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.
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.
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-