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 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. 11.1 and 11.2.
Figure 11.1 shows an example of an active radio navigation system. An airplane transmits a series of precisely timed pulses with a carrier frequency f1. 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 ...