectures based on space power combining techniques. This thesis also addresses other not less important issues, namely self-jamming in passive RFID readers, which is the second limiting factor of passive-backscatter systems. A suitable self-jamming suppression scheme was first used for CW signals and then extended to MS signals, yielding a CW isolation up to 50 dB and a MS isolation up 60 dB. Finally, a battery-less remote control system was developed and integrated in a commercial TV device with the purpose of demonstrating a practical application of wireless power transfer and passive-backscatter concepts. This allowed battery-free control of four basic functionalities of the TV (CH+,CH-,VOL+,VOL-).No contexto da internet das coisas (IoT), onde são esperados bilhões de objetos conectados espalhados pelo planeta de forma ubíqua, torna-se impraticável uma frequente manutenção e troca de baterias dos dispositivos sem fios ubíquos. Nestes cenários, os sistemas radio backscatter passivos terão um papel preponderante dado o seu baixo custo, baixa complexidade e não necessidade de baterias nos nós móveis. Uma vez que a transmissão de energia sem fios é o principal aspeto limitativo nestes sistemas, a sua otimização tem sido um tema central de investigação, ganhando ainda mais ênfase no contexto IoT. Tradicionalmente, a transferência de energia sem-fios é feita através de sinais CW e a maximização da eficiência é conseguida através da otimização dos circuitos recetores. Neste trabalho explora-se uma abordagem fundamentalmente diferente, em que a otimização foca-se nas formas de onda em vez dos circuitos. Demonstra-se, teoricamente e através de simulações e medidas que, devido à sua maior capacidade em superar a barreira de potencial intrínseca dos dispositivos retificadores, os sinais multi-seno (MS) de elevado PAPR são capazes de excitar os circuitos de colheita de energia de forma mais eficiente quando comparados com o sinal CW tradicional. Usando sinais MS ótimos em circuitos retificadores, foram verificadas experimentalmente melhorias de eficiência de conversão RF-DC notáveis de até 15 dB relativamente ao sinal CW. A fim de mostrar a eficácia desta abordagem na melhoria da distância de comunicação de sistemas backscatter passivos, integrou-se um front-end MS num leitor RFID comercial e observou-se um aumento significativo de 25% na distância de leitura. Além disso, desenvolveu-se de raiz um leitor RFID baseado em software rádio, compatível com o protocolo ISO18000-6C e capaz de gerar sinais MS, com os quais interrogou-se transponders passivos, obtendo-se ganhos de sensibilidade dos transponders maiores que 3 dB. Uma vez que a amplificação de sinais de elevado PAPR é uma operação crítica, propôs-se também novas arquiteturas eficientes de transmissão baseadas na combinação de sinais em espaço livre. Esta tese aborda também outros aspetos não menos importantes, como o self-jamming em leitores RFID passivos, tido como o segundo fator limitativo neste tipo de sistemas. Estudou-se técnicas de cancelamento de self-jamming CW e estendeu-se o conceito a sinais MS, tendo-se obtido isolamentos entre o transmissor e o recetor de até 50 dB no primeiro caso e de até 60 dB no segundo. Finalmente, com o objetivo de demonstrar uma aplicação prática dos conceitos de transmissão de energia sem fios e comunicação backscatter, desenvolveu-se um sistema de controlo remoto sem pilhas, cujo protótipo foi integrado num televisor comercial a fim de controlar quatro funcionalidades básicas (CH+,CH-,VOL+,VOL-)