166 ieee transactions on plasma science, vol. 34, no. 2

166 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 34, NO. 2, APRIL 2006

Experimental and Theoretical Results WithPlasma 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 arejust as effective as metal antennas. In addition, they can transmit,receive, and reflect lower frequency signals while being transparentto higher frequency signals. When de-energized, they electricallydisappear. Plasma noise does not appear to be a problem.

Index Terms—Active antennas, antennas, plasma antennas,plasma devices.

I. INTRODUCTORY SUMMARY

WE have had the following experimental demonstrationsof plasma antennas. Most of these demonstrations are

documented on videotape, and are available on request.

1. Transmission and Reception: We have demonstratedtransmission and reception of operating plasma antennasover a wide frequency range (500 MHz–20 GHz). Thesurprising 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 aprecision noise meter.

2. Stealth: When de-energized, the plasma antenna revertsto a dielectric tube which has a small radar scattering crosssection.

3. Reconfigurability: At 3 GHz, we have demonstrated aparabolic plasma reflector. When energized, it reflects theradio signal. When de-energized, the radio signal passesfreely through it.

4. Shielding: The plasma reflector, when placed over a re-ceiving horn and energized, prevents an unwanted 3-GHzsignal 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 aplasma antenna can be so configured that a high-fre-quency, electronic-warfare signal can pass through theantenna without appreciable interaction, while the an-tenna is transmitting and receiving signals at a lowerfrequency.

6. Mechanical Robustness: We have developed two kindsof robust plasma antennas. In one design, the glass tubescomprising the plasma antenna are encapsulated in a di-electric block. In a second design, the plasma antennas arecomposed of flexible plastic tubes. We have found that theplasma does not damage the plastic tubes over periods ofseveral hours if the plastic tubes are kept cool. Heat, notplasma, causes damage to plastic.

7. Mechanical Reconfigurability: We have been able me-chanically to manipulate the operating plasma antennacomposed of flexible plastic tubes. In particular, we havedesigned a plasma antenna that may be compressed andstowed when not being used.

8. Plasma Waveguides: We have demonstrated a coaxialplasma waveguide. The advantage of such a waveguide isthat it reverts to dielectric tubes when de-energized, anddoes not have large RADAR cross section.

9. Noise Reduction: We have found that plasma-generatednoise is in general not a problem. However, to furtherimprove the system, we have discovered several newmethods of noise reduction.

II. REVIEW OF PREVIOUS RESULTS

The first phase of the plasma antenna project started with theidea of a coaxial plasma closing switch, shown in Fig. 1.

In this switch, the outer conductor was a metal shell, and theinner conductor was a plasma discharge tube. When the tubewas not energized, the outer shell comprised a metal wave-guide beyond cutoff, and no radiation was transmitted. Whenthe plasma discharge tube was energized, the apparatus becamea 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 researchersat the Patriot Scientific Corporation, Carlsbad, CA, read of ourwork, and called me in as a consultant. They had an ongoing

0093-3813/$20.00 © 2006 IEEE

ALEXEFF et al.: EXPERIMENTAL AND THEORETICAL RESULTS WITH PLASMA ANTENNAS 167

Fig. 1. Coaxial plasma on switch.

Fig. 2. Early plasma antenna.

plasma antenna project, in which they wanted to use the dis-appearing feature of the plasma antenna to prevent ringing onsignal turnoff. Their problem was poor plasma antenna trans-mission and reception. A version of the first plasma antennais shown in Fig. 2. My investigation showed that under theirconditions of operation, the plasma antenna’s resistance was amegohm, and so did not match the 300 resistance of space.The solution was to pulse the plasma antenna to higher currents,as the plasma discharge has a resistance that decreases with in-creasing current. Under the proper conditions, we found thatthe plasma antenna transmitted and absorbed radiation virtuallyidentically to a metal antenna. In addition, the plasma-generatednoise appeared to be rather low.

The third phase of research started at the University of Ten-nessee, Knoxville. The work was transferred to the ASI Tech-nology Corporation, Henderson, NV. At the University of Ten-nessee, we constructed the plasma antenna shown in Fig. 2, as

Fig. 3. Early plasma reflector.

Fig. 4. Plasma antenna.

well as the parabolic reflector shown in Fig. 3. With this appa-ratus, we demonstrated stealth, reconfigurability, and protectionfrom electronic warfare.

