3 - Signal excitation

Summary

Introduction

This chapter is devoted to signal excitation for RF characterization. In that respect the main types of excitation used in the microwave field will be presented and their capabilities for wireless-system characterization, identification, and modeling will be explained. The main focus of this chapter is on the generation of special signal patterns and the explanation of the capabilities that those signals bring to the wireless metrology. This approach will complement previous chapters, by explaining how to generate and how to gather important information from specially designed signals. The chapter will start with the one-tone or single-sinusoid excitation.

In linear systems, figures of merit spanning power gain, noise figure, VSWR, band-width, etc. are mainly measured and obtained using a single sinusoid. Since in this type of system superposition laws are valid, the extension of those figures of merit to other forms of excitation that are different from the ones which were used for their identification is valid. So, normally, linear systems' figures of merit are measured using one tone, and then extrapolated very easily to other forms of excitation.

In nonlinear systems this extrapolation is not so simple, and in certain cases it is not even possible, since a nonlinear system does not obey superposition and thus the one-tone excitation is not enough to gather all the characteristics of the nonlinear system.