Effect of plasma on the intrapulse distortion of linear frequency modulated pulse

Abstract

This study analyzes intrapulse nonuniform amplitude distortion of the LFM (linear frequency modulated) pulse propagating through a plasma by conducting theoretical analysis and experiments. The FDTD-IFFT method is proposed to calculate the propagation of the linear frequency modulated (LFM) signal in plasma, and the nonuniform pulse amplitude distortion is verified by a comparison of experimental and theoretical results. The plasma will cause amplitude distortion of the signal which is characterized by two metrics: (1) the pulse amplitude difference ΔG and (2) the pulse amplitude nonuniformity degree ψ values. The degree of nonuniform distortion is determined by the carrier frequency, the bandwidth, electron density, and the collision frequency. The results shows that when the carrier frequency is close to the cut-off frequency of electron density, ΔG and ψ reach positive peak values, the amplitude shows an increasing trend, and pulse amplitude nonuniformity distortion is most serious. Moreover, ΔG is negative when the cut-off frequency of electron density is far greater than the carrier frequency, and the collision frequency is high. The pulse amplitude shows a decreasing trend under this condition. The higher the electron density and the collision frequency, the larger the ψ value and the absolute value of negative ΔG and the more serious intrapulse nonuniform distortion. The intrapulse distortion will cause a signal to noise ratio variation in a pulse which will seriously affect the signal detection. The conclusions of this study are crucial for the application of electronic systems on vehicles under a plasma and for deepening the understanding of the effect of plasma on electromagnetic waves.