The fourth phase of research was done at the Malibu Re-search Corporation, an antenna design facility in Camarillo, CA.We felt that precision measurements were required in a properfacility. In Fig. 4, we show a plasma antenna installed in anelectrical anechoic chamber. Also shown is a metal antenna de-signed to be an identical twin to the plasma antenna. The mi-crowaves are generated by a line antenna, focused in one di-mension by the metal pillbox, and focused in the second dimen-sion by either the plasma antenna or a metal twin. The resultswere remarkably successful, as shown in Fig. 5. First, when theplasma antenna was on, the transmission efficiency was virtu-ally identical to the metal antenna. Second, the radiation patternwas also quite similar to the metal antenna. Third, the noise wasnot particularly worse for the plasma antenna over the metal an-tenna. However, when the plasma antenna was de-energized, the


Fig. 5. Radiation pattern.

Fig. 6. Embedded plasma antenna.

reflected signal dropped by over 20 dB! In other words, the re-flected signal dropped by over a factor of 100.

For stealth projects, the first metal reflector could be incasedinside the body of a structure. However, this project is really aproof-of-principle, rather than a deployable system.

III. OTHER PLASMA ANTENNA PROJECTS

One of the criticisms directed at the plasma antenna is that it isfragile. As a researcher from another company told us, he builta glass plasma antenna, but it was no good, because it brokewhen he installed it underneath an airplane. To make a robustplasma antenna, we imbedded one in an epoxy block, as shownin Fig. 6. This imbedded antenna transmits and receives quitewell, and has survived several years of hard treatment.

A second, antenna related, plasma application is a plasmawaveguide, as shown in Fig. 7. Here we have an inner con-ductor comprising one plasma tube surrounded by an outer shellof eight plasma tubes. When on, the structure transmits radia-tion almost as well as a coaxial cable, but when off, the trans-mitted signal decreases by over 100 dB—a factor of . Suchplasma waveguides could convey radiation to the antennas on

Fig. 7. Plasma waveguide.

the mast of a ship, yet become transparent to radiation whende-energized.

Radar signals would pass through a de-energized waveguiderather than be reflected. In fact, these waveguides could pass infront of operating antennas and be virtually invisible when off.

A third plasma antenna application is reconfigurability. Theeffects of a reconfigurable plasma filter are shown in Fig. 8.

In one oscilloscope trace, we observe several spectral linesemitted from an oscillator driven to a nonlinear limit. In thesecond oscilloscope trace, several of the higher-frequency lineshave been removed by the energizing of a plasma interferencefilter placed between the transmitter and receiver.

IV. RECENT RESULTS

We have made remarkable discovery in the operation ofplasma antennas (patents pending). In the past, our plasmatubes were ionized by direct current (dc). However, if thetubes are ionized by extremely short bursts of dc, we find thefollowing remarkable improvements. The plasma is producedin an extremely short time—2 s. However, the plasma persistsfor a much longer time—1/100 second. This is the reason whyfluorescent lamps can operate on 60 or 50 Hz electric power.Consequently, if the pulsing rate is increased to 1 kHz, thetubes are operating at essentially constant density. There arethree benefits to this new mode of operation.

First, the exciting current is on for only 2 s, while it is off for1 ms. Consequently, the discharge current is only on for 0.2% ofthe time, so current-driven instabilities are not present for mostof the time. However, the current-driven instabilities in generalhave proven to be not serious.

In general, operating the plasma tubes in the noncurrent-car-rying, afterglow state should produce considerably less noisethan in operating in the current-carrying state. The decrease inplasma noise is obvious, but detailed measurements have beendeferred till later in the program.

Second (this was unexpected), the plasma density producedby the pulsed-power technique is considerably higher than theplasma density produced by the same power supplied in thesteady-state. This observation produces two beneficial results.

We can operate at much higher plasma densities than beforein the steady-state without destroying the discharge tube elec-


Fig. 8. Plasma filter.

Fig. 9. Signals from the two transmitters.

trodes. Formerly, using commercial fluorescent tubes, we werelimited to steady-state operation below 800 MHz. Now we canoperate at several gigahertz. The upper frequency limit has notbeen explored.

We can operate at much higher plasma densities using loweraverage consumption. This results both in much lower powerconsumption and reduced heating of the antenna structure. Ournew results are shown in the following figures.

In Fig. 9, the lower trace shows signals from two transmittersat 1.7 GHz and 8 GHz passing through a de-energized plasmabarrier. The upper trace shows the 1.7-GHz signal being blockedby the energized plasma barrier while the 8-GHz signal is ableto pass through.

