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The antenna is probably the most overlooked part of an RF design. The range, performance, and legality of an RF link are all critically dependent upon the antenna. However, antenna placement is often left until the end of the design process, when it is expected to fit into whatever space remains, regardless of the impact on performance. Many such designs ultimately accept degraded performance or are forced to undergo multiple redesigns.

The antenna is one of the most complicated aspects of RF design. With so many interdependent variables, application becomes as much art as science. Engineers delving into RF design for the first time can quite easily confuse or misinterpret the meaning of antenna specifications and how to apply them. For instance, the gain of an antenna is very different from the gain of an amplifier. One of the most common misconceptions is that the radiation pattern reported on an antenna's data sheet will match the radiation pattern of the antenna on the final product. In actuality, the radiation pattern for a quarter-wave monopole antenna, for example, is so critically dependant on the design and layout of the product that manufacturers' gain specifications and radiation pattern plots have little use other than to ascertain potential antenna performance.

Since voluminous texts have been written about each of the many antenna styles, it is unnecessary to cover them all here. Instead, this article will focus only on the antenna styles commonly used in low-power handheld products: dipole and monopole whips. These styles cover a wide range of available antennas and are among the most common to be implemented incorrectly. With that in mind, the article will also share some rules of thumb that can be applied to designing with antennas.

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•Full Article: Understanding Antenna Specifications And Operation