This book provides a comprehensive overview of fundamental equations and principles of electrodynamics, focusing on electromagnetic waves excited in unbounded space. It explores their characteristics and parameters, delving into the theory of guided electromagnetic waves and the specifics of designing and practically applying feedlines and microwave oscillatory devices of various types. The text also examines radio wave propagation in free space, making it a valuable resource for understanding both theoretical and applied aspects of radio engineering. Intended for undergraduates, specialists, and master's students enrolled in programs such as 210400 "Radio Engineering," 211000 "Design and Technology of Electronic Devices," 210700 "Infocommunication Technologies and Communication Systems," and 210201 "Design and Technology of Radioelectronic Devices," whether studying full-time or part-time.