Chapter 4Antennas and Radiation

Antennas are used to convert the currents and voltages generated by the transmitter circuit into electromagnetic fields propagating through space. In the absence of material boundaries that reflect or scatter the waves, the fields propagate in the form of spherical waves, whose amplitudes vary inversely with the distance from the antenna. The field strength and polarization can also depend on the direction of propagation. This variation is described by the antenna pattern function and is one of the characteristics that distinguishes various types of antennas. The other distinguishing characteristic is the terminal impedance. These quantities, and their dependence on frequency, are determined by the shape of the ...

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