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Statement of

Dr. Ira W. Merritt
Chief, Concepts Identification and Applications Analysis Division
Advanced Technology
Directorate, Missile Defense and Space Technology Center
U. S. Army Space and Missile Defense Command

before the

Joint Economic Committee

United States Congress

Wednesday, February 25, 1998

"Proliferation and Significance of Radio Frequency Weapons Technology"

 

Introduction

      Thank you for your invitation and for this opportunity to offer testimony to the Joint Economic Committee regarding the proliferation of radio frequency (RF) weapons technology and its significance to the operability of our high value assets. I am employed by the U.S. Army Space and Missile Defense Command, but some of the opinions and conclusions expressed are based upon my own past experiences and observations and are not necessarily those of the Army.

      I am from the Advanced Technology Directorate (ATD) of the Missile Defense and Space Technology Center, U.S. Army Space and Missile Defense Command. One of our principal responsibilities is to develop innovative and advanced technologies for application to Army projects, joint missile defense projects and other programs of national importance. In particular, ATD evaluates the capabilities of technologies, including radio frequency weapon technologies, to establish their significance to the operability of our sophisticated electronics. Our interest in RF weapon technologies has increased in the last several years as a result of:

 

  Rapid advances in RF sources and antennas
  Increased interest by other countries, and groups, in RF weapons and RF mitigation
  Increased susceptibility to microwaves of miniature solid state electronics
  Insights from our travel to Russia and from ongoing technical exchanges with Former Soviet Union scientists and co-workers in United Kingdom, Sweden, and Australia.

      Our work with Russian scientists has been particularly useful in confirming that their approaches to technical problems are often very different from ours. Over the past several years we have visited laboratories developing directed energy weapon technologies, pulsed power systems, high power microwave technologies, high power lasers, and space-based neutral particle beams. In 1992, we visited the Moscow Radio Technical Institute, which was developing high-power microwave (HPM) sources and which had a large test facility for performing susceptibility and effects measurements. In 1994, we visited the Kharkov Physico-Technical Institute in Ukraine, where they were developing: high power microwave sources, such as the magnetically insulated linear oscillator (MILO); neutral particle beam sources; prime power systems; and where they were also performing susceptibility and effects tests. The MILO was invented in the U.S., but we discontinued work on it in the late 1980s. The Soviet Union (SU) picked up the technology and successfully continued its development. Russia also exploited the magnetocumulative generator (MCG) as an explosively driven power supply. The MCG was developed by Dr. Andrei Sakharov in the SU and the Russians have used MCG power supplies extensively to drive ultra wideband (UWB) and HPM sources, lasers, and railguns. In 1995 we visited: the Kurchatov Institute to discuss laser and high current problems, the All-Russian Electrotechnical Institute to discuss high voltage technology, Ioffe Physico-Technical Institute in St. Petersburg to discuss ultra fast switches, and the Institute of Problems of Electrophysics, also in St. Petersburg, to discuss pulse power and plasma technologies. My comments in the rest of this testimony are based upon the results of visits to Russian laboratories, visits to other countries, continued scientific contacts, research reports from contracts, some test results and open source literature.

 

Background

History: It has long been a concern in the scientific community that Soviet scientists led the world in development of RF weapon technologies. This concern was heightened in 1994 when Gen. Loborev, Director of the Central Institute of Physics and Technology in Moscow, distributed a landmark paper at the EUROEM Conference in Bordeaux, France. In this paper Dr. A. B. Prishchepenko, the Russian inventor of a family of compact explosive driven RF munitions, described how RF munitions might be used against a variety of targets including land mines, sea skimming missiles, and communications systems1, 2, 3. He further popularized these munitions with articles in Russian naval journals and in other professional journals and magazines4.

