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Abstract-The plasma sheath communication blackout issue for hypersonic or reentry vehicles is addressed from a channel characteristic perspective. Different from previous research, this paper emphasizes the importance of plasma sheath channel in the study of plasma communication blackout, and the discussion on transmission and phase shift characteristic of plasma sheath channel and their effect on communication performance was made with detail. A mathematical plasma sheath channel model is proposed and following the roadmap about how to obtain channel characteristic parameter is given. Flow field simulation of a blunt conical body physical was made, and the electron density and collision frequency profile got from flow field result under different incident angle at Mach 10-20 are presented thoroughly. The performance for QPSK based communication system under the established plasma channel is evaluated finally. It is indicated in our research that channel attenuation feature variation regularity is consistent with that of incident wave or Mach number, but the phase shift variation regularity with incident frequency or Mach number appears fall into chaos because of multiple 360 degree removal of original phase shift from communication view and complicated ratio relationships among incident wave, plasma frequency and collision frequency. Communication simulations result show that bit error rate agree with phase shift chaos well and phase shift exert large influence on present typical racking, telemetry, and command system. Some useful implications obtained from this study to improve communication performance include high frequency, high power and further rapid acquisition/tracing phase-locked loop compensating large phase shift.

In this paper, a mode-selectable synchronous buck DC-DC converter with high-efficiency and low-quiescent current is proposed, which is suitable especially for using as a Li-on battery charger. The high efficiency is obtained by applying dynamic power management technology under light-load, which makes some modules of the chip enter to sleep state and the quiescent current of the whole chip down to 45 µA. At the same time, power MOS (Metal-Oxide Semiconductor) devices are also shut down to decrease the dissipation of the system. A simple loop compensation method is also proposed, which can eliminate the influence brought by high equivalent resistance of output's capacitor on the stability of the system loop. The converter has been made with a 0.5 μm CMOS (Complementary Metal-Oxide-Semiconductor) process. Experimental results show that the peak efficiency is 94% at output current 100 mA when the supply voltage is 2.7 V. Moreover, the output voltage can recover within 14 μs at 400 mA load step.

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A plasma sheath generated around a hypersonic vehicle can be a serious obstacle to fixedfrequency communications, especially navigation systems. This paper studies the effects of a plasma sheath on a Beidou navigation circular microstrip patch antenna. The dynamic stratified medium model method, which is based on the gradient of electron density profile curve, is employed to model the nonuniform plasma sheath. Using the algorithm calculation of the time-domain finite integration, the navigation antenna radiation pattern property is obtained, along with the changes in the reflection coefficient and input impedance properties. Results show that antenna pattern distortion, resonant frequency shift, and impedance mismatch caused by plasma are proportional to the electron density. The process of reentry blackout is also reproduced from the perspective of the antenna performance degradation. The inductor L and capacitor C (LC tuning circuit) impedance mismatch compensation scheme proposed is demonstrated to be effective and it can decrease return loss by 19.4 dB under the most serious plasma environment, thus reducing signal reflection and enhancing navigation system performance.