The aim of this paper is to investigate the parameters of one of the UWB Sensors, called Vivaldi Antenna, and to propose the new ways how they can be improved. As a practical implementation of the sensor, the UWB radar for wall penetrating applications with impulse excitation was utilized. For wall penetration low frequency (0.3 – 8 GHz) supporting UWB signals are required. Within the scope of this project, the Vivaldi antenna parameters are improved in order to optimize the radiation bandwidth with an usable gain response along the whole operating band, including lower frequencies. It also automatically leads to the optimization of the size of the antenna. In addition, an investigation of the phase linearity and UWB behavior of the antenna was carried out.