This book is entitled Microwave and Wireless Measurement Techniques, since the objective is to identify and understand measurement theory and practice in wireless systems.
In this book, the concept of a wireless system is applied to the collection of sub-systems that are designed to behave in a particular way and to apply a certain procedure to the signal itself, in order to convert a low-frequency information signal, usually called the baseband signal, to a radio-frequency (RF) signal, and transmit it over the air, and vice versa.
Figure 1.1 presents a typical commercial wireless system architecture. The main blocks are amplifiers, filters, mixers, oscillators, passive components, and domain converters, namely digital to analog and vice versa.
In each of these sub-systems the measurement instruments will be measuring voltages and currents as in any other electrical circuit. In basic terms, what we are measuring are always voltages, like a voltmeter will do for low-frequency signals. The problem here is stated as how we are going to be able to capture a high-frequency signal and identify and quantify its amplitude or phase difference with a reference signal. This is actually the problem throughout the book, and we will start by identifying the main figures of merit that deserve to be measured in each of the identified sub-systems.
In order to do that, we will start by analyzing a general sub-system that can be described by a network. In RF systems it can be a single-port, two-port, or three-port network.