Hybrid microwave power amplifier design

This article is dedicated to the hybrid microwave power amplifiers and to their design. It aims at giving an overview of the topic as complete as possible, although it does not expect to be exhaustive, given the complexity of the subject. Thus, an attempt was made to collect any useful information about hybrid power amplifiers from the designer's point of view. A summary of applications of hybrid power amplifiers is then provided, giving a comprehensive idea of the diffusion of such systems and of their employment according to different power level and frequency bands at which they are required to operate. From a strictly theoretical point of view, this article reports the main characteristic parameters of power amplifiers and their classification as derived from the traditional theory. A distinction between bias classes and operating classes is provided, recalling with some mathematical details different operating modes, in particular current mode and switched mode operations. Apart from mathematical-based statements, this article addresses practical aspects that are essential in the design of a hybrid power amplifier, considering its elementary components and providing a description and an essential bibliography for each of them. Starting from the printed circuit board, which physically constitutes the amplifier, the active components (transistors) and passive components (discrete and distributed) are described, and some considerations about the final assembly are given. Finally, some design examples are provided: In particular, the design of a hybrid microwave power amplifier is detailed step by step, from theoretical aspects to the realization process.