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RF and Microwave Power Amplifier and Transmitter Technologies — Part 1
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Short Description: The arc transmitter, largely attributed to Poulsen, was a contem- ..... power of the transmitter. Since peak power is needed only in the worst- ...
Content Inside: High Frequency Design From May 2003 High Frequency Electronics Copyright © 2003 Summit Technical Media, LLC RF POWER AMPLIFIERS RF and Microwave Power Amplifier and Transmitter Technologies — Part 1 By Frederick H. Raab, Peter Asbeck, Steve Cripps, Peter B. Kenington, Zoya B. Popovic, Nick Pothecary, John F. Sevic and Nathan O. Sokal With this issue, we begin a four-part series of articles RF and microwave lope tracking, outphasing, and Doherty. power amplifiers Linearity can be improved through techniques and transmitters such as feedback, feedforward, and predistor- that offer a comprehensive are used in a wide variety tion. Also discussed are some recent develop- overview of power amplifier of applications including ments that may find use in the near future. technologies. Part 1 covers wireless communication, A power amplifier (PA) is a circuit for con- the key topics of amplifier jamming, imaging, radar, verting DC input power into a significant linearity, efficiency and and RF heating. This amount of RF/microwave output power. In available RF power devices article provides an intro- most cases, a PA is not just a small-signal duction and historical amplifier driven into saturation. There exists background for the subject, and begins the a great variety of different power amplifiers, technical discussion with material on signals, and most employ techniques beyond simple linearity, efficiency, and RF-power devices. At linear amplification. the end, there is a convenient summary of the A transmitter contains one or more power acronyms used—this will be provided with all amplifiers, as well as ancillary circuits such as four installments. Author affiliations and con- signal generators, frequency converters, mod- tact information are also provided at the end ulators, signal processors, linearizers, and of each part. power supplies. The classic architecture employs progressively larger PAs to boost a 1. INTRODUCTION low-level signal to the desired output power. The generation of significant power at RF However, a wide variety of different architec- and microwave frequencies is required not tures in essence disassemble and then only in wireless communications, but also in reassemble the signal to permit amplification applications such as jamming, imaging, RF with higher efficiency and linearity. heating, and miniature DC/DC converters. Modern applications are highly varied. Each application has its own unique require- Frequencies from VLF through millimeter ments for frequency, bandwidth, load, power, wave are used for communication, navigation, efficiency, linearity, and cost. RF power can be and broadcasting. Output powers vary from 10 generated by a wide variety of techniques mW in short-range unlicensed wireless sys- using a wide variety of devices. The basic tems to 1 MW in long-range broadcast trans- techniques for RF power amplification via mitters. Almost every conceivable type of mod- classes A, B, C, D, E, and F are reviewed and ulation is being used in one system or anoth- illustrated by examples from HF through Ka er. PAs and transmitters also find use in sys- band. Power amplifiers can be combined into tems such as radar, RF heating, plasmas, laser transmitters in a similarly wide variety of drivers, magnetic-resonance imaging, and architectures, including linear, Kahn, enve- miniature DC/DC converters. This series of articles is an expanded version of the paper, “Power Amplifiers and Transmitters for RF and Microwave” by the same authors, which appeared in the the 50th anniversary issue of the IEEE Transactions on Microwave Theory and Techniques, March 2002. © 2002 IEEE. Reprinted with permission. 22 High Frequency Electronics
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