12.3.5 Polarization
We saw in Chapter 11 that the polarization of an electromagnetic wave is defined by the orientation of the electric field. In Figure 12.2, it can be noted that the electric field exists in one plane as it moves away from the wire. This means that the wave is plane-polarized. In the case of a wire antenna, and that of most simple antennas, the plane of polarization is parallel to the wire. As we saw in Chapter 11, if the wire is vertical, the wave is vertically polarized; if the wire is horizontal, the wave is horizontally polarized.
The polarization of an antenna is an important property. Clearly, for example, if the current on a vertical transmit antenna results in a radiated field with a vertical polarization, that energy will only be induced into current in the wire of a vertical receive antenna. That is, for wire antennas such as a dipole or monopole, a vertically polarized transmission requires both transmit and receive antennas to be vertical; horizontally polarized transmission requires horizontal antennas, and so on.
Back to reading