| With the needs of the development of the times,the application range of radar has gradually expanded.According to its use requirements in different industries,it has extended from traditional ground radar to marine radar,aviation radar,drilling radar and other forms.As an important part of the radar,the role of the antenna is self-evident,and its detection performance directly determines the detection ability of the radar.Therefore,improving the detection performance of the antenna has become the primary goal of many researchers.The main purpose of this paper is to use the single-transmit and multiple-receive antenna array to achieve antenna orientation,and to meet the needs of low-frequency and high-bandwidth in the borehole,thereby improving the detection capability of the radar.Since the advent of borehole radar,the optimization of the antenna has always been an important research direction.With the continuous efforts of scholars at home and abroad,the antenna has undergone various improvements,and at the same time,through different loading methods,its performance in drilling has been improved.Also getting better.The purpose of this paper is to discuss the effect of resistive loading on the antenna bandwidth,study the dipole antenna array,select the appropriate size for matching,so that the antenna can also maintain a high bandwidth in a small borehole,improve the radar signal-to-noise ratio and Further improved radar accuracy.From the end of World War II to the end of the 1950 s,the comprehensive theory of antenna arrays was developed;from the 1960 s to the early 1970 s,phased array antennas were re-emphasized and widely used;until the 1970 s,array antennas entered the stage of linear arrays.Circular array,from planar array to conformal array,various antenna technologies have gradually entered the practical stage.In the actual use of borehole radar,due to the limitation of aperture,the overall size of the antenna array is greatly restricted.In order to meet the measurement needs at different frequencies,the bandwidth of the antenna is also tested.At the same time,due to the small interval between the array elements,the accompanying is the mutual coupling between the array elements,which will have a huge impact on the measurement results of the antenna.Usually,we can reduce the effect of direct waves and reflected waves by adding antenna shields and filling them with absorbing materials,but it is obviously not practical for antenna arrays with small apertures,so we can reduce the size of the antenna,In this way,the coupling effect between each antenna unit is reduced.In terms of increasing the bandwidth of the antenna,it is difficult to realize the loading method of the resistance-capacitance mixture.For the dipole antenna,by continuously loading the resistance in the antenna,the internal current of the antenna can be gradually weakened and reduced to zero at the end of the antenna.Achieving the effect of no reflection,this will significantly increase the antenna bandwidth,which is obviously the preferred loading method for dipole antenna arrays.In this paper,the electromagnetic simulation software HFSS is used to simulate the single-transmitting three-receiving dipole antenna array,the resistance-loaded dipole antenna array and the antenna array in the actual drilling environment.series parameters are optimized to obtain better antenna performance.The final simulation results show that by changing the relative size of the receiving antenna and the distributed resistance value of the transmitting antenna,the bandwidth of the antenna array can be effectively increased,the coupling between the antenna elements can be weakened,and the radar signal-to-noise ratio and detection accuracy can be further improved. |
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