RF Theory

Radio frequencies are high-frequency AC signals radiated into the air via an antenna, creating radio waves. Radio waves propagate away from the antenna in a straight line in all directions at once, just as light from a light bulb does. And, just as more light bulbs spread around a room provide better overall lighting, more antennas spread around a room provide stronger RF signals for mobile clients.

Phenomena Affecting RF

When radio waves hit a wall, door, or any other obstruction, the signal is attenuated, or weakened, which might result in reduced throughput. The following natural phenomena affect RF signals, as illustrated in Figure 9-2:

■ Reflection: Occurs when the RF signal bounces off objects such as metal or glass surfaces.

■ Refraction: Occurs when the RF signal passes through objects such as glass surfaces and changes direction.

■ Absorption: Occurs when an object, such as a wall or furniture, absorbs the RF signal.

■ Scattering: Occurs when an RF wave strikes an uneven surface and reflects in many directions. Scattering also occurs when an RF wave travels through a medium that consists of objects that are much smaller than the signal's wavelength, such as heavy dust.

■ Diffraction: Occurs when an RF wave strikes sharp edges, such as external corners of buildings, which bend the signal.

■ Multipath: Occurs when an RF signal has more than one path between the sender and receiver. The multiple signals at the receiver might result in a distorted, low-quality signal.

Figure 9-2 RF Phenomena

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