Modern antenna systems include passive antenna structures, passive microwave circuits and interconnections to electronics. Therefore, the antenna engineer should have a deep understanding of antenna theory and should be able to apply microwave engineering concepts. This textbook provides all relevant material for Master-level courses in the domain of antenna systems. The book includes comprehensive material on antennas and provides a solid introduction into microwave engineering, ranging from passive components to active circuits. We believe that this is the perfect mixture of know-how for a junior antenna expert. The theoretical material in this textbook can be supplemented by labs in which the students learn how to use state-of-the-art antenna and microwave design tools and test equipment, such as a vector network analyzer or a near-field scanner. Several chapters in this book can be used quite independent from each other. For example, chapter 6 can be used in a dedicated phased-array antenna course without the need to use Maxwell-based antenna theory from chapter 4. Similarly, chapter 3 on transmission lines and microwave circuits does not require deep back-ground knowledge in electromagnetics or antenna theory