By Edward J. Walsh
WASHINGTON — Military electronics research spending has been drying up over the last decade, which endangers the ability to produce high-performance RF components for the latest sensors, communications, and electronic warfare systems, Navy researchers warn.
The U.S. Naval Research Laboratory (NRL) in Washington released a long-awaited, hard-hitting study that reports on critical needs for vacuum and solid-state devices for defense systems and proposes a strategy for funding future work in advanced electronics technology.
The study of defense requirements for vacuum electronics and solid-state electronics technology, released in mid-August, calls for a balanced focus on development in vacuum-tube and solid-state electronics with new and increased investment. Without new research spending, NRL scientists warn, U.S. radar, communications, and electronic warfare technology may start falling behind.
The study reports that funding for advanced electronics — especially for vacuum electronics components necessary for high-power amplifiers — has declined precipitously since the early 1990s. It warns that the continued downward trend in funding endangers the services' ability to produce the high-performance devices required for advanced sensors, communications, electronic warfare, and other RF systems.
The study is from panels of senior research and development managers of all the U.S. military services. It responds to concerns about the decline in funding for defense electronics raised by the U.S. Department of Defense (DOD) 1999 Technical Area Review and Assessment for Electronics.
According to the study, funding for vacuum-electronics technology fell from about $19 million (constant dollars) in 1986 to $12.6 million in 1988. Funding then increased dramatically to a high of $35 million in 1993, but has since declined to $10 million for 1999, and is projected at $7.7 million in 2001.
Navy officials point out the funding decline threatens the industrial base for vacuum devices. Only a few companies — Litton (now Northrop Grumman) Electron Devices in Williamsport, Pa.; Communications & Power Industries (CPI) Inc. of Palo Alto, Calif.; Boeing Electron Dynamic Devices in Torrance, Calif.; and Teledyne Electronic Technologies in Los Angeles are considered primary sources for vacuum electronics.
The 2000 congressional defense authorization bill told the Navy to assess the DOD's technological and monetary needs for advanced electronics — particularly for vacuum and solid-state electronics.
The study, led by the NRL's Electronics Science & Technology Division, responds to direction to the NRL and the Office of Naval Researche's (ONR) Electronics division by former Chief of Naval Research Rear Adm. Paul Gaffney.
The study calls for $12 million annually for applied research in vacuum electronics — the same as was available in 1998. This money would pay for work on multiple-beam klystrons, gyro-amplifiers, highly linear traveling wave tubes (TWTs), and other vacuum-based devices.
It endorses a combined tri-service initiative, funded at $50 million annually, for rapid development of wideband gap semiconductor device technology, and support in the range of $5 million per year for producibility upgrades for gallium arsenide millimeter wave/microwave integrated circuit (MMIC) technology for high-power radar, telecommunications, and missile seekers.
The study also reveals a clear divergence of views on the direction of future technology development between the NRL, the DOD's Executive Agent for vacuum technology, and the Office of Naval Research, which provides the funding for Navy S&T.
NRL and ONR officials say the services need vacuum and solid-state electronic technologies. The study urges the DOD to provide "application-specific advanced technology development funding for power-amplifier component development, including a five-year tri-service program for vacuum electronics funded at $10 million annually."
The Office of Naval Research, however, added a caveat that stipulates that it "does not agree with this recommendation but believes that such a program should support the 'best technology (vacuum or solid-state).'"
Finally, the study calls for investment of $5 million for an applied research program in wideband gap semiconductors to pursue promising technology opportunities.
NRL's role as the DOD's executive agent for vacuum technology programs dates from its work in Project Reliance, established in 1991 to coordinate joint-service investment and research in vacuum electronics, This is according to Gerald Borsuk, superintendent of NRL's Electronics Science & Technology group, who oversaw the study.
Borsuk says that the NRL carries out extensive basic research in power electronics, electro-optics, nanoelectronics, and plasma science — in addition to its leading role in developing vacuum and solid-state technology.
