2.1 Introduction

The sensors of the principal weapon systems operate by exploiting either electromagnetic energy reflected by the target in the radio-frequency band, or electromagnetic energy emitted by the target in the infrared band. For the better understanding of sensors, some of the theoretical laws on which their performance depends will be recalled.

Only the concepts and formulas needed for a correct understanding of later discussions of radar systems, intercept systems, and noise and deception jamming systems will be reviewed here. Table 2.1 shows the electromagnetic spectrum, from radio waves to millimeter waves (whose wavelength is on the order of millimeters), that is of interest for radar systems.

Table 2.1: The Electromagnetic Spectrum of Interest for Radar Systems