TABLE OF CONTENTS Each of the various modulation techniques used for ground penetrating radar systems has its relative merits, and in this Chapter we consider the general system architecture and system specifications associated with each.
The most frequently used system design is that of the impulse radar, and the majority of commercially available radar systems use short pulses or impulses which generally come in the category of amplitude modulation (AM). The next most frequently used modulation technique is frequency modulation (FM) followed by synthesised pulse (SPM), holographic (HM) and finally coded and noise modulation (NM). In this Chapter we consider the most commonly used techniques in turn and discuss the key parameters, which need to be considered in the design process.
It is useful to state the relationship between a time domain function f( t) and its representation in the frequency domain f( ?). Fourier transform methods can be used to show
| (6.1) |  |
that is
| (6.2) |  |
The fast Fourier transform (FFT) is often used to compute the transform, but certain well established restrictions must be borne in mind due to its finite limitations. Here we shall consider only the results of applying the Fourier transform over infinite limits.
A real function such as a monocycle is given by the expression
| (6.3) |  |
The Fourier transform of f( t) is given by
| (6.4) |  |
that is,
| (6.5) |  |
and takes the form shown in Figure 6.1. From this it can be seen that the required bandwidth is significant. However,...
