Ultra-wideband pulse shaping: bypassing the inherent limitations of the Gaussian monocycle

UWB impulse radio transmissions are power limited as they must respect a frequency mask with low total permitted power and severe isolation requirements for the GPS band. Shaping of the short UWB impulse maximizes transmit power subject to these constraints. We have previously published results for intricate pulse shaping in the optical domain that achieves record levels of power transmission. The most successful pulse shaping techniques in the electrical domain have been achieved with derivatives of the Gaussian pulse shape. The Gaussian monocycle is a low performance choice in terms of transmit power, but nonetheless the subject of intense research activity. In this paper we compare and contrast these UWB pulses, and quantitatively compare their performance in realistic systems (specific RF and antenna hardware). There is the perception that failings in the pulse shape (especially for the monocycle) can be compensated by simple highpass filter and the bandpass nature of the UWB antenna. We fabricate and characterize two UWB antenna designs available in the literature, as well as one commercial antenna. We use our optical pulse shaping device to experimentally investigate the three different pulse shapes and measure their transmitted power spectral density with each of the UWB antennas. We find that the monocycle is significantly less powerful than the others. The fine pulse shaping available in optical processing provides 1.7 to 2.9 dB gain over the electrical processing methods, depending on the antenna used.