Communications, Radar & Electronic Warfare (201.. - Index of

Communications Electronic Warfare 299detect have also continued to change, to include frequency hopping and spreadspectrum systems. These developments are discussed further in this chapter.17.3.3 Op erational Uses of DF SystemsDirection finders are used in a wide variety of applications, including:• radio monitoring;• passive EW against enemy transmissions;• air traffic control;• maritime traffic control;• radar Warning Receivers for platform self-protection;• localisation of specific platforms on the battlefield, particularly systems such as airdefence and surface search radar, also enemy command and control, special forces,etc;• localisation of network subscribers in a mobile network. This can be achieved bydetermining which base station is serving the mobile, but direction finding provides afar better estimate of location.We will now look at the basic principles of DF.17.3.4 Basic Principles of DFDirection finding is based on the theory that at a distance from a radiating antenna, theadvancing wavefront is effectively perpendicular to the direction of travel at anyreasonable distance, as illustrated in Figure 17.16. The waves radiate out in all-+++++--------------------------------+-+++++-+-1-1--.-Very close to the antenna. wavefront IS Circular(for omnl-dlrectlonal antenna)At greater distances, radiUS of wavefront ISso large that wavefront IS effectively straightFigure 17.16 At long ranges, the radius of emission becomes essentially a straight line. This canhowever be modified by diffraction around terrain and building features.