We note that the received signal with the plasma windowon shows considerably more noise than that with the plasmawindow off. Surprisingly, we found that this noise signal ap-parently is not present on the microwave signal, but primarilyis due to receiver pickup via the power line. Disconnecting thereceiving antenna from the panoramic receiver does not changethe observed noise level.

In Fig. 10, we show the present experimental apparatus. Twotransmitting antennas are used with a ring of fluorescent lamps.

Fig. 10. Experimental apparatus.

Fig. 11. Pulsing apparatus.

The two signals are received by a horn antenna outside the ringof fluorescent lamps.

Fig. 11 is a schematic of our pulsing apparatus. A 0–30 KVsupply is connected to a resistance-capacitance (RC) supplycomprising 1.5-M resistor feeding a nanofarad capacitor. Theresultant high voltage arc over a spark gap to provide pulsedcurrent to the fluorescent lamps—up to 12 wired in series. Wefind that when operating arc high pulsing frequencies—1 kHzup—the spark gap tends to go over to a steady-state arc. Toprevent the steady state arc, a small blower is placed on thespark gap to flush out the ionized air. In practice, this solutionworks very well. The Fig. 12 photograph shows the pulsingplasma tubes and the receiving horn.

In conclusion, our recent inclusion of a pulsed power supplyfor our plasma tubes provides reduced noise, higher steady-statedc plasma density, and reduced power consumption. There arepossibly minor problems because of a slight plasma density fluc-tuation during the pulsing cycle. These problems will be ad-dressed in future work.

V. PLASMA FREQUENCY SELECTIVE SURFACES

Anderson developed a theoretical model of a plasma fre-quency selective surfaces and Alexeff provided the experiment.This research is focused on using plasma as a substitute formetal in a frequency selective surface (FSS). FSS have beenused for filtering electromagnetic waves. Each FSS layer has tobe modeled using numerical methods and the layers are stackedin such a way to create the desired filtering. Genetic algorithms


Fig. 12. Pulsing plasma tubes and receiving horn 20.

Fig. 13. Comparison between theoretical and experimental results for afrequency selective surfaces.

are used to determine the stacking needed for the desiredfiltering. This is a complicated and numerically expensiveprocess. We developed a method to replace metal in a FSS withplasma elements. Our plasma FSS can be tuned to a desiredfiltering by varying the density in the plasma elements. Thiscould save much of the routine analysis involved in the standardanalysis of conventional FSS structures. The user simply tunesthe plasma to get the filtering desired. Plasma elements offer thepossibility of improved shielding along with reconfigurabilityand stealth. Plasma FSS can be made transparent by turning theplasma off. This extends our previous scientific achievementsin the development of the plasma antenna.

As the density of the plasma is increased, the plasma skindepth becomes smaller and smaller until the elements behaveas metallic elements and we create filtering similar to FSS withmetallic elements. Up until the metallic mode for the plasma,our theory and experiments showed that the plasma FSS had acontinuous change in filtering. We developed a basic mathemat-ical model for a plasma FSS by modeling the plasma elementsas half wavelength and full wavelength dipole elements in aperiodic array on a dielectric substrate. The theoretical modelwith numerical predictions predicted results in good agreementwith our experiments on the plasma FSS. Theoretically we used

Flouquets Theorem to connect the elements. We determinedthe transmission and reflection characteristics of the plasmaFSS as a function of plasma density. We utilized frequenciesfrom around 900 MHz to 12 GHz with a plasma frequencyaround 2 GHz. We pulsed plasma tubes to continuously varythe plasma density and observed the tunability of the reflectionand transmission of electromagnetic waves. As the plasmadensity decays, the amount of transmitted electromagneticenergy increased as expected. However, at electromagneticsignals at frequencies well above the plasma frequency, theplasma FSS was transparent. We also rotated the polarizationof the transmitting antenna by 90 and produced a similar butreduced effect.

We modeled an array of plasma frequency selective surfaces.Similarly, we made the plasma FSS in the laboratory. Ourtheory and experiment were in close agreement. A comparisonof the theoretical and experimental results is given in Fig. 13.One reason that the theoretical and experimental results are notcloser is that the theoretical results were for an infinite surfaceand the experimental results were for a finite structure. Theplasma FSS is unique and new to the field of electromagneticfiltering. Others have developed FSS filters using metal anddielectrics, but we are the first to use plasma and the reconfig-urability that it offers. The potential payoff for this technologyis high and the risk is moderate. It is moderate since we havedeveloped plasma antennas with transmitters, but the plasmaFSS is in some ways easier to develop since they do not requiretransmitters.