      The Soviet Union had a large and diverse RF weapons program and remnants of this work continue today within FSU countries. The scope and results of the Soviet program are poorly understood, but ATD personnel have been at the forefront of efforts to gather information and to understand it5 and its accomplishments through Windows on Science and contracts for R&D effort. Our principal objective is to understand requirements and to identify technologies applicable for RF mitigation. Nevertheless, large uncertainties still exist concerning the status of RF weapon development and associated efforts to mitigate their effects on electronics. In spite of these uncertainties, it is clear that many nations continue to aggressively pursue the development of RF weapons and techniques to mitigate their effects6.

Proliferation: Worldwide interest in RF weapons has increased dramatically in the last several years. The collapse of the Soviet Union is probably the most significant factor contributing to this increase in attention and concern about proliferation. A recent study of open source literature dealing with RF weapons6 clearly documented the worldwide interest in RF weapon technologies and my testimony is offered in the context of these conclusions. A few of the report's key judgments were that:

 

  1. ".construction of effective explosively-driven Flux Compression Generator devices is entirely feasible for established military powers such as Russia, China, France, Germany, et cetera,."
  2. "There is no confirmed evidence of employment of such a device to date . available in open sources".
  3. "Modern Metal Oxide Semiconductor technology, on which most of our critical national infrastructures depend, unless deliberately protected or "hardened", is extremely vulnerable to even low-power electromagnetic pulses..."
  4. ".it is well understood that the US is disproportionately more vulnerable to RF attack than are less developed nations."

      Specific examples of interest in RF weapons and the proliferation of this technology follow. The French Gramat Research Center has dedicated significant assets to study the effects of electromagnetic energy on electronics and in 1989 Thompson CSF published brochures in which they stated that they were developing RF weapons7. A 21 January, 1998 newspaper article in the Swedish newspaper SVESNSKA DAGBLADET8 reported that the Swedish National Defense Research Institute purchased a Russian "suitcase bomb" that uses high power microwaves to "knock out" computers and destroy all electronics within the radius of its "detonation". The article also reported that this device is being sold commercially and that it has been sold to the Australian military. The price was reported to be several hundred thousand Kroner, or about $100,000. Mr. Carlo Kopp, an Australian professor, who claims to have had a relationship with their military, has his own web site (http://www.cs.monash.edu.au/~carlo) and has provided detailed papers on the alleged effects of RF weapons and sketches of design concepts9. A simple search on the Internet recently identified 95 websites that referenced Mr. Kopp's work. These included 16 sites in the U.S. and 18 sites in other countries, not including Australia. The Internet is becoming a significant factor in enhancing the interest in RF weapons.

Waveforms and Susceptibility: State of the art semiconductors are becoming more vulnerable to the effects of radio frequency energy as semiconductor features become smaller and smaller10, 11, 12. Commercial microelectronics make heavy use of metal oxide semiconductor devices which fail when subjected to voltages that exceed the dielectric strength of the component or when the device melts as a result of heating from currents induced by the RF pulse.

      High-power microwave and ultra wideband signals differ in their pulse length and frequency content (Figure 1). HPM sources produce short, very high power, narrowband pulses, often billions of watts (gigawatts) in billionths of a second (nanoseconds). If HPM waveforms are in-band, they can efficiently couple energy into the target and energy is available to disrupt or to cause damage to sensitive "front door" components that are connected to antennas. However if the HPM frequency is not in-band, the energy must enter through a "back door" and coupling to the target is generally poor. In this case, much less energy enters the target to disrupt or to cause damage. UWB sources generate a much wider band of frequencies than do HPM sources, and thus ensure that some energy is at a frequency to efficiently couple to the target. However, since the energy is spread across a wider band, the power spectral density is lower and the amount of energy available in a waveband is also much lower. As a result, an UWB device is more likely to disrupt than to destroy a target, except at very close range. Many UWB sources can be repetitively pulsed and therefore can continue to disrupt the target as long as the source is functioning and within effective range. Many systems tend to be susceptible to disruption or damage at specific, sometimes unpredictable, frequencies. As a result, UWB weapons are well suited to exploit these susceptibilities, since they produce significant energy over a wide range of frequencies. This area has been aggressively researched by the Soviet Union, Russia, and others.

