Chapter 8Wideband Antennas 1




Wideband is a relative term used to describe a wide range of frequencies in a spectrum, typically from 10% to one octave and sometimes more than a decade bandwidth. This bandwidth is related to a characteristic of the antenna; in general this refers to matching, but it can also equally refer to polarization or radiation pattern.

There are essentially two main applications for wideband antennas. The first is related to the world of radar. In order to detect an object which would be hidden at certain frequencies, it is important to illuminate the targets with a wideband signal. Similarly, for reasons of accuracy in localization with pulse radars, as narrow a pulse as possible must be produced in order to increase the range resolution. It is therefore necessary in this case to widen the frequency bandwith.

The second reason is linked to the definition of channel capacity [SHA 49]. With a workable signal-to-noise ratio, capacity is thus proportional to bandwidth. The new video signal standards, such as MPEG-4, require high transmission rates and therefore a wide frequency band. Spread spectrum modulation techniques similarly require wide frequency bands. In recent years, applications classified under the acronym UWB (ultra-wideband) have become known as a result of numerous developments in localization and communication for the two reasons stated above.

There are several possible strategies for antenna design. The choice of design approach depends ...

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