The radio-frequency engineering recently has gone through extensive development. Software-Defined Radio (SDR) plays an important role in this development, bringing new possibilities to radio-frequency engineering and enables us to look at existing radio technologies in a new, innovative way. One such technology is a Doppler antenna, which allows us to find the direction from which the radio signal of given frequency is being transmitted. The SDR allows us to design and construct a highly-simplified system based on the Doppler antenna array. This paper deals with the design and implementation of such system used for the localization using the Doppler effect and the tests of the designed Doppler antenna system.