Modern wireless communication systems require broadband microwave high-power and high-efficiency amplifiers with good linearity to support high data rate transmission using higher-order modulation techniques. Worldwide efforts toward decarbonized society demand highly efficient microwave power amplifier devices. In addition to this, space use demands small size and lightweight systems to reduce overall system cost. Gallium nitride (GaN) technology, a III-V group semiconductor technology, has all the attributes for space use and making toward decarbonized society outperforming its competitive technology LDMOS at higher microwave frequency. Thus, GaN has become the preferred microwave and mm wave frequency compound semiconductor replacing others for high-power and high-efficiency applications, for example 5G and next-generation cellular base stations. Appropriate circuit design using GaN devices is required to take all advantages of GaN semiconductor. This book discusses design and analysis of microwave highpower and high-efficiency amplifiers for communications, appropriate for undergraduate, postgraduate students, practical circuit designers and researchers in the field of electronics and communication engineering. This textbook will focus on properties of GaN materials and design of GaN transistor-based microwave amplifiers operating in different classes of operation such as Class-A, B, AB, F and F–1 suitable for various high-power and high-efficiency applications. This book will elaborate the extended continuous Class-F and Class-B amplifier operation for broadband performance maintaining higher power and higher efficiency. Various types of impedance matching techniques and thermal design of high-power amplifiers are also discussed in this book. Each chapter is supplemented with suitable schematic diagrams, analytical expressions, plotted results and solved numerical examples. This textbook has evolved from the author’s design and development experience on microwave amplifiers, linearizers and other microwave active circuits for Indian national satellite communication systems at Space Applications Center, Indian ix