The plasma FSS can shield antennas, military electronics, andradar systems in a tunable way. If no shielding is needed, turningthe plasmas off causes the shield to be invisible. Plasma FSSallow users to filter out any undesirable radiation, but at thesame, time enabling operations outside that band. The poten-tial for technology transfer is significant since the plasma FSScan be tuned to filter out unwanted radiation from commercialproducts or tuned to filter electromagnetic emissions to meetFCC EMC requirements.

VI. ORGANIZATIONAL DETAILS

We have incorporated our company, Haleaka Research,Brookfield, MA, in which Anderson is President, and Alexeff isChief Scientist. The present work is being supported by SBIRand STTR grants from the U.S. Army, the U.S. Navy, and theU.S. Air Force. The experimental research is being carriedon in the Electrical Engineering Laboratory, the Universityof Tennessee. In addition, we have consulting work with theMalibu Research Corporation, Camarillo, CA.

The results of our work can be summarized as follows.

1) Concerning plasma antenna efficiency on transmissionand reception, the plasma antennas appear to work justas well as metal antennas as long as two criteria aremet. a) The plasma density is sufficiently high—theplasma frequency should be considerably above the radiofrequency being used. b) The coupling to the plasma isoptimized. The measurements confirming these state-ments were made at three separate locations by threedifferent, independent, groups. The first group was at


the Patriot Scientific Research Corporation, San Diego,CA; the second group was at the Electric Boat Corpora-tion, Groton, CT (U.S. submarines), and the third groupwas The Malibu Research Corporation, Calabasas, CA(antenna development). In the Groton experiments, theplasma antenna communicated between two computerstransmitting at 900 MHz. All experiments showed thatplasma antenna elements performed within a fewdB of a metal antenna. Recent results using plasmaantennas in the pulsed mode have transmission and re-ception taking place in noncurrent carrying plasma.

2) Concerning noise in plasma antennas, in the experimentslisted above, noise was never a problem. At most, noisewas a few decibels above the metal antenna, which wasalways used for reference. In the Groton experiments, theplasma antenna was compared to a metal antenna in anelectrical anechoic chamber. In the Malibu experiments,the plasma reflector also was compared to a metal reflectorin an anechoic chamber. In both cases, the noise level wasa few decibels above the metal antenna.

3) Concerning the plasma antenna igniting in a pulsed RFfield, the answer is most interesting. The plasma may ormay not ignite in an intense RF field, depending on thedesign of the plasma antenna!

4) Concerning the nonlinear effects of plasma antennas athigh-power, no nonlinear effects have been observed sofar, but the investigation is still ongoing.

VII. CONCLUSION

The plasma antenna appears to work well and is becomingthe object of study in several laboratories. Plasma antennas areuseful in applications for stealth, reconfigurability, and protec-tion against electronic warfare.

REFERENCES

[1] G. G. Borg, J. H. Harris, D. G. Miljak, and N. M. Martin, “The applica-tion of plasma columns to radio frequency antennas,” Appl. Phys. Lett.,vol. 74, pp. 3272–3274, 1999.

[2] G. G. Borg, J. H. Harris, D. G. Miljak, D. Andruyezik, and N. M. Martin,“Plasmas as radiating elements,” IEEE Trans. Plasma Sci., submitted forpublication.

[3] J. Rayner, A. Whichello, and A. Cheetham, “Physical characteristics of aplasma antenna,” presented at the 11th Int. Conf. Plasma Phys., Sydney,Australia, 2002.

[4] M. Hargreave, J. P. Rayner, A. D. Cheetham, G. N. French, and A. P.Whichello, “Coupling power and information to a plasma antenna,” pre-sented at the 11th Int. Conf. Plasma Phys., Sydney, Australia, 2002.

[5] A. Cheetham, J. Rayner, B. Gilbert, and G. French, “Software wave ex-citation for plasma antenna applications,” in Proc. 23rd AINSE Conf.Plasma Sci. Technol., Adelaide, Australia, 2000, pp. 17–19.

[6] M. Moisan, A. Shivarova, and A. W. Trivelpiece, Phys. Plasmas, vol.24, p. 1331, 1982.

[7] C. Balanis, Antenna Theory. New York: Wiley, 1997, pp. 165–173.[8] G. G. Borg, J. H. Harris, N. M. Martin, D. Thorncraft, R. Milliken, D. G.

Miljak, B. Kwan, T. Ng, and J. Kircher, “Plasmas as antennas: theory, ex-periments and applications,” Phys. Plasma, no. 5, pp. 2198–2202, May2000.

