Abstract : This thesis is about the improvement of the performances of an ultra wideband (UWB) radar set up for landmines detection. An ultra short high voltage (HV) pulse generator and an impedance matcher device (balun) to be inserted between the 50 Ohm; generator and two-wire antennas 200 Ohm; are particularly detailed. The first chapter shows the principal characteristics of UWB radars and a bibliographical synthesis of the experimental tools necessary for the UWB. The second chapter is devoted to the HV pulse generator based on the technology of a pressurised gas switch (hydrogen). The principle of operation and the characterizations of probes produced for these experiments are also deferred. After various parameter settings, the impulses rise-time can be reduced down to 90 ps, the minimal time duration is of 600 ps, the output voltage and the repetition rate can reach respectively 30 kV and 2,5 kHz. A simulation of the device is compared to the practical results of commutation. In chapter 3, we gathered the studies of the balun and of a voltage amplifier able to supply the generator because these two devices are two transmission line transformers (TLT). The principal defect of the TLT lies in the losses due to the secondary lines. We solved this problem by using ferrite for which we explain process. This study leads to the realization of a ten stages TLT of perfect yield and of a balun whose bandwidth lies between 30 kHz and 3 GHz. A simulation of the experimental results completes the interpretation of the phenomena. Lastly, in chapter 4, the experimental results realized in anechoic chamber relating to the whole emission system thus a few prospects relating to the advance for the system are presented.