      Extensive work has been conducted to understand the effects of high-altitude nuclear EMP (HEMP) on systems and components, but these data are mostly for frequencies less than 1 GHz and for pulse widths in the range from 50 nsec to 1usec. The shorter pulses characteristic of HPM and UWB waveforms are significant because current methods for protecting electronics from HEMP, and other anticipated sources of disruption, will not be effective against pulses from RF weapons. High-altitude nuclear EMP does not have significant energy above a few tens of megahertz, whereas HPM spectra are typically in the few gigahertz to tens of gigahertz range and UWB spectra may contain energy in the frequency range from hundreds of megahertz to a few gigahertz. There is extensive information on the effects of lightning and nuclear EMP on electronic devices, but these pulses are significantly longer than the pulses from HPM and UWB sources. Since HPM and UWB pulses tend to be shorter than the response times of most limiters, their RF energy can pass largely unattenuated into the target and cause upset or damage before the limiter can turn on. Tests over the last 10 years have produced data on component responses to pulse widths in the range from 1 to 50 nsec. However little information is available that describes electronic responses for incident pulses having sub-nanosecond pulsewidths. Testing is needed to establish effects of the following general waveforms: very short (nanosecond and sub-nanosecond) single pulses, multiple closely-spaced very-short pulses, and long (millisecond) pulses.

      Much of the existing effects data is from direct drive tests. Such tests produce the most repeatable indication of whether or not the pulse in question will upset or damage the device being tested. However these tests do not help clarify the issue of whether or not the RF waveform in question will actually couple through the walls, openings, filters, cables, and wires that separate components at risk from the external environment. This uncertainty creates a situation in which even the best analysis must be based upon significant assumptions. As a result, our commercial and military systems may be much more, or much less, susceptible to upset or damage than we now assume. As a result, characterization of representative components and circuits and the effects of physical configurations are badly needed for very short pulses.

      A 1996 paper by Bludov, et al12 from the Kharkov Physico-Technical Institute, Ukraine described HPM and UWB testing on electronic components and biological systems. The paper identified three levels of damage: temporary upset, permanent upset, and burnout. It appears that Ukraine has a systematic program to characterize the effects of HPM and UWB waveforms on electronic components.

Example Weapon Related Technologies

      RF weapon-related sources can be classified in several ways, including: HPM or UWB, pulsed or continuous, single shot or repetitively pulsed, and very short pulse (nanosecond) or long pulse (microsecond to millisecond). In addition, the electrical or explosive power source has a significant effect on the output characteristics of the device. For example, the explosive driven munitions described by Mr. Carlo Kopp and the RF munitions described by Dr. Prishchepenko are single shot devices that convert the chemical energy of high explosives first into magnetic energy, then into electrical energy and finally into microwave energy. This multi-step conversion of energy is inherently inefficient, but explosives are very compact sources of energy, modern electronics are not very robust to external sources of energy, and the intent is to place the source/weapon as close to the target as possible. Electrically driven devices have fewer energy conversion steps, but typically they are larger and produce less power per pulse.

Electrically Driven Devices: The electrically driven (non-explosive) devices require an external power supply and energy storage system, which often leads to larger and less self-contained systems than can be produced by explosive-driven approaches. However, two recent technologies that minimize this limitation are the solid state pulsers developed at Ioffe Physico-Technical Institute in St. Petersburg and the RADAN system. These devices are quite compact and can be powered by small hand-carried energy sources.