[9] I. Alexeff, “Plasma antennas,” presented at the SMi 8th Annu. Conf.Stealth, London, U.K., Mar. 15–16, 2004.

[10] , “Plasma antennas,” presented at the SMi 9th Annu. Conf. Stealth,Apr. 11–12, 2005.

[11] I. Alexeff et al., “Advances in plasma antenna design,” in IEEE Int. Conf.Plasma Sci., Monterey, CA, Jun. 20–23, 2005, p. 88.

[12] Kostrov, Pakhotin, and Smirnov et al., Sov. J. Plasma Phys, vol. 21, no.5, p. 435, 1995.

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Igor Alexeff (M’72–SM’76–F’81) received theB.S. degree in physics from Harvard University,Cambridge, MA, in physics in 1952, and the Ph.D.degree in nuclear physics from the University ofWisconsin, Madison, in 1959.

He is a Professor Emeritus with the Universityof Tennessee, Knoxville. He has been working inplasma and microwave engineering for over 50years. He has a patent on the Orbitron MicrowaveMaser that has operated up to one Terahertz (1/3mm). He is an author and co-editor of the book High

Power Microwave Sources (Norwood, MA: Artech House). He has over 100refereed publications and over 10 patents. He has spent considerable timerecently on plasma stealth antennas, and is listed on several patents issued tothe ASI Technology Corporation. He has worked at the Westinghouse ResearchLaboratory on nuclear submarines, at the Oak Ridge National Laboratoryin controlled thermonuclear fusion, and at the University of Tennessee inindustrial plasma engineering. He has worked overseas for extended periods inSwitzerland, Japan, India, South Africa, and Brazil.

Dr. Alexeff was a co-founder of the IEEE Nuclear and Plasma Sciences So-ciety. He was President of that society in 1999–2000. He is a Fellow of TheAmerican Physical Society. He also passed the Tennessee State License Exam,and is a registered professional engineer.

Ted Anderson received the Ph.D. degree in physics from New York Universityin 1986.

He is currently a Research Professor in the Department of Electrical and Com-puter Engineering, University of Tennessee, and CEO of Haleakala Researchand Development, Inc., Brookfield, MA. He has done research and publishedin the areas of the foundations of quantum mechanics, atomic physics, fluid dy-namics, plasma physics, and antenna physics. While working for the U.S. Navy,he invented ten patents on the plasma antenna. Since 1999, he has worked withProf. Alexeff on plasma antennas. Together, they have invented several patentson the plasma antenna and plasma waveguides, and they presented several pa-pers at various conferences, which include the IEEE and AIAA organizations.

Sriram Parameswaran received the B.S. degree inelectrical engineering from University of Madras,Chennai, India, the M.S. in electrical engineeringand the M.B.A. degree in logistics from the Univer-sity of Tennessee, Knoxville, under the guidance ofDr. I. Alexeff.

He worked under various projects, which includeplasma sterilization, ball lightning, and plasmaantennas. He is currently a Project Engineer withWilliams-Sonoma Inc., Memphis, TN.

Mr. Parameswaran received the IEEE Nuclear andPlasma Sciences Society graduate scholarship award for the year 2004.

Eric P. Pradeep (S’05) was born in Coimbatore,India. He received the B.S. degree in electricaland electronics engineering from the University ofMadras, Madras, India. He is currently workingtoward the M.S. degree at University of Tennessee,Knoxville.

He has been working for Dr. Alexeff as a Grad-uate Research Assistant in the Microwave and PlasmaLaboratory for about two years.


Jyothi Hulloli received the B.S. degree in electricalengineering from Karnataka University, Karnataka,India. She is currently working toward the MBA de-gree at the University of Tennessee, Knoxville.

After receiving the B.S. degree, she worked as aResearch Associate at one of the top engineering col-leges of India. She is currently working as a Gradu-ated Assistant with Dr. Alexeff to assist in developingbusiness plans for plasma devices.

Prashant Hulloli received the B.S. degree in me-chanical engineering from Karnataka University,Karnataka, India. After working for a year withleading automobile giant in India, he received theM.S. degree in industrial engineering from Univer-sity of Tennessee, Knoxville and the MBA degree insupply chain management and marketing from thesame university in 2005.

While working toward the MBA degree, heworked as Graduate Assistant with Dr. Alexeffto assist in developing business plans for plasma

devices. Currently, he is with Dell Inc., as Supply Chain Manager/Consultantat West Chester, OH facility.

166 ieee transactions on plasma science, vol. 34, no. 2

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