This thesis covers techniques for robust analysis, design, fabrication and characterization of ultra-high efficiency microwave switched-mode power amplifiers (PAs) in the range of 8--12 GHz, using different active device technologies and with efficiency in the 70% range with output power ( POUT) 0.5--1 dB below the maximal power available from the device (PMAX). Applications include spatial power combining, power control and linearization, tunable and reconfigurable PAs and multistage PA configurations. Three main methodologies for the PA design were explored: (1) a low-frequency class-E theory approach with linear model parameter extraction; (2) nonlinear simulations; and (3) the load-pull technique.; Using different paths of the established design methodology, a number of reliable X-band class-E PAs are designed and characterized. A class-E PA is applied as an element in a spatial combiner in order to solve the heat generation problem. A broadband radiating element and a uniform feeding/biasing network allow for an ultra-high amplification and power combining efficiency of an antenna array. This array represents a unique solution for efficient power combining in X-band frequency range.; Nonlinear active device modeling issues are also addressed and a comparison between simulation and measurement is performed. It is shown that existing nonlinear device models do not accurately predict switched-mode or ultra-linear PA behavior and cannot be used for dependable design. Therefore a load-pull based methodology is applied to high-power ultra linear amplifier design in commercial wireless communications. The same methodology is used for the development of highly efficient power amplifiers in the microwave range.; In order to improve the gain of a switched-mode microwave power amplifier, a two-stage amplifier is designed, fabricated, optimized and characterized, showing significant improvement in gain with minimal decrease in overall efficiency.; The most important component in a switched-mode PA is the active device itself, and its performance has the greatest impact on final PA characteristics. Three main active device technologies are compared for their suit ability for switched mode microwave amplifier design. Using the methods presented in the previous chapters, several amplifiers were designed, fabricated and characterized. Results are organized in terms of relevant parameters and the benefits that each transistor family offers are studied. (Abstract shortened by UMI.)
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