Metrology has been the most important aspect of wireless communication ever since the time of Maxwell and Hertz at its very beginning. In fact, the metrology aspects related to radio communications have for decades been one of the driving forces for progress in radio communication. For instance, radar is nothing more than a very good measurement instrument that can be used in important applications such as target identification. Nevertheless, most wireless systems nowadays depend heavily on metrology and thus measurement, for instance new spectrum management, QoS evaluation and green RF technologies, since they are all supported in high-quality wireless radio components. That is why it is important to understand the figures of merit of the main wireless system components, how to measure them, and how to model them. Moreover, with recent advances in software-defined radio, and in future cognitive radio, measurements in time/frequency/analog/digital domains have become a very important problem to microwave and RF engineers. This book is aimed to give engineers and researchers answers at the beginning of their laboratory adventures in microwave, wireless systems and circuits. It can also be used in connection with a graduate class on measuring wireless systems, or a professor can select parts of the book for a class on wireless systems in the broad sense.