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As a vehicle reenters the atmosphere or travels at hypersonic speeds within it, a bow shock forms around the leading edge of the vehicle. The air is superheated as it passes through the shock wave and becomes ionized. This plasma layer prevents the transmission of radio frequency communications to or from the vehicle, causing what is know as communications blackout. In this paper, we present results from experiments performed to evaluate the use of crossed electric and magnetic fields to lower the plasma density in a region surrounding an antenna. Plasma number density, plasma frequency, and signal attenuation measurements were made with a Langmuir probe, hairpin resonance probe, and S2-1 probe, respectively. The hairpin resonance probe and the S2-1 probe measured frequency responses for input frequencies ranging from 200 up to 4000 MHz. Results show that this approach is a viablemethod for communications blackout amelioration.We found that the plasma number density decreases by as much as 70%with the operating conditions used in this work, and the plasma frequency dropped by asmuch as 75%. The increased reduction in the plasma frequency, as compared to the plasmanumber density, was due to the addition of greater magnetic field strength when the frequency measurements were made. In addition, frequencies that were previously attenuated by more than 10 dB have almost no attenuation after the application of the electric and magnetic fields.

Experimental Results for Communications Blackout Amelioration Using Crossed Electric and Magnetic Fields