| The ionosphere is a part of the atmosphere within a range of 60-1000 km above the earth,which contains a large number of charged particles,it is a natural medium for shortwave communication and has a significant impact on the propagation of radio waves.In order to make full use of it to serve humanity,long-term uninterrupted detection is required,the ionospheric radio detection method is an ancient and economical method,and the VHF ionospheric coherent scattering radar and digital ionosonde are the two most commonly used detection equipment in this method.Antenna system is one of the most important components of these two kinds of detection equipment,and its performance directly determines the accuracy and reliability of the instrument in ionospheric detection.For this reason,this thesis mainly focuses on the antenna system of two kinds of detection equipment,and the main research contents are as follows:Firstly,the basic principle of antenna design and the main parameters to measure the performance of the antenna,including the pattern,gain,input impedance,standing wave ratio,bandwidth and polarization,are introduced in detail.Then the impedance matching of the antenna is analyzed and how to improve the impedance matching of the antenna is discussed.At the same time,the numerical analysis method of the antenna is studied,and the application of the Method of Moments in the antenna design is analyzed.Through the analysis of the transmission characteristics in the high-frequency communication process and the flexible application of the simulation software HFSS used in the antenna design,the necessary preparations are provided for the design and implementation of the VHF ionospheric coherent scattering radar antenna and the digital ionosonde antenna.Secondly,a directional high-gain Yagi antenna suitable for VHF ionospheric coherent scattering radar is designed and implemented to solve the problem that the directional weak gain of the antenna is low.According to the research of the basic structure and working principle of Yagi antenna,and the analysis of the related characteristics of the folded dipole,the initial structure model of the antenna is determined,and the design index of the antenna is given.At the same time,the HFSS electromagnetic simulation software is used to complete the simulation of the antenna and the optimization of the structure.Then according to the final antenna structure model determined by the simulation,the antenna is made,the impedance matching network corresponding to the antenna is designed,and the antenna is tested.The observation results show that the antenna works well and all the performances meet the design requirements.Finally,in order to meet the requirements of the PDI2 agile digital ionosonde to facilitate mobile observation,a broadband high-gain folded dipole antenna was designed and implemented.First,the initial structure model of the folded dipole antenna to be designed is constructed,and the performance indicators of the antenna are given.Secondly,a folded dipole antenna that meets the design requirements is selected through the simulation results of the folded dipole antenna under different lengths by the simulation software.After the size structure of the antenna is determined,the antenna is made.Through the simulation of the gain and standing wave ratio of the antenna at different erection heights,the appropriate height of the antenna is selected.The completed broadband high gain dipole antenna was tested as the antenna of PDI2 ionosonde,and the results show that the designed antenna meets the expected requirements.In summary,this thesis designs and implements a directional high-gain Yagi antenna suitable for VHF coherent scattering radar and a broadband high-gain folded dipole antenna for PDI2 agile digital ionosonde.The observation effect of the antenna on VHF radar is tested,and the observation results are analyzed.The results show that the antenna's various indicators meet the design requirements.Through the design of the folded dipole antenna mounted on the PDI2 ionosonde for testing,the test results prove that the antenna is stable in the frequency range of 1-30 MHz and has good working performance,and meets the requirements of PDI2 ionosonde for mobile observation. |
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