Influence of Time-Varying Plasma Sheath on the Lock Condition of Phase-Locked Loop for TT&C Carrier Tracking System

Time-varying plasma sheath likely causes a parasitic phase modulation effect on communication signals. It is essential to understand the effect of plasma sheath on the tracking telemetry and command (TT&C) systems for blackout mitigation. This paper comprehensively investigates the impact of parasitic phase modulation effect on the TT&C tracking system of Ka band signals, especially single-frequency and phase-modulated signals. A fluctuant electron density model in the space-time domain is initially established. The phase noise caused by the time-varying plasma sheath is then obtained through wave impedance numerical calculation method. The effect of the time-varying plasma sheath with different fluctuant intensities on the carrier tracking performance is investigated and quantitatively analyzed by imposing phase noise on a phase-locked loop model. Simulation results show that a large fluctuant intensity corresponds to a great impact on the lockout threshold. A critical fluctuant intensity is observed in the three typical TT&C signals. The effect of the time-varying plasma sheath on phase-modulated signals is more severe than that on single-frequency signals. The maximum tolerable fluctuant intensities are 12%, 10%, and 6% for single-frequency signals, binary phase shift keying signals, and quadrature phase shift keying signals, respectively. With the critical fluctuant intensity, their lockout thresholds are increased to 0, 6, and 4 dB, respectively.