Advances in Microwaves, Volume 5 is a three-chapter text that covers low microwave frequencies used to accelerate elementary particles and centimeter and millimeter waves for exploring atmospheric phenomena, as well as the microwave demodulation of light. Chapter 1 describes high-speed photodetectors whose modulation frequency response extends into the microwave region. This chapter focuses on the fundamental principles of specific detectors whose performance is sufficiently close to fundamental limits to assure their staying power. Chapter 2 examines radiometric fundamentals associated with the frequency spectrum, with particular emphasis on the 3 cm to 3 mm wavelength region. Chapter 3 discusses the conditions in which hybrid waves traveling at the velocity of light can exist in a homogeneous isotropic medium. This chapter also explores the design requirements of deflectors. Discussions on transformation of Maxwell’s equations for a traveling wave in a gyroelectric or gyromagnetic medium and consistent solutions of the scalar wave equation are provided in the supplementary texts.