Figure 214 Focused Versus Unfocused Energy

Bare Flashlight Bult>



Unfocused Energy

Focused Energy

Notice that in Figure 2-14, the flashlight bulb on the left radiates light energy in all directions. There is no focusi ng element, and no direction recpives more light: than any other direction. Th e light energy radiated from the bnl'ocused flashlight bulb is similar to the wireless energy radiated from a the oretica I isotropic antenna. An isotropic anten na radiates wireless energy equally in all Erections and does not focus the e nergy in any single direction.

In contrast to thd bare fashhght bulb, the flash light on the right has a reflector behine the bulb. sce reflector focuses the ligh t into a peam that comes out the front of the flashliglrt. The flashlight does not amplify the power or the total amount of light from the flashlight bulb. The flashlight simply focuses the light so that all of it travels in the same direction. By focusing the light, the flashlight provides more directivity (beam-focusing power) for the light energy. Similarly, an antenna provides directivity for the wireless energy that it focuses. Depending on their design, construction, and orientation, antennas focus and radiate their energy more strongly in one favored direction. When they are receiving, antennas focus and gather energy from their favored direction and ignore most of the energy arriving from all other directions.

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