| In recent years,with the continuous development of underground target detection technology,this technology is widely used in various fields.Ground penetrating radar(GPR),as a convenient and efficient technology with nondestructive detection characteristics,has become the most representative and competitive detection technology among many underground target detection technologies.Antenna is an important part of radar system.Its performance directly affects the detection ability of the radar system.In today’s development trend of GPR,deeper detection depth and higher underground target detection resolution are the main trend and direction of its development.This puts forward new requirements for the design and development of GPR antenna.That is the antenna radiation has better directivity,higher gain and more concentrated beam.In this paper,the research of the spotlight antenna for underground target detection is studied from three directions: antenna,dielectric lens and metamaterial.These research directions are parallel,but the latter two research are the continuation and expansion of the former.The main contents of the paper include:1.The research on antenna is mainly Vivaldi antenna.A dual-slot and dual-polarized Vivaldi antenna which can be applied to GPR is proposed.Aiming at the low gain and poor directivity of traditional Vivaldi antenna at low frequency,the double-slot Vivaldi antenna is composed of two kinds of exponential lines.The inward inclination of the slot lines formed by the two is asymmetric,which can effectively concentrate energy in the main radiation direction,so as to improve the gain and directivity of the antenna.The combination of the two antennas in a cross orthogonal way helps to enhance the ability of the antenna to detect objects in a complex underground electromagnetic environment.The antenna works from0.5GHz to 3GHz and has good directivity and high gain.In terms of time-domain characteristics,the fidelity of time-domain waveform of the antenna is excellent.After the simulation analysis,the antenna is produced and tested to verify the performance of the antenna.2.The research on dielectric lens is mainly divided into two parts.The first part is the research on the spotlight antenna loaded with optical-like dielectric lens.This part is mainly based on the optical principle,and applies the optical lens bunching principle to the design of GPR spotlight antenna.In order to verify the correctness of the method,a dielectric PlaneHyperbolic lens is designed,which is loaded on a dual-slot and dual-polarized Vivaldi antenna.The gain can be increased by 1-2d B at low frequencies,and 8d B can be increased at most in the high frequency range.Due to the insufficient improvement of low-frequency gain,the dielectric lens is improved.A multi-focal dielectric Plane-hyperbolic lens is designed,and a metal reflector is loaded.The simulation results show that the gain of the antenna loaded with multi-focal dielectric Plane-hyperbolic lens and metal reflector is much higher than that of the original antenna other single loaded antennas in the full frequency band,the beam is obviously narrowed,has good focusing effect,well time-domain characteristics and good waveform fidelity.The second part is about the research of the dielectric-loaded director lens.A dual-layer dielectric director lens is designed,which is loaded on a dual-slot and dual-polarized Vivaldi antenna.The results show that the antenna which loaded dielectric director lens at 0.5GHz-2GHz has a strong ability to focus the antenna,the beam width decreases,the maximum increase of gain is about 3d B.At 2GHz-3GHz,the antenna back lobe enlarges and the main lobe width narrows,while the gain decreases from before loading.3.The research on metamaterials is mainly divided into two parts.In the first part,using the in-phase reflection characteristics of artificial magnetic conductor materials.An octagonal annular slot structure is designed as an antenna reflector to improve the directional radiation ability of the antenna.The second part is to design a zero-refraction-index metamaterial lens by using the equivalent parameter extraction method.Combine the artificial magnetic conductor materials reflector and zero-refraction-index metamaterial lens with a dual-slot and dual-polarized Vivaldi antenna.The simulation results show that the gain of antenna with loaded metamaterials antenna is improved significantly at 0.5GHz-2GHz and 2.5GHz-3GHz,especially at low frequency band,and the beam is narrowed and the antenna has well time-domain waveform.Restricted by the bandwidth of the artificial magnetic conductor material,the gain at 2GHz-2.5GHz is lower than that at unload.The antenna is then manufactured and tested to verify the performance of the loaded metamaterials antenna. |
