A method and system shapes a spectrum of an impulse radio signal, such as an UWB signal. First, basis pulses at various frequencies and pseudo-random delays are generated. The generated set of basis pulses are then weighted and delayed, and combined linearly to conform the spectrum of the transmitted basis pulses to a spectral mask. The spectral mask can be predetermined, or the conforming can be adaptive. Furthermore, the basis pulses can be frequency-shifted before the combining.