      Pulsers developed at Ioffe Physico-Technical Institute are based upon very fast (nanosecond and picosecond) solid state "on" and "off" switches developed by Prof. Igor Grekhov and Dr. Alexi Kardo-Syssoev. These switches have recently been used to generate 10 nanosecond, 10 KHz pulses for a prototype ground penetrating sensor that is now being used commercially in St. Petersburg (Figure 2). This 10 kg portable sensor is said to be used routinely to image to depths of 200 meters with an accuracy of 1% of the depth and it is claimed to be able to image down to 1000 meters with slightly lower resolution13. Jammers based upon these switches can be made small enough to fit into a briefcase. A recent version is said to weigh 6.5 kg and to deliver fields of 30 kV per meter at 5 meters. This is comparable to high-altitude EMP (HEMP) field strength. An optimized version is said to deliver 100 kV per meter at 5 meters14, 15 and the pulse width and repetition rate can be tuned to have the maximum effect on the intended target.

      RADAN16 (Figure 3) is a compact high-current electron accelerator that is a little smaller than an attaché case and weighs about 8 kg with its rechargeable 12 volt battery power supply, but not including its antenna. RADAN can be used to stimulate several outputs including lasers, x-rays, wide band RF and high power microwaves that allow RADAN to be used as a jammer. RADAN output parameters are: total output power > 5 MW; repetition rate up to 1 kilohertz; pulse width about 2 nanoseconds; and output pulse bandwidth from 1 MHz to 5 GHz. A directional antenna has been developed and the developer has proposed that RADAN could be used to stop car engines and to destroy the electronic arming and firing circuits of bombs. Limited testing of RADAN has been conducted in the U.S. and it was found to affect calculators and electronic watches.

      The Russian built NAGIRA radar produces short powerful pulses with the following characteristics17: 10 GHz fixed frequency, 5 nanosecond pulse length, 300 MW peak power, 2 Joules per pulse, 150 Hz pulse repetition rate. NAGIRA was purchased by the UK Ministry of Defence and was delivered to Defence Research and Evaluation Agency (DERA) Frazer, near Portsmouth, in November 1995. Indications are that the UK will use NAGIRA to investigate detection of fast moving targets in sea clutter, to study electromagnetic-pulse penetration into equipment and to measure the effectiveness of front-end protection devices. During initial field trials near Nizhny Novgorod, Russia (Figure 4), NAGIRA was able to track a helicopter at more than 150 km range and at altitudes as low as 50 meters. We understand that because of electromagnetic interference (EMI) concerns, Russian helicopters were not allowed to operate within several miles of the radar when it was operating at full power.

Explosively Driven Devices: Compact explosive-driven radio frequency munitions (Figure 5) being developed by Russia have recently received a great deal of attention. These munitions are claimed to range in size from a hand grenade to a 155-mm artillery shell18 and the output may be either a HPM or an UWB pulse. Since these warheads are part of a projectile, they are intended to detonate very near their target, so fratricide is not a problem as it would be with HEMP.

      In June 1997, a U.S. measurements team led by the Advanced Technology Directorate participated in a joint series of measurements on radio frequency munitions (RFM) at a site near Nalchik, Russia5. The purpose of these tests was to verify Russian claims about the output of Dr. Prishchepenko's compact explosively-driven RFM. The test results left Russian claims unconfirmed, since most U.S. measurement equipment was not allowed by Russian authorities to reach the test site and since Dr. Prishchepenko's team claimed that the RFM that were tested radiated in a band that could not be measured with equipment at the site.

      ATD engineers continue to evaluate RF weapon technologies, to work closely with other countries, and to identify technologies that can be adopted for military applications and commercialization. We maintain relationships with other scientists through direct personal contact at conferences and site visits, through small research contracts, in collaboration with the U.S. Department of State on International Science and Technology Center (ISTC) and Science and Technology Center of the Ukraine (STCU) projects, and through the U.S. Air Force's Windows on Science Program. ATD has been extremely effective in identifying and executing joint projects, such as the joint radio frequency munitions test in Russia and briefings on the solid state pulsers developed at the Ioffe Institute in St. Petersburg. We are now working to bring the underground imaging sensor and its developers to the U.S. to test its ability to detect land mines. Solid state switches developed by the Ioffe Institute are now imported by a U.S. company that produces water purification equipment using Russian pulse power hardware. ATD has cooperated in hosting many scientists under the Windows on Science Program, including a scientist from Loughborough University in England, the only university that designs, tests, produces and markets inexpensive MCGs.

