Beam Pointing Error And Correction Method Of Phased Array Antenna Under Plasma Sheath

In the process of super high speed flight near the space,the surface of the aircraft rubs violently with the air,forming plasma sheath around it.Because plasma sheath is a kind of lossy and dispersive medium with complex dielectric coefficient,and it has strong nonuniform distribution characteristics,when the phased array antenna installed in the tail of the aircraft radiates outward,the plasma sheath will affect the beam direction of the antenna.It mainly includes three aspects:(1)the existence of plasma sheath will increase the coupling effect between array antennas,resulting in the increase of beam forming error;(2)the plasma sheath will change the direction of arrival of the target signal,resulting in the difference between the estimated direction of arrival and the actual direction of arrival of the target,affecting the effect of beam synthesis;(3)the multi-path effect between plasma sheath and aircraft,changing the field strength The pattern distortion of the antenna is caused by the distribution,and the beam synthesis is finally affected.Around this problem,this paper mainly includes the following aspects:1.According to the time and space distribution of the parameters such as the flow and material characteristics of the plasma sheath on the surface of the aircraft,the electronic density near the antenna during the whole flight,and the collision frequency,a threedimensional electromagnetic simulation model of the phased array antenna with plasma sheath is established,and the electromagnetic calculation of the three-dimensional flow field is carried out,and the validity of the calculation model is analyzed.2.The radiation characteristics in the near field of phased array antenna with different plasma sheath parameters are calculated by using the simulation model,and the beam direction is calculated according to the results of antenna pattern.The relationship between the beam direction deviation angles of phased array antenna with different plasma sheath parameters is obtained.The results show that: under the plasma sheath cover,the antenna beam gain decreases and the antenna pattern is distorted.With the increase of electron density,the beam direction deviation becomes larger;and under the high electron density,the plasma sheath reflects the electromagnetic wave completely and the antenna pattern is reversed.3.In view of the influence of plasma sheath on the incoming signal,the electromagnetic model of the array receiving antenna is established,and the field intensity distribution at the element of the phased array receiving antenna under the plasma sheath is calculated,so as to construct the time-domain signal of the coupled plasma sheath and calculate the array guiding vector.Combined with music and unity Esprit DOA estimation algorithm,the influence of the target signal passing through the plasma sheath with different parameters on the incoming direction is analyzed.The results show that the DOA estimation error is small at low electron density,and increases significantly when the incident angle is greater than 60 °.At high electron density,the DOA estimation error is large and fluctuates,resulting in "black block" phenomenon.4.Based on the theory of least square method,the mathematical models of beam direction and DOA estimation deviation under different parameters of plasma sheath are established.Aiming at the problem of beam pointing deviation,a correction method based on echo estimation is proposed.According to the direction of the incoming signal,the beam synthesis of phased array antenna is corrected in real time,so that the main beam of the antenna is aligned with the target.Finally,the validity of the correction method is verified by simulation.In conclusion,the research results of this paper can provide data reference for the design of phased array antenna of reentry vehicle,and have important reference value for the analysis of the influence of plasma sheath on the active / passive direction finding of phased array radar on missile and the study of beam pointing error correction of antenna.