Correlation based pattern stability analysis and a figure of merit for UWB antennas

Combining the concepts of pulse fidelity, time-domain correlation patterns, and,frequency-domain pattern stability, we propose the concept of frequency-domain correlation patterns and a figure of merit, called pattern stability factor (PSF), to characterize pattern stability of wideband antennas. The frequency-domain correlation pattern represents the relationship between radiation in a reference direction to radiation in all other directions of interest, over a specified bandwidth. With practical examples, we demonstrate that this tool is very useful when selecting a single transfer function (and a reference direction) for the antenna when designing or optimizing an ultrawideband (UWB) system. Careful selection of the reference direction is crucial for antennas with relatively less stable patterns, but even antennas with relatively stable patterns can perform poorly overall if an inappropriate reference direction is chosen. The PSF represents the overall pattern stability of an antenna for a specific bandwidth and a range of directions. It is useful as a quantitative measure: a) to compare the suitability of different antennas for a given wideband or multiband application; b) to assess pattern stability improvement methods; and c) to quantify the effect of packaging, etc., on stability. We also propose the concept of PSF bandwidth and show how it can be used to identify stable frequency bands of a given antenna within its impedance bandwidth, and how it compares with the impedance bandwidth of some UWB antennas.