The Study Of Vivaldi Antenna Design And Plasma Diagnostic Method

During the process of re-entry into the ground,the aircraft will fly at high altitude in a thin atmosphere,and the aerodynamic heating will ionize the high-temperature plasma to form a plasma sheath,which will hinder the transmission of the EM wave signal transmitted by the aircraft,even it will cause the communication signal to be interrupted,causing the radio blackout.The prerequisite for efficient use of these methods is to obtain parameter distribution of the plasma sheath.In this paper,the microwave reflection method is used to diagnose the electron density distribution of non-uniform plasma.In practical applications,the microwave signal is transmitted through the antenna.Therefore,in this paper,a Vivaldi antenna is designed based on the method of LFM and is used to transmit LFM signal to diagnose the non-uniform plasma electron density distribution.The method above is used to processes the signals transmitted and received by the antenna to obtain the plasma electron density distribution.The contributions of this paper are as follows: 1.In this paper,the microwave reflection method is used to diagnose the electron density distribution of non-uniform plasma in low collision frequency.According to its principle,two schemes are proposed: mixed multi-frequency signal and LFM signal,respectively.The feasibilites of the two schemes are analyzed and their advantages and disadvantages are compared.The LFM signal with a greater advantage is finally selected to diagnose the electron density distribution.2.The design principle of the Vivaldi UWB antenna is studied,and the corresponding UWB antenna is designed based on the range of plasma sheath electron density parameters.Considering existing antenna and engineering implementation of the antenna,the antennas of 2GHz~11GHz and 10GHz~29GHz frequency bands are designed,which performance meets these indicators : good gain,small size,good direction,S11 <-10 dB.3.A simulation study using LFM signal to diagnose non-uniform plasma is carried out.The LFM signal is transmate to non-uniform plasma with Gaussian ascending distribution.The plasma electron density is obtained through a series of processes such as mixing the reflected signal with the transmitted signal,low-pass filtering,adaptive time-frequency analysis,and instantaneous frequency extraction.In this paper,the non-uniform plasma with different magnitude of peak electron density is diagnosed,and the relative electron density distribution is obtained.The distribution is in good agreement with the actual electron density distribution.4.The LFM signal is transmitted to non-uniform plasma through Vivaldi antenna.The LFM signal is transmitted through the antenna to diagnose the non-uniform plasma electron density distribution.Before transmitting the signal through the antenna,the availability of the Vivaldi antenna under the time domain simulation condition is verified,and then an antenna-nonuniform plasma model is established.The antenna of 2~11GHz is chose to transmit LFM signal which frequency increases linearly from 2GHz to 11 GHz to non-uniform plasma,then the data processing method in 3 is used to obtain the distribution of electron density.After analyzing the influencing factors,this result is consistent with the actual distribution.In this paper,the method of using the antenna to tramsmit LFM signal to non-uniform plasma for diagnosing the electron density distribution is studied,and a good result is obtained,which provides an important guidance for the practical application of plasma diagnosis technology.