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Appendix B. Antenna Radiation Patterns

This appendix contains many of the common WLAN antennas that are used in the industry today. Several companies produce antennas that are widely used by the various WLAN product vendors. Some original equipment manufacturer (OEM) antennas might have different company logos put on them, as well as proprietary antenna connectors.

Each antenna in this appendix is supplied with a polar plot chart, showing the radiation patterns, as well as physical specifications. Because physics convey how antennas radiate, antennas of similar style (omni, patch, and so on) and similar gain, from different vendors, will usually have similar attributes to those depicted here.

For those of you who are not familiar with a polar plot, they are very simple to use. As discussed in Chapter 2, "Understanding RF Fundamentals," linear antennas have two radiation planes, referred to as the horizontal and vertical planes. Omnidirectional antennas, which radiate in a full circle around them, have a 360-degree beam width in the horizontal plane (when installed properly). In many cases, an omni antenna will not include a horizontal plot if the radiation pattern is uniform in its horizontal plane for the full 360-degree plane.

Another specification that is sometimes listed in directional antennas is the front-to-back or front-to-side ratio. This is a ratio, measured in decibels, of the maximum signal level in the main lobe, compared to the maximum signal level either at 180 degrees (front to back) from the primary energy lobe, or at 90 degrees (front to side) from the primary lobe.

The antenna depicted in Figure B-1 and Figure B-2 is known as a Yagi antenna. A Yagi antenna is a unidirectional antenna commonly used in communications when a frequency is above 10 MHz, and consists of two or more straight elements, each measuring approximately 1/2 electrical wavelength. The Yagi in Figure B-2 has a beam width of 25 degrees horizontal and 30 degrees vertical. When describing a beam width, the edges of the main beam are identified as the points where the energy is 3 dB below (Points A and B) the peak energy point (Point C).