Introduction

Power amplifiers (PAs) are usually the last active component in the RF chain in modern radar and telecommunication equipment. Their nonlinear behavior has a significant impact on the overall system performance and quite often is the most limiting factor in modern radio systems. The purpose of a power amplifier is mainly to boost the radio signal to sufficient power levels suitable for a wired or wireless transmission from the transmitter to the receiver. Typically, they work at relatively high power levels and hence are a major power consumer in the overall transmitter system. However, their conversion efficiency from DC supply power to RF output power is traditionally very poor. Further, it is strongly dependent on the RF signal drive level and highest when the amplifier is operated in its most nonlinear region and the output RF power compressed or even saturated. Efficiency and linearity are severely contradicting power amplifier requirements and the most important parameters to be traded off.

One of the biggest selling factors for mobile handsets is ‘talk time.” For other battery operated systems such as wireless sensor networks or even satellites the ‘time in operation’ is commercially a highly valued asset. For fixed wireless transmitter systems (e.g., base stations) the running cost and the electricity bill are commercially most relevant, they translate directly into carbon footprint and related CO2 emission. Most military platforms that are capable of carrying a modern radar system are limited in space, energy and cooling capability, hence the efficiency of the radar transmit power amplifier mostly determines the performance and size of the radar equipment that can be implemented on a given platform. The overall efficiency of a power amplifier subsystem is highly commercially relevant and detailed system requirements and tradeoffs need to be well understood when deciding on a power amplifier architecture.