As defined by the FCC's First Report and Order, UWB signals must have bandwidths of greater than 500 MHz or a fractional bandwidth larger than 20 percent at all times of transmission . Fractional bandwidth is a factor used to classify signals as narrowband, wideband, or ultra-wideband and is defined by the ratio of bandwidth at –10 dB points to center frequency. Equation 1-4 shows this relationship.
 The –10 dB point represents the spectral power of a signal at 10 dB lower than its peak power.
where fh and f1 are the highest and lowest cutoff frequencies (at the –10 dB point) of a UWB pulse spectrum, respectively. ...