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The tri-service program.

The pivotal contributions of an embryonic microwave power tube capability to Allied success in World War II and the dramatic expansion of military electronics during the Korean conflict led to a veritable explosion in vacuum tube electronics R&D in the 1950s and early 1960s. By 1960, the annual DoD technology base investment had reached a level exceeding $70 M (1991 dollars), as shown in Figure 1. The return on investment, the successful insertion of an effective microwave power tube technology into a wide range of military systems and the establishment of an annual military market for microwave power tubes of approximately $400 M, has persisted for three decades, as shown in Figure 2.

However, the era of vigorous, intense military investment in vacuum tube electronics R&D came to an end in the early 1960s with a fundamental shift in emphasis from vacuum tubes to solid-state electronics. Rapid growth in the performance exhibited by then-new microwave solid-state devices along with a perceived maturity of microwave power tube technology convinced military decision-makers that long range military needs would be served best by solid-state RF sources. A decision was made to pursue solid-state source development with the explicit objective of replacing all microwave power tubes with more advanced solid-state devices. Consequently, the annual DoD investment in microwave power tube R&D was reduced to $24 M (1991 dollars) by 1967. Not unexpectedly, established university research programs collapsed. Much of the creative talent was driven from the field and many productive lines of scientific inquiry were terminated because of this rapid and substantial decline in DoD vacuum electronics funding. In retrospect, the 1950s and early 1960s wistfully have been called the golden age of vacuum electronics.

However, in stark contrast to the projections of 30 years ago, the microwave power tube remains the basic building block for the majority of active military electronic systems. For example, in the recently concluded Operation Desert Storm, over 90 percent of the military microwave transmitters used were based on microwave power tubes. In addition to high power across wide bandwidth, power tubes provide systems designers with the benefits of high efficiency, high gain, ease of thermal management and relatively long life. Major breakthroughs may substantially improve the performance of alternative source technologies, but it is apparent that the power tube will remain the coherent-radiation source of choice for the output stage of military electronic systems, as shown in Figure 3.

Although the growth rate in solid-state device performance had decreased by the early 1970s, that of vacuum electronics continued to grow, as shown in Figure 4, and demonstrates its potential to respond to the challenges posed by evolving threats. An indifference to maintaining the state-of-the-art technology base in vacuum tube electronics has blunted this essential industry's ability to respond to defense needs over the past 20 years. Following the initial damaging plunge in funding that occurred in the late 1960s, the annual DoD technology base investment in vacuum tube electronics declined well below the target threshold necessary for vitality to a minimum of $10 M (1992 dollars) in fiscal year 1988. Consequences of this passivity are now evident. Research scientists and engineers, the human resource base upon which future advances depend, have chosen alternate career paths.

Recent Actions

Looking to the future, acknowledging the unique niche of the microwave power tube in military systems and recognizing the precarious condition of the talent base, the advisory group on electron devices (AGED) convened a special technology area review (STAR) on microwave power tube R&D in October 1988. In its report, [1] AGED identified microwave power tubes as a critical national defense technology that needs expanded funding over a period sufficient to rejuvenate the technology infrastructure. AGED noted that the depth and vigor of the vacuum tube electronics technology base have een severely weakened by a long term decline of R&D investments and that the trend must be reversed through vigorous and sustained funding. the primary recommendation was to implement a unified program based on tri-Service needs to take advantage of existing technical opportunities. The level of investment should approximate that which resulted in the original successful introduction of power tube technology and, more recently, RF solid-state amplifier and oscillator technology into military systems. This level was in the range of $25 M to $30 M per year. Five high impact opportunities for focused investment and recommended sustained funding (for not less than 10 years) above the current Service investments for 6.2 and 6.3A programs were identified.

The DoD Response to the STAR

The DoD-wide response to the AGED STAR findings and recommendations was three-fold. DARPA/DSO implemented a vacuum electronics initiative ($3 M in fiscal year 1991) centered on the two high risk, high payoff investment areas recommended in the AGED report, namely, wideband RF amplifiers based on gated electron emitters, such as field-emitter arrays, and second-generation fast-wave amplifiers for mm-wave radar. By focusing on wideband RF amplifiers, DARPA is anticipating EW applications for RF vacuum microelectronics. Second generation fast-wave amplifiers utilize advances in second-generation gyroamplifier technology. Having recommended these thrusts to DARPA, NRL took the lead in the planning and initial implementation of these efforts.

An additional $15 M of fiscal year 1991 funding, mandated for microwave power tube R&D by Congress during its consideration of the fiscal year 1991 defense budget, was directed to DARPA/DSO ($5 M) and the Naval Research Laboratory ($10 M) for implementation of an expanded microwave power tube R&D program. The DARPA assets were used to fund a single-year expansion of the DARPA/DSO vacuum electronics initiative and to inaugurate, jointly with the tri-Service program, the initial year microwave power module development.

