A plasma stealth antenna for the US Navy

Abstract

Energy loss from high-energy electrons that pass through a transmission window causes an increase in window temperature. A technique to cool transmission windows that utilizes water under high pressure flowing in capillary ducts is presented. A model for fluid flow in ducts quantifies fluid pressure, water temperature, convective rate, and vapor pressure as a function of distance into a capillary duct subject to uniform heating.The results quantify a design to prevent vapor formation in a capillary duct and provide a limit on net power dissipation. An example quantifies the design of a 5-cm-diameter window that would support 30 mA/cmz continuously at a beam energy of 500 keV.We have received a Phase 1 SBIR contract from the U. S. Navy to develop a plasma stealth antenna. The concept is to use plasma discharge tubes as antenna elements. When the tubes are energized, they become conductors and can transmit and receive radio signals. When they are de-energized, they revert to nonconducting elements (in present tests, glass tubes), and do not reflect probing radio signals. The reflection problem is most acute for probing signals near the resonant frequency of the antenna, which produces a large reflection cross section. A second feature of the plasma antenna, is that it can be reconfigured during operation, by selectively energizing only some of the elements. It can therefore be "steered" electronically. This cannot be done with metal conductor antennas. A third feature of the plasma antenna, is that it can be turned off rapidly, reducing ringing on . pulse transmission.Preliminary tests before receiving the SBIR successfully demonstrated both the operation of the antenna in transmission and reception, and the stealth features on a Navy test range in San Diego. The tubes used in that demonstration were modified neon sign discharge tubes filled with helium, neon, argon, and a neon-argon mixture. More detailed experiments are under way to explore such topics as optimizing the system with respect to antenna-feeder coupling, radiation-pattern peaking, and signal-to-noise ratio.The excitation of a static ( w = 0 ) magnetic field mode in a plasma has been theorized for close to 30 years, but has never been observed experimentally. This mode has also been referred to alternatively as the "picket fence" or "free streaming" mode, reflecting the fact that it is supported by steady state current loops with alternating sense of direction ( k * 0 ) in the plasma. We present PIC simulations and preliminary experimental results of work being done at USC and UCLA to measure the free streaming mode when a moving gaslplasma boundary (e.g., created by a short laser pulse) moves either through a static electric field (e.g., an electric wiggler) or an incident electromagnetic wave. Comparisons of the experimental and simulations results with analytical results are also presented.

Plasma-based Radar Cross Section Reduction

“…Plasma can be used for antenna surfaces to generate low-observability characteristics (Alexef et al 1998). The hollow glass tube filled with low-temperature plasma acts as a plasma-based antenna.…”

Characteristics of AC-biased Plasma Antenna and Plasma Antenna Excited by Surface Wave

“…Plasma antenna originates back from the eighties of 20th century, and various ingenious ways has been devised to achieve such purpose. Plasma can be generated by UV laser irradiation, or by laser initiated pre-ionization followed by high voltage breakdown to form the main conducting channel [4], or by simply using commercial fluorescence tube to serve as reflector [5,6], or by much more expensive electron beam [7][8][9]. There were also exotic methods like explosion generating plasma antenna for fusion research.…”

FDTD analysis of a plasma whip antenna

“…Factors of low weight, small size, and the ability to reconfigure during operation, combined with those advantages mentioned above, enable plasma antennas to find wide applications. Kang and Alexeff have demonstrated that it is feasible to construct an antenna with a glass tube filled by low-pressure gas, such as a fluorescent tube [1,2]. Preliminary tests have successfully demonstrated the operation of the plasma antenna with regard to both transmission and reception, and the stealth features have been observed on a navy test range in San Diego.…”

“…A large number of antenna configurations with flexible excitation arrangements and DR shapes has been reported with results of DRAs with high radiation efficiency, wide bandwidth, and flexible polarization adjustment [1,2].…”