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The conventional Doherty architecture is commonly used in wireless transmitters for its ability to boost the average efficiency of a traditional single-ended class B amplifier. It consists of two parallel single-ended amplifying branches (named carrier and peaking amplifiers) which are linked, at the output, through a /4 combiner. This output combiner commonly has a significant impact on the overall bandwidth, as it is usually built from a transmission line structure with tuned dimensions. Other non-conventional combining structures could be designed, targeting a wider bandwidth, contributing to an overall increase of the Doherty amplifier’s bandwidth. Being this an high relevance research topic for the development of high efficient and broadband amplifiers, it is highly desirable to have a laboratory setup that implements a Doherty power amplifier to which distinct output combiner structures can be connected and tested. In that sense, the design of two single-ended amplifiers (the carrier and the peaking) was performed in a circuit simulator (ADS, from Keysight) together with the input power divider that compose the Doherty architecture. The Doherty amplifier main board was designed to incorporate the carrier and peaking amplifiers, and also the power splitter at the input, and it was prepared so that it could be connected to any desired combiner to be tested. A traditional Doherty power combiner was designed and both boards (Doherty amplifier and the combiner) were produced, connected and tested in the RF laboratory. The measured amplifier presented the typical caractheristics of a Doherty amplifier with nearly 75% of drain efficiency at full-power, and nearly 50% at the output back-off level. In addition, a second combiner unit was designed with two purposes. The first was to demonstrate the operation of the designed Doherty amplifier with a distinct output combiner, showing that, as intended in this work, it is suited to test multiple combiner structures. The second objective was to serve as preliminary test to evaluate the possibility of merging the output combiner with the antenna element. Taking advantage of the electromagnetic coupling between antennas, this second combiner structure uses two antenna elements that were tuned to simultaneously behave as output combiner of the Doherty amplifier and a radiating element. A arquitetura Doherty convencional é tipicamente utilizada em transmissores sem fios pela sua capacidade de aumentar a eficiência média de um tradicional amplificador em classe B. O amplificador Doherty consiste em dois amplificadores em paralelo (chamados de amplificadores carrier e peaking) que são ligados, na saída, através de um combinador de /4. Este combinador de saída geralmente tem um impacto significativo na largura de banda do amplificador, pois é tipicamente construído a partir de uma estrutura de linhas de transmissão com dimensões ajustadas para uma frequência. Outras estruturas de combinadores não convencionais podem ser projetadas, visando uma largura de banda maior, contribuindo para um aumento geral da largura de banda do amplificador Doherty. Sendo este um tópico de investigação de elevada relevância para o desenvolvimento de amplificadores de alta eficiência e largura de banda, seria interessante ter um setup de laboratório que implemente um amplificador de potência Doherty para o qual estruturas combinadoras distintas possam ser ligadas à saída do amplificador e testadas. Nesse sentido, o projeto de dois amplificadores (carrier e peaking) foi realizado num simulador de circuitos (ADS, da Keysight) junto com o divisor de potência de entrada que compõe a arquitetura Doherty. A placa principal do amplificador Doherty foi projetada para incorporar os amplificadores carrier e peaking, e também o divisor de potência na entrada, e foi preparada de modo que pudesse ser ligada a qualquer combinador desejado a ser testado. Um combinador de potência Doherty tradicional foi projetado e ambas as placas (amplificador Doherty e o combinador) foram produzidas, soldadas e testadas no laboratório de RF. O amplificador medido apresentou as características típicas de um amplificador Doherty com aproximadamente 75% de eficiência de dreno na potência máxima e aproximadamente 50% no ponto de output back-off. Além disso, foi projetado um segundo combinador com dois objetivos. O primeiro foi demonstrar o funcionamento do amplificador Doherty projetado com um combinador de saída distinto, mostrando que, como pretendido neste trabalho, o amplificador desenhado é adequado para testar múltiplas estruturas combinadoras. O segundo objetivo foi servir como teste preliminar para avaliar a possibilidade de fundir o combinador de saída com a antena. Aproveitando o acoplamento eletromagnético entre antenas, esta segunda estrutura combinadora utiliza duas antenas que foram projetadas para se comportarem simultaneamente como combinador de saída do amplificador Doherty e como elemento radiante. Mestrado em Engenharia Eletrónica e Telecomunicações

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Tunable matching networks are essential components for agile radio frequency systems. To optimally design such networks, the total area they cover on the Smith chart needs to be determined. In this work, the coverage areas of typical matching networks have been determined analytically for the first time. It has been found that the coverage area is encompassed by up to five arcs. Analytical expressions for the centers and radii for these arcs have been derived. The theoretical analysis is provided for four typical matching networks and verified by circuit simulation and measured data. Moreover, a dynamically load-modulated power amplifier has been designed using the presented theoretical techniques, which demonstrates a measured improvement in the power added efficiency of up to 5\% in the frequency range of (0.8 - 0.9) GHz.

This paper presents a novel adaptive power amplifier (PA) architecture for performing dynamic-load-modulation. For the first time, a dynamically-load-modulated PA design that achieves octave bandwidth, high power and high efficiency simultaneously is experimentally demonstrated. This PA design is based on a commercial GaN HEMT. The output matching scheme incorporates a broadband static matching for high-efficiency at the maximum power level and a wideband dynamic matching for efficiency enhancement at power back-offs. The impedance and frequency tunability is realized using silicon diode varactors with a very high breakdown voltage of 90 V. Experimental results show that a dynamic-load-modulation from maximum power to 10-dB back-off is achieved from 1 to 1.9 GHz, with a measured performance of approximate to 10-W peak power, approximate to 10-dB gain, 64%-79% peak-power efficiency, and 30%-45% efficiency at 10-dB power back-off throughout this band.