Section 4.3. Summary

4.3. Summary

In this chapter, the reciprocity theorem has been used along with basic circuit relationships to evaluate the form of the various parameters of antennas, including effective aperture, effective length, mismatch loss, efficiency, polarization match, and related information. The advantage of the approach presented in this chapter is the formal process through which all the aspects of the antennas and environment can be integrated theoretically. A connection to a link budget form for particular transmit energy spectra or waveforms was also considered briefly. The link budget is expanded in concept in Chapter 2.

The Impulse (I-UWB) implementation of UWB uses impulses, approximated by nanosecond-wide Gaussian pulses, to communicate. For MC-UWB systems, each carrier band can be considered as a separate, narrowband signal. In the latter case, classic link analysis using antenna gain is sufficient. However, the wideband characteristics of the impulse response can be applied to both cases, and still identifies the basic features of antenna transmission needed for the reliability and capacity of UWB communications.

Measurements of different antenna types with both frequency and time domain data were presented to provide insight into the performance of the antenna and the link. In order to provide a better evaluation of the antennas, and also to provide a simple model for link simulation, the singularity expansion method (SEM) was used to characterize the line-of-sight link, specifically the antennas. The theory of the SEM is based on Maxwell's equations and observations of measured data for many pulsed electromagnetic systems. It was found that typical finite sized objects and antennas can be characterized as a set of poles, with residues that describe the angular performance of the structure. This representation leads to a minimal form of modeling that provides both the minimal property and insight into the performance of the antenna systems.

A measurement system was developed for determining the scattering properties of several canonical objects. The scattering for finite-sized objects was described in terms of poles and residues from the measured time-domain system response. A sphere and a cylinder were two of the canonical objects used for characterization. The data collected through transient measurements were postprocessed to obtain the poles and residues and to represent the frequency and time domain nature of the canonical structures.