Solid-state microwave power

Since the 1970s, and even more so since 1985 and the emergence of GaAs power technologies, designers of power amplification functions have had access to solid-state devices (SSPAs for Solid-State Power Amplifiers). Compared with electron tubes, solid-state is generally cheaper and more (sometimes much more) integrated. So, if a function is achievable with transistors, this technology will be preferred; the power vs. frequency of a solid-state function is the first parameter to consider in an analysis like this. However, the comparison may be less straightforward and the criteria more complex. Volume, linearity, noise figure and electrical efficiency in particular are often taken into account [E 1 426] .

How much power can SSPAs deliver? As with tubes, we need to distinguish between technologies: field-effect or bipolar transistor, MESFET, MOSFET or HEMT. In addition, there are two other levels of complexity not found in microwave tubes. On the one hand, highly integrated solid-state devices lend themselves to a variety of arrangements (polarization classes, component assembly, etc.), and the spectrum of possible solutions is vast, the result of compromises between power, bandwidth, linearity and efficiency. On the other hand, elementary transistors offer limited power, and building power amplifiers requires combining them. Paralleling is almost systematic, on a single chip in the case of MMICs, and then between chips.

We describe solid-state performance by adopting a hierarchy of elementary component technology / classes of operation / parallelization. The elements necessary for a good understanding are given, and the reader is referred to [E 1 426][E 1 610]