To maintain the tri-Service vacuum tube electronics program in the out-years, DoD decision PBD-208 recommended placement of additional funds (fiscal years 1992 through 1997) in program element 62234N, which supports Navy electron device technology, including vacuum tube electronics. In addition, the PE 62234N also serves as the framework for the tri-Service vacuum electronics program, which provides the technical thrust for the DARPA vacuum electronics initiative. This initiative targets the development of wideband RF sources based on high performance gated electron emitters and of second-generation fast-wave amplifiers for airborne mm-wave radar. These activities had been pursued, albeit at lower funding levels, under NRL's in-house R&D program for several years.

Scientific and Technological

Opportunities

The activity recommended by the AGED STAR ranges from the extension of existing technology to the establishment of new areas of technology. The AGED STAR report identified five areas of vacuum electronics R&D with high military pay-offs that have now been implemented by the tri-Service/DARPA steering committee into currently funded programs. These programs include the microwave power module program, the high performance mm-wave amplifier program, the MMACE program, design-for-low cost activities and vacuum micro-electronics.

The microwave power module program supports the development of a supercomponent that integrates a solid-state driver, a vacuum electronic power booster and power conditioning to support shared-aperture array applications at affordable costs. The technical options for microwave power generation in the frequency bands of interest are either solid-state devices, embodied in either discrete or MMIC devices, or vaccum electronic devices, mainly helix or coupled-cavity TWT format. Solid-state devices are equally diverse, but, in the broadest sense, the major changes that have driven the military microwave industry are based on a few devises, including the Gunn diode, the silicon mixer diode, the silicon bipolar transistor and the GaAs field effect transistor (FET). In addition, silicon, GaAs and InP discrete devices provide both two- and three-terminal sources of medium power in the frequency range from 1 to 100 GHz. Vacuum electronics technology embraces a wide range of devices, including the traditional multiterminal vacuum tubes, such as triodes, pentodes and beam power tubes, as well as many linear-beam and crossed-field devices, which employ either slow- or fast-wave structures, such as TWTs, klystrons, backward-wave amplifiers and oscillators, gyrotrons, free electron lasers and Cerenkov devices. Several salient differences between vacuum electronic and solid-state technology that led to the supercomponent concept are listed in Table 1.

By incorporating both solid-state and vacuum electronics technology into a single unit, the microwave power module (MPM) combines their advantages and minimizes their disadvantages. Proposed MPM designs will combine a low gain vacuum power booster and a high gain solid-state drive with the requisite integrated power conditioning in a small cross-section, efficient, low noise amplifying module.

[TABULAR DATA OMITTED]

The high performance mm-wave amplifier program targets high power capability for future systems at 94 and 140 GHz. Recent progress with the electron cycloton resonance maser (ECRM), the gyro-pentotron and the free electron maser (FEM) has demonstrated the advantages of fast-wave devices in producing high power at high frequency. Slow-wave structures also are being investigated to develop the next generation of devices for radar and electronic countermeasures.

The advanced computational techniques program, known as microwave and millimeter-wave advanced computational environment (MMACE), encompasses both computer-aided design and computer-aided manufacture. The objective is to support the rapid design of vacuum electronic devices without the expense of traditional hardware R&D and to transfer the required manufacturing information in digital format as the device moves through to production.

The design-for-low-cost techniques will become mandatory design elements in the manufacturing of tubes. But initially, the tri-Service vacuum electronics program will emphasize the problems of cost, reliability and performance across Service applications. Service-specific needs to be addressed by this effort are, in the Army, TWTs for helicopter-borne, high power standoff jammers, such as the advanced tactical radar jammer; in the Navy, high duty CFAs for AN/SPY-1 upgrades; and, in the Air Force, TWT reliability for AN/ALQ-131 and 135 jammers used in F15 and F16 EW pods. This effort emphasizes the use of modern computational design techniques and provides a mechanism for instituting in industry the new design capabilities developed under the MMACE program.

Vacuum microelectronics combines the potential of solid-state micro-fabrication techniques with the power handling capabilities of electron transport in vacuum. This program will look toward developing a new class of gated-electron emitter power tubes with enhanced efficiency, improved power-bandwidth capabilities and increased compactness. Although TWT amplifiers can provide high power with good efficiency, they require focusing magnetic fields and high voltages, thereby increasing the weight.

The Roles of Industry, Academia

and Government

The strength of any technology base lies in the quality and ready supply of its scientists, engineers and technicians engaged in research and development. The serious decline in the scientific/engineering staff in the microwave power tube industry over the last two decades illustrates the current plight and the need for immediate DoD action. The talent base is now very low because of the scarcity of new talent, the loss of productive engineering staff and the age distribution of industry engineers and scientists, many of whom are retired or are nearing retirement.

