Electronic Design

Don't Forget The Antenna

If you haven't worked with wireless, you may tend to forget that a really good antenna is required for any radio to work properly. Many times, due to its small and ?mechanical? nature, it's simply taken for granted.

The antenna in a UWB application is critical for good performance, but it presents more than the usual antenna challenges faced by wireless designers. So, rule number 1: Think about the antenna up front as a key part of the system.

There are two basic ways to address the antenna problem?design one yourself or buy one. Want to design an antenna? Well, unless you have considerable experience, it's best to leave that for the experts.

UWB antennas aren't like regular antennas, because they have a much wider bandwidth than the average antenna. Most antennas are resonant and typically have a bandwidth that's only a small percentage of the operating frequency. Bandwidth-widening methods exist, but most end up being unworkable for UWB. Special methods must be used to achieve the desired bandwidth as well as omnidirectional radiation characteristics, not to mention good efficiency and a flat SWR. With the bandwidth of MB-UWB being only about 1.6 GHz rather than the whole 7.5-GHz spectrum, things get only slightly easier.

A common approach is to make the antenna as a copper pattern right on the pc board. Some UWB chip makers already addressed this problem and have recommendations for antennas along with their reference designs. This is a good way to go because the results are proven.

Another approach is to employ a commercial component antenna. Some are available now, and others are on the way. Check with Fractus, Barcelona, Spain, which makes an antenna using fractal technology for the Wireless USB market. SkyCross, another antenna maker, offers a 3D meander line antenna tuned for UWB.

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