Research On Miniaturized Borehole Radar Emission Technology

In the field of underground resource exploration,electromagnetic wave logging is an important means to obtain geological information.Ground-penetrating radar is a kind of electromagnetic wave logging means,and in-well radar system is a kind of groundpenetrating radar system.Compared with the surface ground search radar system,the detection range of in-well radar system is larger and the detection depth is wider.As an important part of the well radar system,the well radar transmitter system directly determines the performance of the well radar system.In this thesis,a pulse source with high output amplitude and a transmitting antenna for miniaturization and compactness of the system are designed.The transmitter source of the well radar system outputs a first-order Gaussian pulse,which has higher instantaneous power,wider frequency band,and larger amplitude.The pulse source designed in this thesis uses an avalanche tube to generate a zero-order Gaussian pulse,and increases the amplitude of the output pulse by MARX cascading,and then uses reflective line coupling to generate a first-order Gaussian pulse,finally realizing a miniaturized high-output amplitude pulse source with a width of 33 mm,a length of320 mm,a center frequency of 51.6 MHz,and an output amplitude of 1797 V or more.Then the internal resistance of the pulse source was tested to facilitate the design of an antenna with corresponding input impedance.The transmitting antenna of the radar transmitting system in the well is a dipole antenna with an asymmetric design.The left oscillator of the antenna is a hollow copper cylinder,which can hold the Gaussian signal source and other components of the in-well radar system.The right-hand side of the antenna is a five metal patch,with the length of the patch reduced in sequence,while resistors are loaded at the end of the patch to broaden the operating band.The external sealing tube of the antenna is made of FRP tube to improve the structural strength and waterproof capability of the transmitting antenna.The final design of the antenna has a total length of 3393 mm and a diameter of 42.5 mm.in addition,for the different working environments faced by the radar system in the well,the working performance of the transmitting antenna in different conductivity mud,different boreholes and different environmental media is studied,and it is proved that the antenna has a good performance in the frequency range of 30-200 MHz in the actual working environment.Finally,a summary of the whole thesis is given,indicating the features and the areas to be improved in this thesis,and looking forward to the future of radar transmitting system in wells.