Generation of subnanosecond pulses is a major challenge for UWB communications systems. Several pulse generation techniques for radar applications have been available for years, but most of them do not support the high peak voltage and the pulse repetition frequency required for UWB communications. However, the advancement in semiconductor switching technology has enabled the generation of narrow RF pulses for UWB applications. This chapter discussed the general principles for operation of semiconductor-based UWB pulse generators such as tunnel diodes, step recovery diodes, and drift step recovery diodes. We have intentionally limited our discussion of these pulse generators to an introductory level; interested readers will find cites for detailed examinations of each technique in the references.
Pulses generated from semiconductor switches are either steplike or ramplike impulses. Therefore, they have to go through proper pulse-shaping mechanisms to be converted to the desired UWB pulse shape, whether Gaussian, wavelet, chirp, Hermite, or another shape. To provide a basic understanding of pulse shaping, we have discussed a simple pulse-shaping circuit for generation of Gaussian monocycle UWB pulses. More details on pulse shaping are available in the sources listed in the references.
Another challenge that UWB pulse transmission faces is the radiation of narrow pulses. Although antenna theory for radiating narrowband signals is a mature field, UWB antenna theory is considered an active area of research. This chapter introduced the concept of UWB antennas along with their requirements. We covered topics such as the directionality of antennas and the types of antennas in detail. Furthermore, we explored system network considerations, such as matching and spectral control, as well as directivity and system performance for UWB systems. For further reading, a wealth of information on UWB antennas is available in .