Design And Simulation Of Ultra-wideband Antenna Used For Ground Penetrating Radar

Ground Penetrating Radar is a nondestructive detection tool used for detecting and identifying objects buried underground,which has features such as fast detection speed,continuous data,convenient and flexible operation,high resolution,etc.In recent years,it has been widely used in civil and military fields.Antenna is a crucial part of the GPR system,whose performance directly affects the detecting results.Antennas of a GPR system should have features such as ultra-wideband performance,radiation energy concentration,high fidelity of waveform,small coupling between each other,miniaturization,etc.Unlike other ultra-wideband radars,GPR system requires most of the energy radiating into ground.However,most underground conditions consist of lossy medium that could attenuate signals,and the higher the working frequency is,the stronger the attenuation is.Therefore,in order to enhance investigation depth,a lower emitting signal working frequency is required,which means that the antenna should have UWB characteristic in low frequency band.Based on the requirement of a vehicle-mounted platform which is to realize the detection of deep buried objects underground,this thesis provides two types of bowtie-based UWB antenna working in low frequency band:(1)Three-side-shielded bulbous antenna.Based on the design of traditional bowtie antenna,this design adopts structure loading technique to ameliorate current distribution on antenna surface which obtains smoother input impedance curves and excellent radiation characteristic than bowtie antenna.The modified antenna can work at 131 MHz to 422 MHz frequency range with input impedance around 100 ohms that is easy to realize the impedance matching and conform to the requirements of GPR system.(2)Five-side-shielded antenna with truncated and slot-tuned resistor-loaded arms.This design adopts lumped loading method at the end of antenna and slot-tuned method to guide the current to flow to the lumped loaded elements and to reduce the lowest frequency point and then enlarges impedance bandwidth.Adopting cutting edges and rounding methods can reduce the size of antenna and five-side-shielded cavity can abate the mutual coupling between transmitting and receiving antennas.The working frequency of the designed antenna extends to the range of 10 MHz to 470 MHz and its input impedance is around 150 ohms.It can be used on GPR system based on vehicle-mounted platform.Furthermore,it can be applied to soil,asphalt,concrete,dry snow and other common detecting conditions.The two designed antennas in this thesis both have UWB performance in low frequency band and can easily match with coaxial cables.They can be applied to GPR system used for detecting objects buried deep into ground.Also,the combination of structure loading and lumped loading methods can be applied to other design improvements.