Effect Of Plasma Sheath On Measurement And Control Navigation Antenna Performation

During the process of reentry, the aircraft is covered by a layer of plasma sheathdue to the interaction with the surrounding air. This layer of sheath not only reflects andabsorbs the electromagnetic wave but also affects the near-field distribution of antenna,which finally results in antenna impedance mismatch and radiation pattern distortion,and makes precise navigation impossible during the process of reentry. At present, theresearch on plasma-covered navigation antenna characteristics in our country, is still atthe preliminary stage and needs to be further improved.Devoted to the studies of navigation-frequency electromagnetic wave propagationproperty together with measurement and control navigation antenna performance underplasma sheath, this paper comprehensively analyses the effect of plasma sheath onmeasurement and control navigation antenna performance. In the study ofelectromagnetic wave propagation in plasma, the method of equivalent wave impedanceis applied to similarly calculate electromagnetic wave power reflection coefficient andtransmission coefficient with different electron density, collision frequency and incidentangles. In the study of plasma-covered measurement and control navigation antenna, thepaper employs the time-domain FIT (Finite Integration Technique), and similarlycalculates the characteristics of navigation antenna covered by uniform and non-uniformplasma. And then draws out the changing cures of the antenna impedance, frequencydeviation and radiation characteristics in different conditions of electron density andcollision frequency.Based on the two above studies, it is concluded that when plasma collisionfrequency is lower than the antenna communication frequency and the plasmafrequency is higher than the antenna communication frequency, the electromagneticwave and the antenna performance are apparently affected, which finally leads to thefailure of the antenna; and that when plasma collision frequency is higher than theantenna communication frequency and the plasma frequency lower than the antennacommunication frequency, the antenna performance is improved and can still workproperly.