Application of UWB Antenna Descriptors to Antenna Performance Assessment

Ultra-wideband systems (UWB) are exploiting a large frequency band. Ranging from 3.1 to 10.6 GHz, they have a fractional spectrum of more than 20%, as defined by Federal Communications Commission (FCC). Several antenna performance descriptors, such as input impedance bandwidth, gain, beamwidth or effective antenna length, can face strong frequency dependence. In this context, the traditional narrowband approach to antenna design is no more appropriate for UWB antennas. Moreover, the frequency dependence of the radiation pattern produces that antennas behave as temporal and spatial filters, radiating differently distorted time-domain waveforms in different directions. For the same excitation, the comparison of two antennas radiating two different waveforms, is almost impossible. For all these reasons, a more compact time domain antenna descriptor without frequency and direction dependence is needed. In this sense, the compactness of the descriptor means that it should summarize the performance of the antenna (or antenna system) in a single parameter, in order to simplify its design using optimization techniques

Lamensdorf used a time domain approach, defining signal fidelity as a measure of distortion, based on cross-correlation of compared signals. McLean also defined new pattern descriptors for UWB antennas (correlated energy pattern and correlation coefficient pattern), useful in systems with correlation detection. These descriptors consider a single antenna and indicate how the radiated UWB signals will change with the time and as a function of direction.

Our proposal is to characterize antennas for UWB applications, using figures of merit that do not depend on direction. Figures of merit applied to a single antenna in free space, as well as to a complete transmitter-receiver system will be presented and applied to actual antennas through electric field measurements.