      Many source and antenna technologies can be used to produce devices with very different output characteristics. For example, Russia reports that its cylindrical shock wave source generates a single gigawatt pulse about a nanosecond long. However, susceptibility tests in the FSU and U.S. suggest that irradiating a target with a train of nanosecond pulses is more damaging than a single pulse, since multiple pulses lower the damage threshold of the target12. As a result, Russian emphasis has been on devices that produce a train of pulses. Some designs are said to generate 50 to 100 pulses, each about a nanosecond long, in a burst of pulses about 10 microseconds long18.

      The implications of this summary are that there is an increasing variety of equipment capable of generating very short RF pulses that are capable of disrupting sophisticated electronics. These pulses are not addressed by current design standards and will challenge existing front-end RF protection and other forms of EMI protection. New capabilities are needed to reject high-power, very-fast RF pulses and to minimize their effects on systems.

      We believe that common EMI and EMP mitigation techniques will not provide adequate protection against nanosecond and sub-nanosecond pulses from future radio frequency weapons, since active mitigation device response times are typically several nanoseconds to microseconds. Faster solid-state devices do not now have the high power capability needed to protect systems from RFW pulses.

RF RISK MANAGEMENT

      Several fundamental questions must be answered before we can adequately understand the potential risk that radio frequency weapons pose to our military forces and civilian infrastructure. These questions are:

 

"What are the current and expected capabilities of RF weapon technologies?" "What are the effects of these weapons on potential targets?" and "What is the likelihood that our systems will be exposed to RF weapons as a result of terrorism, conventional conflict, etc.?"

      As I have stated, Advanced Technology Directorate has initiated high payoff research and development efforts to understand RF weapons technologies and we have also begun to develop broadly applicable RF mitigation techniques that can ensure the operability of our high-value assets in the presence of stressing electronic warfare environments. Our emphasis is on development of near-term, low-cost capabilities that are applicable to a broad range of military and commercial-off-the-shelf (COTS) electronics and that are relatively insensitive to the details of RF weapon output. We are achieving success in this effort and believe that superior results can be obtained by selectively involving a relatively small number of highly innovative and skilled researchers and that this can be done without a great commitment of funds. For example, one of our recent $100,000 research efforts provided test results that demonstrated the ability of a low-temperature sinterable liquid to reduce external RF fields by many orders of magnitude over a frequency range from a few megahertz to a few gigahertz. This low-cost material has broad military and commercial applications. It will greatly enhance our ability to use COTS electronics on the digital battlefield and to protect key elements of the national infrastructure.

      In my opinion, a more comprehensive risk mitigation effort should include the following tasks:

 

  Characterize expected electromagnetic environments by analyzing and understanding rapidly advancing RF source and antenna technologies. A variety of RF sources have been identified that could be used in RF weapons and that produce environments that can challenge the operability of our systems. We should evaluate these technologies, assess their potential for weaponization, and provide information to guide hardening measures required to mitigate their effects. The results of this task should be:

 

  1. credible information on the output of electrically-driven and explosively-driven RF sources;
  2. much better understanding of the capability of the rest of the world to threaten the performance of our sophisticated electronic systems,
  3. much stronger technical basis on which to develop broadly effective and low-cost RF countermeasures.

