Abstract : Radio communications using very broad frequency bands (UWB) have been developed rapidly since the early 2000s. This technique has advantages that made it attractive in many civil and military applications. The aim of this thesis is to design and characterize miniature Ultra Wide Band antennas in the time domain for the lower part of the frequency band (0.1-2 GHz).
First, a new UWB antenna has been designed: the folded wire monopole antenna. This very simple and small size structure has naturally high bandwidth and quasi-omnidirectional radiation pattern over its entire band of operation. We develop an analytical model describing fast and accurate behavior of this antenna which enabled us to understand the role of different parameters of the antenna. There is excellent agreement between the results obtained by this model and those obtained by numerical simulation. With this analytical model, we can optimize the performance of the folded wire monopole for the low frequencies in two different ways: by thickening the diameter of radiating wires or by adding stubs. Both new antennas have been characterized and they have the same radiation characteristics, but a different matching.
Typically, UWB antennas are characterized in the frequency domain (radiation pattern and antenna matching). However, a more adequate approach might be preferred: Ultra Wideband antennas can be described in the time-domain. We have introduced new descriptors which are used to quantify the distortion introduced by the antenna: fidelity function and time-domain gain. Time and frequency domain measurements have been performed. Measurements on the different versions of the folded wire antenna showed a good agreement with the simulations in terms of both frequency and time domain characterization.
Finally, we have developed a very effective time domain technique measurement by using time domain reflectometry. This method gives very good results in terms of radiated pulses and antenna matching