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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 bandwidths of 30 to 100 MHz. A number of the previously discussed techniques can be applied to this problem, including the Kahn EER with class-G modulator or splitband modulator, Chireix outphasing, and Doherty. This section presents some emerging technologies that may be applied to wideband, high efficiency amplification in the near future.
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