The main characteristic of UWB technology is the use of a very wide frequency range. A system is referred to as UWB system if it operates in a frequency band of more than 500 MHz width, or if the fractional bandwith bw Here f H , f L , and f C denote the upper and lower frequency limit and the centre frequency, respectively. For imaging applications the large bandwidth is of interest because it guarantees a high resolution in range direction, as explained in the next section. UWB systems always

more »

... coexist with other radio services, operating in the same frequency range. To avoid intereference, a number of frequency masks and power restrictions have been agreed internationally. Current regulations are summarized in FCC (2002) ; Luediger & Kallenborn (2009).