166 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 34, NO. 2, APRIL 2006 Experimental and Theoretical Results With Plasma Antennas Igor Alexeff, Fellow, IEEE, Ted Anderson, Sriram Parameswaran, Eric P. Pradeep, Student Member, IEEE, Jyothi Hulloli, and Prashant Hulloli Invited Paper Abstract—This report is a summary of an extensive research pro- gram on plasma antennas. We have found that plasma antennas are just as effective as metal antennas. In addition, they can transmit, receive, and reflect lower frequency signals while being transparent to higher frequency signals. When de-energized, they electrically disappear. Plasma noise does not appear to be a problem. Index Terms—Active antennas, antennas, plasma antennas, plasma devices. I. INTRODUCTORY SUMMARY W E have had the following experimental demonstrations of plasma antennas. Most of these demonstrations are documented on videotape, and are available on request. 1. Transmission and Reception: We have demonstrated transmission and reception of operating plasma antennas over a wide frequency range (500 MHz–20 GHz). The surprising results were that the efficiencies are compa- rable to a copper wire antenna of the same configuration, and the noise level seemed comparable with a wire an- tenna. The noise measurements will be repeated with a precision noise meter. 2. Stealth: When de-energized, the plasma antenna reverts to a dielectric tube which has a small radar scattering cross section. 3. Reconfigurability: At 3 GHz, we have demonstrated a parabolic plasma reflector. When energized, it reflects the radio signal. When de-energized, the radio signal passes freely through it. 4. Shielding: The plasma reflector, when placed over a re- ceiving horn and energized, prevents an unwanted 3-GHz signal from entering. When the antenna is de-energized, the signal passes through freely 5. Protection from electronic warfare: We have demon- strated that with a plasma reflector operating and re- flecting a signal at 3 GHz, a signal at 20 GHz freely Manuscript received August 31, 2005; revised January 24, 2006. I. Alexeff, E. P. Pradeep, and J. Hulloli are with the University of Tennessee, Knoxville, TN 37996 USA. T. Anderson is with Haleakala Research and Development, Inc., Brookfield, MA 01506 USA. S. Parameswaran is with Williams-Sonoma Inc., Memphis, TN 38118 USA. P. Hulloli is with Dell, Inc., West Chester, OH 45069 USA. Digital Object Identifier 10.1109/TPS.2006.872180 passes through the same reflector. The idea is that a plasma antenna can be so configured that a high-fre- quency, electronic-warfare signal can pass through the antenna without appreciable interaction, while the an- tenna is transmitting and receiving signals at a lower frequency. 6. Mechanical Robustness: We have developed two kinds of robust plasma antennas. In one design, the glass tubes comprising the plasma antenna are encapsulated in a di- electric block. In a second design, the plasma antennas are composed of flexible plastic tubes. We have found that the plasma does not damage the plastic tubes over periods of several hours if the plastic tubes are kept cool. Heat, not plasma, causes damage to plastic. 7. Mechanical Reconfigurability: We have been able me- chanically to manipulate the operating plasma antenna composed of flexible plastic tubes. In particular, we have designed a plasma antenna that may be compressed and stowed when not being used. 8. Plasma Waveguides: We have demonstrated a coaxial plasma waveguide. The advantage of such a waveguide is that it reverts to dielectric tubes when de-energized, and does not have large RADAR cross section. 9. Noise Reduction: We have found that plasma-generated noise is in general not a problem. However, to further improve the system, we have discovered several new methods of noise reduction. II. REVIEW OF PREVIOUS RESULTS The first phase of the plasma antenna project started with the idea of a coaxial plasma closing switch, shown in Fig. 1. In this switch, the outer conductor was a metal shell, and the inner conductor was a plasma discharge tube. When the tube was not energized, the outer shell comprised a metal wave- guide beyond cutoff, and no radiation was transmitted. When the plasma discharge tube was energized, the apparatus became a coaxial waveguide, and transmission of radio signals was ex- cellent. The work was done by W. L. Kang, as a thesis project, and was presented at a scientific meeting. The second phase of the research started when researchers at the Patriot Scientific Corporation, Carlsbad, CA, read of our work, and called me in as a consultant. They had an ongoing 0093-3813/$20.00 © 2006 IEEE