Telex 38109-977 manual Waves that are in phase combine to form a larger wave

Figure 7.5 The orientation of the radiator (antenna) determines the polarization, and therefore, the orientation of the E and H fields.

EField Vertical

HField Vertical

H Field	E Field
Horizontal	Horizontal
VERTICALLY	HORIZONTALLY
POLARIZED WAVE	POLARIZED WAVE

Transmit and receive antennas of the same system must be oriented in the same direction (plane) to have a proper transfer of the carrier. In theory, if a transmit antenna is oriented vertically, thus producing a vertically polarized carrier, and the corresponding receive antenna is oriented horizontally, the receive antenna will not be able to see the vertically polarized wave at all. In practice, there will always be some polarization shift in the path and the receiver will see a very small signal if it is close enough to the transmitter. To avoid this problem, antennas in a given RF system should always have similar orientation.

There are other forms of polarization, such as circular polarization, which can be used to help counteract the effect of multipath, but for now we will use horizontal and vertical polarization for our discussion. It is important to note here the difference between polarization and phase, as the two terms are often confused. Phase refers to the relationship of the sinusoidal energy of two or more waves, not to the orientation of the electrical component. See Figure 7.6. Two identical waves that are in phase, and are combined, add to make a larger wave. Two identical waves that are out of phase by exactly 180°, and are combined, cancel each other out. See Figure 7.7. Waves that are not exactly identical in either frequency, amplitude, or phase will have a composite sum that may increase the overall amplitude at some points, and either reduce or eliminate the overall amplitude at others. See Figure 7.8. It is critical to have a good understanding of these two principles as we start to discuss multipath.

Figure 7.6 Waves that are in phase combine to form a larger wave.

Figure 7.7 Waves that are out of phase cancel each other.

C h a p t e r 7 - D e s i g n o f W i r e l e s s I n t e r c o m S y s t e m s 99