RF and microwave power amplifiers and transmitters are used in a wide variety of applications including wireless communication, jamming, imaging, radar,and RF heating. This article provides an introduction and historical background for the subject, and begins the technical discussion with material on signals, linearity, efficiency, and RF-power devices. At the end, there is a convenient summary of the acronyms used—this will be provided with all four installments. Author affiliations and contact information are also provided at the end of each part.
Part 1 of this series introduced basic concepts, discussed the characteristics of signals to be amplified, and gave background information on RF power devices. Part 2 reviews the basic techniques, ratings,and implementation methods for power amplifiers operating at HF through microwave frequencies.
The building blocks used in transmitters are not only power amplifiers, but a variety of other circuit elements including oscillators, mixers, low-level amplifiers, filters, matching networks, combiners, and circulators. The arrangement of building blocks is known as the architecture of a transmitter. The classic transmitter architecture is based upon linear PAs and power combiners. More recently, transmitters are being based upon a variety of different architectures including stage bypassing, Kahn, envelope tracking, outphasing, and Doherty. Many of these are actually fairly old techniques that have been recently
made practical by the capabilities of DSP.
Linearization techniques are incorporated into power amplifiers and transmitters for the dual purposes of improving linearity
and for allowing operation with less back-off and therefore higher efficiency. This article provides a summary of the three main families of techniques have been developed: Feedback, feedforward, and predistortion.
The ever-increasing demands for more bandwidth, coupled with requirements for both high linearity and high efficiency create everincreasing challenges in the design of power amplifiers and transmitters.
A single W-CDMA signal, for example, taxes the capabilities of a Kahn-technique transmitter with a conventional class-S modulator. More acute are the problems in base-station and satellite transmitters, where multiple carriers must be amplified simultaneously, resulting in peakto- average ratios of 10 to 13 dB and bandwidthsof 30 to 100 MHz.
提升卡
变色卡
千斤顶
