Design And Research Of Antennas Borehole Radar System

As a standard fittings in wireless communication system, antenna is one of important basic devices, whose position and role just like human eyes and ears. Therefore, to make sure long distance and clear communication is essential in communication system. Borehole radar antenna, as a new-type antenna working in deep well, is attracting large numbers of attentions in the field of ground penetrating radar system. Compared to other antennas, the borehole radar antenna has its own advantages, such as underground working and high resolution ratio. In borehole radar system, we usually utilize an omnidirectional antenna to send pulse signal and use a directive antenna to detect reflective signals.The main purpose of this work is to design the low-frequency borehole radar antennas, and based on theoretical analysis, numerical simulation experimental measurements, to analyze their performances, thereby seeking bandwidth suitable antenna and conducting simulation test.This thesis have designed three type of borehole radar antennas:The first one, due to the bradenhead may restrict the radar system, was designed as a simple half-wave doublet antenna. The working band of a simple half-wave doublet antenna is settled down, thereby obtain the central frequency, and figuring out the wavelength. The simulated results have demonstrated that the resistance value of a fixed frequency mainly relies on the antenna radius when its length is fixed. But, admittedly, the bandwidth of the antenna depends on its length.The second one was a resistances loaded symmetric half-wave antenna, where the resistances were loaded on the gaps between two segments. This thesis have presented two different load method:one is equidistance and the other one is non-equidistance. The simulated results showed the bandwidth was too narrow for the first one; however, compared to the first one, the second one can obtain suitable bandwidth. Moreover, the second one can make sure the reality of the received pulse signal.Based on the resistances loaded antenna, the third antenna was to load a new-type absorbing material ferrite as a carinal cavity, where the ferrite can absorb or decay the electric radiation from the free space so that decrease significantly the reflective wave. Compared to the resistances loaded symmetric half-wave antenna, the simulated results of this antenna lowered the working frequency from the original 160 MHz-180 MHz to below 100 MHz, and the working bandwidth were broaden about 20-40 MHz. The further experimental results showed that this absorbing material loaded antenna works at 40 MHz to 80 MHz, well coincided with the simulated results. The simulated directional diagram demonstrated that antenna has been transferred from omnidirectional antenna to directional antenna after loading the absorbing material. Therefore, the radiation gain has been enhanced.The simulated and experimental results presented here demonstrate that the proposed borehole radar antenna promise to find its real-world significances and applications in the ground penetrating radar system.