The foundation for radar systems in general was laid by Christian Hülsmeyer when he obtained the worldwide first patent in radar technology on April 30, 1904 (patent DE 165 546). Six years later Gotthelf Leimbach and Heinrich Löwy applied for a patent to use radar technology to locate buried objects with radar technology (patent DE 237 944). This system used surface antennas together with a continuous-wave radar. In 1926, a pulse radar system was introduced and filed for a patent (DE 489 434) by Dr.
The underground mining operation for raw materials is planned and monitored by geological measurements. One method is drill-core analysis, whereas borehole radar systems are primary tools to map the surrounding area of the borehole. Nowadays mostly borehole radar systems with omni-directional receiving antennas are utilized. These systems can only measure the reflector distance, whereas directional antennas can estimate the azimuthal angle additionally. The antenna dimensions are limited by the borehole diameter.