Xian Ling Liang

126 Ultra Wideband – Current Status and Future Trends

[40] Lu H., Xu T., Lakshmanan M. and Nikookar H., Cooperative wavelet communication for multi-relay, multi-scale and multi-lag wireless channels, *Proc. of IEEE Vehicular* 

*Technology Conference (VTC)*, Budapest, Hungary, May, 2011, pp. 1-5.

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/47805

## **1. Introduction**

Ultra-wideband (UWB) antennas are gaining prominence and becoming very attractive in modern and future wireless communication systems, mainly due to two factors. Firstly, people increasingly high demand for the wireless transmission rate and UWB properties such as high data rate, low power consumption and low cost, which give a huge boost to the UWB antennas' research and development in industry and academia since the Federal Communications Commission (FCC) officially released the regulation for UWB technology in 2002. Secondly, now the wireless portable device need antenna operated in different frequencies for various wireless transmission functions, and operation bands and functions are increasing more and more, which may result in challenges in antenna design, such as antenna space limitation, multi antennas interference, and etc. One UWB antenna can be used to replace multi narrow-band antennas, which may effectively reduce the antenna number.

The bandwidth is the antenna operating frequency band within which the antenna performances, such as input impedance, radiation pattern, gain, efficiency, and etc., are desired. The most commonly used definitions for the antenna bandwidth are the fractional bandwidth (for narrow or wideband definition) and the bandwidth ratio (for ultrawideband definition).

The fractional bandwidth is defined as

$$BW = \frac{f\_h - f\_l}{f\_c} \times 100\% \tag{1}$$

The bandwidth ratio is defined as

$$BW = \frac{f\_h}{f\_l} \colon 1 \tag{2}$$

© 2012 Liang, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Liang, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*fl* – the lower frequency of the operation band. *fh* – the higher frequency of the operation band. *fc* – the center frequency of the operation band.