The long term stability and effectiveness of a technology base requires all segments of the community, industry, academia and government, to be viable. Each sector plays a crucial role in military R & D and none can replace another. Each has a primary role in the technology base and a degree of overlap is required if interaction is to be effective. The situation in the microwave power tube industry provides an excellent example of this interaction and the penalties to be paid for prolonged imbalance. Recent actions to redress this concern required the catalytic actions of a government laboratory. Acting in response to the long range perspective of Service needs, the Navy, through NRL, cultivated an aggressive and effective R&D group in vacuum electronics.

Tri-Service/DARPA Vacuum

Electronics Program Start

The first phase of the overall tri-Service/DARPA vacuum electronics program was implemented in 1991. Four broad agency announcements were issued covering different program areas, resulting in the submission of 177 white papers and proposals. Of these, 40 new starts were funded using the newly available funding. The distribution of funds consisted of 46 percent going directly to the power tube industry, 21 percent to other industrial contracts (several of which fielded teams that included power tube companies), 13 percent to research centers (mainly not-for-profit organizations), 9 percent to the university sector and 7 percent to government laboratories as performers. Less than 5 percent of the total $17.833 M fiscal year 1991 plus-up was directed to support management activities and efforts within the cognizant government agencies.

It is clear that the programmed funds for the next four years of the program will be unable to support all contractors at their proposed expenditure rates. But many of the contractual thrusts launched in 1991 will move from an initial, conceptual phase of investigation into a more system-oriented phase, with different programmatic thrusts moving at different paces. As contractors move into the second phase of their investigation and their expenditures escalate, it will be necessary to reduce the number of contractors in order to stay within the programmed funding constraints.

Under circumstances such as these, management of the multicontractor distributed-Service tri-Service/DARPA vacuum electronics program becomes a critical ingredient for success. To ensure the success of the program, the tri-Service DARPA Steering Group will exercise the key role in developing and coordinating a DoD-wide vacuum electronics investment strategy. Semi-annual program reviews will be instituted to monitor progress across the full range of activities. Additional programmatic thrusts may be initiated in the future, but details will depend on the status of funding directed by DoD and the Services into the newly reinvigorated field of vacuum electronics.

References

[1] "Microwave Power Tubes: A National Security Concern," July 1990.

Robert K. Parker received his BS degree in physics from Allegheny College in 1964, his MS in space physics engineering from the Air Force Institute of Technology in 1966 and his PhD in nuclear engineering (plasma physics) from the University of New Mexico in 1973. From 1964 to 1972, he served in the US Air Force as a scientific project officer with assignments at the Air Force Institute of Technology, the Air Force Weapons Laboratory, the University of New Mexico and the Defense Nuclear Agency. Since 1972, Parfker has worked at the naval Research Laboratory in Washington, DC, where he has been actively involved in a continuing study of the science and technology associated with the generation of coherent radiation in non-neutral plasmas. Currently, Parker is the head of the Vacuum Electronics Branch in the electronic Science and Technology Division at NRL. He also is the administgrator for the Navy exploratory development project in vacuum electronics and is chairman of the Tri-Service/DARPA Vacuum Electronics Steering Group. He also serves as the Navy member on the DoD Advisory Group on Electron Devices and as a member of the Executive Board of the Air Force Advanced Thermionics Research Initiative program at the University of California, Los Angeles. He is a member of the IEEE, having served on the Executive Committee of the Nuclear and Plasma Science Society, Plasma Science and Applications Committee and Associate Editor of the IEEE Transactions on Electron Devices. Parker is also a member of the Plasma Physics Division of the American Physical Society, and Sigma Xi.

Richard H. Abrams, Jr. received his SB degree in electrical engineering from MIT in 1959 and his PhD degree in plasma physics from the University of Maryland in 1970. His industrial experience includes thermionic energy conversion research at ThermoElectron Engineering Corp. and General Motors Research Laboratory. He has been active in the energy and environmental policy area, and has consulted to both government and corporate management on strategic technical planning. Prior to joining the Naval Research Laboratory, he served as chief scientist of B-K Technologies, where he directed assessments of various critical technologies, including high power microwaves. Currently, he is head of the Sources and Fabrication Section, Vacuum Electronics Branch, in NRL's Electronics Science and Technology Division, where he is responsible for the direction of Navy research programs in vacuum microelectronics, secondary electron emitters, and thermionic emitters. Abrams is a member of the American Physical Society and Sigma Xi.
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Title Annotation:Special Report; The Navy's Role in the Vacuum Tube Electronics Program, Part 1
Author:Parker, Robert K.; Abrams, Richard H.
Publication:Microwave Journal
Date:Mar 1, 1992
Words:2670
Previous Article:The merging of photonic and microwave technologies.
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