Abstract
The effects of time-varying plasma on the propagation of a linear frequency modulated (LFM) pulse are investigated. An experiment on the propagation of LFM pulse in continuous time-varying plasma is described and a spectrum broadening phenomenon is observed. The phenomenon is due to intra-pulse amplitude and phase modulation of the LFM pulse by time-varying plasma; this explanation is verified by a comparison of the results of the experiment and theoretical analysis. The theoretical result is obtained by measuring the time-varying electron density that the intra-pulse modulation depends on and applying the measured time-varying electron density into calculation method presented in this paper. The effects of the bandwidth of the LFM pulse and oscillation frequency of electron density on the intra-pulse modulation phenomenon are then explored by another two experiments. Time-frequency analysis employing a smooth pseudo Wigner–Ville distribution (SPWD) is adopted to further analyze the phenomenon and results of time-frequency analysis confirm the earlier theoretical analysis and conclusions. The effect of intra-pulse modulation on the LFM pulse due to time-varying plasma should be emphasized in the application of the radar and communication systems on a vehicle under a plasma sheath.
Highlights
INTRODUCTIONVehicles are traveling at increasingly high speeds as advances are being made in aerospace engineering. The air becomes ionized and a plasma sheath forms around a hypersonic vehicle traveling at a sufficiently high speed owing to the high temperature and pressure generated. Since 1960, many studies have investigated the plasma sheath by considering the plasma sheath as a static dielectric. owing to the disturbance effect of the hypersonic fluid, the plasma sheath varies in time and the propagation of electromagnetic waves is complex. The linear frequency modulated (LFM) pulse is an important signal form widely used in radar and communication systems yet the propagation of the LFM pulse in time-varying plasma has rarely been investigated
The present paper investigates intra-pulse modulation of the linear frequency modulated (LFM) pulse due to time-varying plasma in simulation and experiment, which will benefit the application of the radar and communication systems on a vehicle under a plasma sheath
An experiment was conducted to explore the interaction between the LFM pulse and time-varying plasma; a schematic diagram of the experiment is shown in Fig. 1 and the photo of dynamic plasma generator is shown in Fig. 2.20 The plasma generator used in the experiment was an amplitude modulated radio frequency plasma generator and the plasma chamber had a diameter of 400 mm and length of 240 mm
Summary
Vehicles are traveling at increasingly high speeds as advances are being made in aerospace engineering. The air becomes ionized and a plasma sheath forms around a hypersonic vehicle traveling at a sufficiently high speed owing to the high temperature and pressure generated. Since 1960, many studies have investigated the plasma sheath by considering the plasma sheath as a static dielectric. owing to the disturbance effect of the hypersonic fluid, the plasma sheath varies in time and the propagation of electromagnetic waves is complex. The linear frequency modulated (LFM) pulse is an important signal form widely used in radar and communication systems yet the propagation of the LFM pulse in time-varying plasma has rarely been investigated. The linear frequency modulated (LFM) pulse is an important signal form widely used in radar and communication systems yet the propagation of the LFM pulse in time-varying plasma has rarely been investigated. Many studies have investigated time-varying plasma and analyzed its effect on the electromagnetic wave and signals. The LFM pulse signal is a commonly used signal in the field of radar and communication, and it is necessary to analyze the effect of time-varying plasma on the LFM signal from the viewpoints of theory and experiment. The present paper investigates intra-pulse modulation of the LFM pulse due to time-varying plasma in simulation and experiment, which will benefit the application of the radar and communication systems on a vehicle under a plasma sheath.
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