chapter 14 - Chapter 14 MODERN TOPICS The future has...

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Chapter 14 MODERN TOPICS The future has several names. For the weak, it is the impossible. For the faith- hearted, it is the unknown. For the thoughtful and valiant, it is ideal. —VICTOR HUGO 14.1 INTRODUCTION Besides wave propagation, transmission lines, waveguides, and antennas, there are several other areas of applications of EM. These include microwaves, electromagnetic interfer- ence and compatibility, fiber optics, satellite communication, bioelectromagnetics, electric machines, radar meteorology, and remote sensing. Due to space limitation, we shall cover the first three areas in this chapter: microwaves, electromagnetic interference and compat- ibility, and fiber optics. Since these topics are advanced, only an introductory treatment of each topic will be provided. Our discussion will involve applying the circuit concepts learned in earlier courses and the EM concepts learned in earlier chapters. 14.2 MICROWAVES At the moment, there are three means for carrying thousands of channels over long dis- tances: (a) microwave links, (b) coaxial cables, and (c) fiber optic, a relatively new tech- nology, to be covered later. Microwaves arc I:M wines whose IrequiMicies rnngo from approximately .MX) MH/ to I (KM) Gil/. For comparison, the signal from an AM radio station is about 1 MHz, while that from an FM station is about 100 MHz. The higher frequency edge of microwaves borders on the optical spectrum. This accounts for why microwaves behave more like rays of light than ordinary radio waves. You may be familiar with microwave appliances such as the mi- crowave oven, which operates at 2.4 GHz, the satellite television, which operates at about 4 GHz, and the police radar, which works at about 22 GHz. Features that make microwaves attractive for communications include wide available bandwidths (capacities to carry information) and directive properties of short wavelengths. Since the amount of information that can be transmitted is limited by the available band- 638
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14.2 MICROWAVES 639 width, the microwave spectrum provides more communication channels than the radio and TV bands. With the ever increasing demand for channel allocation, microwave communi- cations has become more common. A microwave system 1 normally consists of a transmitter (including a microwave os- cillator, waveguides, and a transmitting antenna) and a receiver subsystem (including a re- ceiving antenna, transmission line or waveguide, microwave amplifiers, and a receiver). A microwave network is usually an interconnection of various microwave components and devices. There are several microwave components and variations of these components. Common microwave components include: • Coaxial cables, which are transmission lines for interconnecting microwave compo- nents • Resonantors, which are usually cavities in which EM waves are stored • Waveguide sections, which may be straight, curved or twisted • Antennas, which transmit or receive EM waves efficiently • Terminators, which are designed to absorb the input power and therefore act as one-
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chapter 14 - Chapter 14 MODERN TOPICS The future has...

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