Other Wireless Systems The two major applications of RF and microwave technologies are in communications and radar=sensor systems. Radar and communication systems have been discussed in Chapters 7 and 8, respectively. There are many other applications such as navigation and global positioning systems, automobile and highway applications, direct broadcast systems, remote sensing, RF identi®cation, surveillance systems, industrial sensors, heating, environmental, and medical applications. Some of these systems will be discussed brie¯y in this chapter | RF and Microwave Wireless Systems. Kai Chang Copyright 2000 John Wiley Sons Inc. ISBNs 0-471-35199-7 Hardback 0-471-22432-4 Electronic CHAPTER ELEVEN Other Wireless Systems The two major applications of RF and microwave technologies are in communications and radar sensor systems. Radar and communication systems have been discussed in Chapters 7 and 8 respectively. There are many other applications such as navigation and global positioning systems automobile and highway applications direct broadcast systems remote sensing RF identification surveillance systems industrial sensors heating environmental and medical applications. Some of these systems will be discussed briefly in this chapter. It should be emphasized that although the applications are different the general building blocks for various systems are quite similar. RADIO NAVIGATION AND GLOBAL POSITIONING SYSTEMS Radio navigation is a method of determining position by measuring the travel time of an electromagnetic EM wave as it moves from transmitter to receiver. There are more than 100 different types of radio navigation systems in the United States. They can be classified into two major kinds active radio navigation and passive radio navigation shown in Figs. and . Figure shows an example of an active radio navigation system. An airplane transmits a series of precisely timed pulses with a carrier frequency fy The fixed station with known location consists of a transponder that receives the signal and rebroadcasts it with a different frequency f2. By comparing the transmitting and receiving pulses the travel time of the EM wave is established. The distance between the aircraft and the station is d c l tR 11-1 where tR is the round-trip travel time and c is the speed of light. 304 RADIO NAVIGATION AND GLOBAL POSITIONING SYSTEMS 305 FIGURE Active radio navigation system. In a passive radio navigation system the station transmits a series of precisely timed pulses. The aircraft .