Borsuk's group also collaborates with other NRL directorates to develop technology for specific systems. The NRL's Vacuum Electronics and Solid-State branches teamed to develop microwave power modules (MPMs) — hybrid devices that incorporate a vacuum electronics power booster with a solid-state driver. MPMs now are being fielded to Navy RF systems.
There is an "appropriate dynamic" between military uses of vacuum electronics and solid-state, says Bob Parker, director of the NRL's Vacuum Electronics branch. Vacuum technology remains the dominant technology for high-power military transmitters in fielded systems, even though military applications that require lower power per radiating element have shifted from vacuum to solid state, he points out.
Parker says it is essential to "overlay the capabilities of both vacuum and solid state against particular system requirements. The designer has the advantage of being able to look at system architectures that could be derived from either vacuum or solid state."
The NRL-led study of investment strategies points out that vacuum-based power amplifiers offer advantages in efficient power and bandwidth over solid-state devices. Solid-state amplifiers generally provide advantages in packaging and reliability. NRL and ONR officials say that vacuum devices currently still enjoy a cost advantage over solid state.
The study, which focuses primarily on high-power amplifiers, covers service requirements for airborne, shipboard, and ground systems, including radars, electronic warfare, communications, and multi-functional systems. These will include the Navy's advanced multi-function radar and the Army's multi-mode radar and are intended to be capable of transmitting multiple simultaneous sensor, communication, and electronic warfare beams.
The study points out that military radars currently in service almost exclusively use vacuum-electronics amplifiers, primarily TWTs, because of their requirements for high power, even while they rely on solid-state devices for receive functions.
The U.S. Air Force's F-22 fighter and the Navy's F/A-18E/F fighter-bomber aircraft are programmed for X-band solid-state radars, based on current-technology gallium arsenide. Other promising solid-state technologies include indium phosphide and wideband gap semiconductors. The Air Force's Predator unmanned aerial vehicle uses hybrid MPMs for its Ku-band synthetic aperture radar.
Among shipboard systems, the Navy's theater ballistic missile defense radar, the multi-function radar, and volume search radar, also are being developed with solid-state technology. The study points out that vacuum-based multiple-beam amplifier technology could help upgrade the SPY-1 phased-array radar aboard Navy Ticonderoga-class cruisers and Arleigh Burke-class destroyers.
Among ground-based systems, the Marine Corps multi-role radar is to be a fully solid-state system, as is the radar for the Army's theater high-altitude area defense system.
Solid-state technology, the study says, is highly desirable for missile seeker phased-array antennas because of the need for small size. Electronic warfare jammers currently require the high-power performance of vacuum amplifiers.
The study says however that future electronic warfare systems may introduce two-dimensional electronically steered beams that could incorporate wideband gap devices. The Navy's advanced integrated electronic warfare system (AIEWS, increment 2) will use planar active arrays supported by solid-state devices.
For other current applications, TWTs are used for wideband jamming in 100-watt continuous wave and one-to-two-kilowatt pulsed range. The study suggests that microwave power modules and millimeter wave power modules could provide the required transmit capability.
Borsuk says that contrary to the wide perception of vacuum electronics as a mature technology, the NRL is pursuing innovative research in vacuum devices. The NRL-led study points out "dramatic advances in vacuum-device performance have been achieved during the last decade."
Navy scientists in recent years have built on 1960s research to introduce helix and coupled-cavity TWTs, klystrons, magnetrons, and crossed-field amplifiers. The hybrid vacuum-solid-state MPMs combine the power, efficiency, and bandwidth advantages of a vacuum amplifier with the low-noise performance of a solid-state amplifier.
Parker points out also that despite the popular notion of vacuum electronics as bulky glass tubes, current TWT amplifiers remain critical elements in the transmitters of state-of-the-art commercial telecommunications systems, including satellite communications. Rapidly increasing bandwidth and high-data-rate requirements to support the service's visions of network-centric warfare underline the need for continued work on TWTs and other vacuum devices for power amplifiers, the study states.
Vacuum technology will not be replaced by solid-state any time soon, Navy officials say. Officials of the Naval Surface Warfare Center's division in Crane, Ind., recently estimated that the number of vacuum tubes in shipboard systems would continue to increase through 2015.
