Design of efficient microwave power amplifier systems

In the future communication systems, it is of key importance that the transceivers are capable of operating in multiple frequency bands and with complex signals. In this context, the power amplifier is a critical component of the transceiver, since it is responsible for most of the total power consumption in base stations and portable devices. Apart from the power consumption, the design of power amplifier systems must account for multi-band/broadband capabilities, high peak-toaverage power ratio signals and the mismatch effect caused by the various operating conditions. Hence, the design of power amplifier topologies that enhance the total system efficiency and reliability is a challenging task. This PhD dissertation introduces novel power amplifier architectures and solutions for modern communication systems. The contributions of this thesis can be divided in two parts. The first part deals with the study and design of power amplifier systems. It is of major importance that these designs provide linear amplification and operation at multiple frequency bands, which will permit the reduction of the cost and size of the devices. Additionally, we investigate the possibility to harvest the dissipated power from the power amplification process. For the development of the prototypes, lumped-element topologies, transmission line implementation and Substrate Integrated Waveguide (SIW) technology are adopted. In the second part of the thesis, novel matching networks are introduced and their properties are studied. In particular, resistance compression topologies are proposed to overcome the performance degradation associated with the sensitivity of nonlinear devices to environmental changes. These networks can be adopted in modern power amplifier architectures, such as envelope tracking and outphasing energy recovery power amplifier topologies, in order to provide improved performance over a wide range of operating conditions.Es primordial que los transceptores de los futuros sistemas de comunicación sean capaces de operar en múltiples bandas de frecuencia y con señales complejas. En este contexto, el amplificador de potencia es un componente crítico del transceptor dado que su consumo energético supone la mayor parte del consumo tanto de las estaciones base como de los dispositivos móviles. Aparte del consumo energético, los nuevos diseños de sistemas de amplificación de potencia deben considerar aspectos como la capacidad de operar en múltiples bandas o en banda ancha, el uso de señales con alta relación de potencia pico a potencia media (PAPR) y el efecto de desadaptación que aparece bajo las diferentes condiciones de funcionamiento. Por lo tanto, el diseño de nuevas topologías para amplificadores de potencia que mejoren la eficiencia total del sistema y la fiabilidad es una tarea compleja. Esta tesis doctoral presenta nuevas arquitecturas de amplificadores de potencia y soluciones para los sistemas de comunicación modernos. Las contribuciones de esta tesis se pueden dividir en dos partes. La primera parte se centra en el estudio y diseño de sistemas de amplificación de potencia con el fin de proporcionar amplificación lineal y funcionamiento en múltiples bandas de frecuencia, lo que permitirá reducir el coste y tamaño de los dispositivos. Además, se investiga la posibilidad de reutilizar la energía disipada en el proceso de amplificación de potencia. Para el desarrollo de los prototipos, se utilizan topologías hibridas, implementaciones con líneas de transmisión y tecnología de guía de onda integrada en sustrato (SIW). En la segunda parte de la tesis, se proponen redes de adaptación y se estudian sus propiedades. En particular, se proponen topologías de compresión de resistencia para minimizar el efecto que producen en el rendimiento la sensibilidad de los dispositivos no lineales a los cambios ambientales. Estas redes pueden ser utilizadas en arquitecturas modernas de amplificadores de potencia como pueden ser las topologías envelope tracking y outphasing energy recovery con el fin de proporcionar un rendimiento mejorado bajo múltiples condiciones de funcionamiento

Dual-Band Rectifier Based on Resistance Compression Networks

This work presents the design of a dual-band rectifier operating at 915 MHz and 2.45 GHz with minimized sensitivity to input power and load variations. The rectifier is designed using a dual-band resistance compression network (RCN) for minimizing the effect of input power and load changes and it is based on Composite Right/Left-Handed (CRLH) to implement the dual band operation. The resulting rectifier has shown good RF-DC conversion efficiency and reduced sensitivity to variations

Exploring the Boundaries of Ambient RF Energy Harvesting With LoRaWAN

—Environmental monitoring is an important application for wireless sensing devices. Battery power requires in-the-field replacement, and the chemicals involved are environmentally harmful, so harvested energy is a useful alternative. Previous research has shown the feasibility of powering LoRaWAN sensors using high-energy ambient or wireless transfer power sources. This article extends this work by exploring the boundaries of using low-energy radio-frequency (RF) ambient sources. Ambient RF energy harvesting is an attractive option, but it is more challenging due to the low levels of energy density typically available. Using an analytical LoRaWAN device model and RF energy data collected from around the world, a systematic investigation of the design and environmental space is performed. The main contribution of this article is to identify the boundaries of feasibility for powering LoRaWAN sensor nodes from ambient RF energy. These boundaries include design and environmental factors

Behavioural Models for Distributed Arrays of High Performance Doherty Power Amplifiers

Behavioral models are intended as high level mathematical descriptions which require less computational effort to simulate behavior compared to physical or circuit level equivalent models. When designed and dimensioned properly they are well suited to concise characterization of power amplifiers under different operating conditions. In this paper we compare the relative performance of several behavioral models for modelling an asymmetric Doherty power amplifier for their use in distributed arrays

Dual-Band Resistance Compression Networks for Improved Rectifier Performance

In this work, the concept of dual-band resistance compression networks is introduced and applied to the design of rectifier circuits with improved performance. The use of resistance compression networks (RCNs) minimizes the sensitivity of rectifier circuits to variations in the surrounding environment, such as input power level and changes in the rectifier load. The proposed dual-band RCN can be used as the matching network located between the antenna and the rectifying element of a dual-band rectifier for energy harvesting applications. A dual-band ( 915 MHz /2.45 GHz) rectifier based on RCN is designed and characterized showing improved performance in comparison with a conventional dual-band envelope detector by exhibiting improved RF-dc conversion efficiency and reduced sensitivity versus output load and input power variations

Rectenna Design and Signal Optimization for Electromagnetic Energy Harvesting and Wireless Power Transfer

This work addresses two key topics in the field of energy harvesting and wireless power transfer. The first is the optimum signal design for improved RF-DC conversion efficiency in rectifier circuits by using time varying envelope signals. The second is the design of rectifiers that present reduced sensitivity to input power and output load variations by introducing resistance compression network (RCN) structures