Research On THz Antennas Applied In Borehole

Coal mine water disaster caused by the borehole’s fissures is a great threat to thestate and people’s life and property security. There urgently needs an effective meansto detect the fissures. T-ray imaging technology has the characteristics of strongpenetrability and high resolution, which can be applied to get clear images of fissures.Thus we can easily detect the fissures. T-ray imaging technology has a certainapplication prospect in coal mine. Meanwhile, the T-ray image system in the boreholedemands a THz antenna in front-end, which is requested to be small, integrated withthe drill pipe, and owning narrow beam. This paper focuses on these demands to carryout the corresponding research of THz antenna applied in borehole.First of all, we make a detailed study of miniaturization design of dual-reflectorsand front-fed parabolic reflectors. For dual-reflectors, we make a comparison betweensmall sized Cassegrain form, Gregorian form and the ring-focus form. Small sizedring-focus antenna is found that it has advantage in block effect, longitudinaldimension, sidelobe level (SLL) and input VSWR. A small sized ring-focus antenna ismodeled and simulated, and a narrow beam with the3dB beam-width3oin E planeand3.1o H in plane in110GHz is achieved respectively. For front-fed parabolicreflectors, three types of feeds is designed and analyzed, including dielectric rods,multimode coaxial feed and circular waveguide feed with a rectangular waveguide tocircular waveguide converter. And circular waveguide feed is chose for the THzantenna’s feed finally, because of good performance in beam width, bandwidth andutility. The paraboloid is improved at the same time. A dual-ring reflector is designedaccording to a theory of a multi-ring reflector, and it has reduced the longitudinaldimension. The simulation results show that the dual-ring reflector can help to reducethe3dB beam-width.Secondly, on the basis of the previous research of the front-fed parabolicreflector’ miniaturization design, we take the mechanical structure of the drill pipeinto consideration, and complete the overall design and analysis of the THz antennaintegrated with drill pipe. The simulation result shows the THz antenna’s3dBbeam-width is4.4o in E plane and3.9o in H plane in110GHz, with other electricalparameter such as bandwidth, SLL, VSWR, meets the technical indicators, and leave design margin. The paper provides a way to design THz antennas applied in borehole.