 

  Conduct tests to determine the effects of short pulse RF waveforms on representative electronic components, subsystems and systems. This task should establish the effects of anticipated radio frequency weapon waveforms on representative circuits to provide a basis for development of mitigation techniques for COTS and military electronics. It should test representative electronic circuits to RF weapon-like waveforms in a laboratory environment to better predict the coupling of RF energy into targets and to measure the effects on targets. The targets characterized should consist of representative classes of COTS and military electronics, i.e. commercial Global Positioning System (GPS) receivers, radios, computers, satellite communication systems, components from tactical operations centers (TOCs), etc. This effort should leverage ongoing Defense Special Weapons Agency (DSWA) EMP and HPM mitigation activities, which address a part of this problem, and should jointly select synergistic items for testing. This will permit unique insights into the robustness of representative electronics to all types of RF disturbances. The target electronics should be tested in anechoic chambers available at several service facilities and should use appropriate RF sources to ensure repeatable waveforms at the appropriate power levels and with appropriate frequency content. The target electronics should be instrumented so that both the effects of the radiation and the method of coupling can be determined. These results will permit quantification of the specific performance/capability needed for each mitigation technique.

 

  Use the results of effects tests to develop front-end limiters and electromagnetic interference (EMI) shields. This task should develop and quantify mitigation capabilities and implementation guidelines for low-cost, low insertion loss, miniature plasma limiters and low-cost, very light-weight films, filters, and software algorithms to reduce internal and external electromagnetic interference produced by either local/friendly emissions or high power hostile emissions. Since RF warfare and EMI spectra cover such a broad range of frequencies and power levels, several mitigation techniques will be required.

 

  Traditional methods of EMI isolation often use metal enclosures to prevent unwanted radiation from entering the circuit. These shields provides effective protection, but they add weight and are not applicable to some newer systems that may use COTS with lightweight, nonmetallic enclosures that provide little or no EMI protection. Low-cost, light-weight RF isolation techniques are needed that can be cheaply applied to COTS and military equipment to significantly increase their ability to continuously operate on the electronic battlefield.

 

  Analyses are now being performed on miniature plasma limiter front-end protection devices that are compatible with solid state manufacturing processes. Analysis will confirm the feasibility of a low-loss miniature plasma limiter and its essential parameters such as threshold electric fields, gas breakdown and recombination times. This device is intended to be installed in front of sensitive antenna and receiver elements to protect them from damage or disruption by incident high power RF signals.
 

Conclusions

      We cannot now precisely quantify the risk presented by radio frequency weapons, but we know that the risk is growing. I believe that we can respond to this risk by developing near-term, low-cost, broadly-applicable mitigation techniques. These techniques can greatly reduce our susceptibility to radio frequency weapon environments and thereby reduce the risk to our technological superiority that is essential to our military and economic preeminence.

      I again thank the Committee for the opportunity to appear and to comment on the proliferation of radio frequency weapons and their significance to our critical infrastructures.


 

ACRONYMS

 
ATD Advanced Technology Directorate
CSWS Cylindrical Shock Wave Source
COTS Commercial Off-The-Shelf
DSWA Defense Special Weapons Agency
EMI Electromagnetic Interference
EMP Electromagnetic Pulse
FCC Federal Communication Commission
FSU Former Soviet Union
GHz Gigahertz
GPS Global Positioning System
GW Gigawatt
HEMP High Altitude EMP
HPM High Power Microwave
ISTC International Science and Technology Center
kV Kilovolt
MCG Magnetocumulative Generator
MHz Megahertz
MILO Magnetically Insulated Linear Oscillator
MW Megawatt
NNEMP Non-Nuclear EMP
RF Radio Frequency
RFM Radio Frequency Munition
STCU Science and Technology Center Ukraine
SU Soviet Union
TOC Tactical Operations Center
UWB Ultra Wide Band



 

References

1 Prishchepenko, A.B., V.K. Kiseljov, and I.S. Kudimov. "Radio Frequency Weapon at the Future Battlefield", Proceedings of the EUROEM Conference, Bordeaux, France, June 1994.

