Development Of Transmitter And Antenna System Of Borehole Radar

The borehole radar, as its name suggests, is a ground penetrating radar (GPR) which works in the borehole underground. It is launches electromagnetic wave by transmitting antenna in form of high frequency electromagnetic pulse, and then receives the backward electromagnetic wave by the receiving antenna. According to analysis the backward electromagnetic wave, the borehole radar can find out the specific situations. It is widely used in environmental protection, resources survey, archaeological excavation and many other fields. As the electromagnetic wave producing, transmitting and receiving devices of borehole radar, the performance of transmitter and antenna directly determine the performance of borehole radar. Research into the transmitter and the antenna of borehole radar has a great significance for our country to make up the shortage of the commercial borehole radar’s development and production.According to the specificity and complexity of the work environment of the borehole radar, in this paper, we designed the transmitter and the antenna of borehole radar’s, the transmitter includes a trigger signal generating circuit and a pulse forming circuit. For the antenna borehole radar, we designed a RC hybrid loaded dipole antenna and a planar spiral antenna.The transmitter of borehole radar’s is mainly used the avalanche transistor to design. Using the MARX circuit, a plurality of the avalanche cascaded to obtain a narrow pulse signal with high amplitude, and the short circuited transmission line will be used to make the unipolar pulses into the bipolar pulse. It will be good for the antenna to transmit signals. In the implementation of case, we designed a bipolar pulse signal source, it can make a bipolar pulse with the peak to peak amplitude of 300V, peak pulse width of 4.5ns, the 3dB band of the signal is 25MHz-117MHz, it is suitable for the borehole radar system.The dipole antenna with RC hybrid loading is developed after summarizing the characteristics of the borehole radar antenna. Its loading of Wu-King loading within the 75MHz-500MHz band, its VSWR is less than 1.8. The antenna has more efficiency than pure resistance loaded antenna. At the same time, the transverse dimensions of the antenna is small, the structure of this antenna is simple, it is suitable for time domain pulse radar system.Further, we designed a bow-tie antenna with resistor-loaded. The structure of this antenna is more simple and convenient than general logarithmic spiral antenna. This antenna has a shield which is filled with absorbers for reducing interference from space. The feed network of this antenna is a microstrip balun. The simulation results show that, this antenna can works as a ultra-wideband antenna, the operating frequency of this antenna reaches 0.49 GHz-1.65GHz, its VSWR is less than 1.9, and it’s peak amplitude ratio of receiving signal and tailing signal is less than 10%.