2 Prishchepenko, A.B. and V.P. Zhitnikov. "EM Weapon (EMW) in Air Defense or Some Aspects of Application of EM Radiation in the High-Frequency Band as a Striking Force",

3 Prishchepenko, A.B. and M.G. Akhmetov. "Radioelectronic Strikes in General Forces Operations (Combat)", Voyennaya Mysl', No. 2, March-April 1995, pp. 42-48.

4 Prishchepenko, A.B. "Electromagnetic Munitions", 96UM0427, Soldat Udachi, Moscow, No. 3, 1996, pp. 45-46.

5 Altgilbers, L.L., I. Merritt, M. Brown, J. Henderson, D. Holder, and Merriwhether. OCONUS Radio Frequency Munitions Test Report, ATD-98-001, 4 December 1998.

6 Linder, J.C., W.R. Graham, M.S. Hewitt, and T.J. Skucas. Radio Frequency, Electromagnetic Pulse, and High-Power Microwave Weapons, National Security Research, Contract No. N39986-97-M-7241, 18 August 1997.

7 Lucien, Vayssie, Communications and Public Relations Supervisor, Centre d'Etudes de Gramat, Gramat, France.

8 Stockholm Daily SVESNSKA DAGBLADET, 21 Jan 1998

9 Kopp, C. "The E-Bomb: A Weapon of Electrical Mass Destruction", http://www.infowar.com/mil_c4i/mil_c4i8.html-ssi.

10 Taylor, C.D. and D.V. Giri. High Power Microwave Systems and Effects, Taylor and Francis Pub., 1994.

11 Benford, J. and J. Swegle. High Power Microwaves, Artech House, 1992.

12 Bludov, S.B., N.P. Gadetskii, K.A. Kravtsov, Yu. F. Lonin, I.I. Magda, S.I. Naisteter, E.A. Prasol, Yu.V. Prokopenko, S.S. Pushkarev, Yu.V. Tkach, I.F. Kharchenko, and V.I. Chemakov. "Generation of High-Power Ultrashort Microwave Pulses and Their Effect on Electronic Devices", Plasma Physic Reports, Vol. 20, No. 8, 1994, pp. 643-647.

13 Personal Communication with Moose Hill Enterprises, 22 January 1998.

14 Grekhov, "Semiconductor Switches and Generators of Gigawatt-Range Micro- and Nanosecond Pulses", 14th IEEE International Pulse Power Conference, Baltimore, MD, June-July, 1997.

15 Kardo-Sysoev, A.F., S.V.Zazulin, V.M. Efanov, Y.S. Lilkov, and A.F. Kriklenko. "High Repetition Frequency Power Nanosecond Pulse Generation", 14th IEEE International Pulse Power Conference, Baltimore, MD, June-July, 1997.

16 Yalandin, M.I., G.T. Smirnov, V.G. Shpak, and S.A. Shunailov. "High-Power Repetitive Millimeter Range Back-Wave Oscillators with Nanosecond Relativistic Electron Beam", Proceedings of the 11th International Conference on High Power Particle Beams, Vol. 2, Prague, 1996, pp.388-391.

17 Bunkin, B.V., A.V. Gaponov-Grekhov, A.S. Eltchaninov, F.Ya. Zagulov, S.D. Korovin, G.A. Mesyats, M.L. Osipov, E.A. Otlivantchik, M.I. Petelin, A.M. Prokhorov, V.V. Rostov, A.P. Saraev, I.P. Sisakyan, A.V. Smorgonsky, and V.A. Suvorov. "Nanosecond Radar System Based on Repetitive Pulsed Relativistic BWO", Proceedings of the 9th International Conference on High-Power Particle Beams, Washington, DC, May 1992, pp. 195-202.

18 Prishchepenko, A.B. and V.P. Zhitnikov. "Microwave Ammunitions: SUMM CRIQUE", Proceedings of the AMREM Conference, Albuquerque, NM, May 1996, in publication.