DOD's abhorrence of microwave tubes

by John Rhea

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WASHINGTON - The story of electronics in the second half of the 20th century has been the accelerating displacement of vacuum tubes by solid-state electronics. The result has been a peak improvement in the information processing power at the electronic component level by a factor of one billion, in the process creating entirely new technologies and new industries.

But, to recall Mark Twain's riposte, the report of the death of vacuum tubes is greatly exaggerated. Most of us stare into them during the day (computer monitors) and some of us at night (television sets). The long-heralded replacement of the venerable cathode-ray tube by an improved - and affordable - solid-state equivalent continues to recede beyond the horizon.

There's another category that vacuum tubes have staked out and in which they are embarked in a rear-guard action against the inroads of solid-state electronics: high-frequency applications spanning electronic warfare, satellite communications, and such specialized uses as high-energy physics research.

This is a market in free fall, and the amount of money available for basic research is plummeting accordingly. The Electronic Industries Alliance (EIA) is trying to alert the Defense Department to the necessity of shoring up this industry to support military-unique requirements. EIA officials estimate that domestic sales of microwave tubes - of which the Defense Department accounts for about 75 percent - declined from $588 million in 1987 and bottomed out at $234 million in 1996. Over the same period the number of major domestic manufacturers fell from 12 to six with a concomitant 50 percent reduction in employment, according to EIA.

The domestic industry regained some ground to about $280 million last year, with overseas suppliers accounting for another $140 million, says Jon Christensen, programs manager for business development at Hughes Electron Devices in Torrance, Calif., and EIA's point man in the effort to generate DOD support to preserve the industry. An estimated $100 million of the worldwide total is for traveling wave tubes (TWTs) for communications satellites, a market segment where such foreign firms as Thomson in France and NEC in Japan dominate.

Numbers like this rule out a commercial off-the-shelf, or COTS, approach, and EIA's Microwave Vacuum Electronics Division concedes as much in its plea to DOD. "COTS is not the solution," the organization maintains, "but DOD cannot avoid the responsibility to fund defense-unique R&D." Specifically, the proponents of vacuum tubes want research spending to support essential weapons systems requirements through 2003.

The group has a short list of weapons platforms dependent on microwave tube technology to serve as their eyes and ears: unmanned aerial vehicles, the Patriot missile upgrade, tactical missiles such as the advanced medium range air-to-air missile (AMRAAM), electronic warfare systems such as the ALQ-135, surveillance aircraft such as the Navy's E-2C and the Air Force's Airborne Warning and Control System (AWACS), and the Navy Ticonderoga-class (CG-47) Aegis cruiser.

Support for the technology base has been withering. The Defense Advanced Research Projects Agency pulled out in 1995, and the military services have shifted their funding to specific needs for platforms. The only DOD-wide focal point left is the Office of Naval Research (ONR), which has about $10 million a year available for work at the Naval Research Laboratory in Washington. ONR officials are reluctant to spend that much, according to Christensen, who estimates that even the shrunken industry is spending more on basic research than DOD.

EIA wants the DOD investment doubled to $20 million - half for ONR to sponsor exploratory development and the other half spread around the services for more advanced development projects. The money would go into addressing DOD's unique needs as measured in frequency (such as millimeter wave and extremely high frequency), power, bandwidth, and efficiency, particularly in the small quantities that rule out COTS.

Christensen estimates that more than 180,000 microwave vacuum electronic devices are currently deployed in some 270 fielded DOD systems. The Aegis cruiser alone has 8,000 devices per ship. Another major use is the missile seekers in the AMRAAM and Patriot and the kinetic kill vehicles for ballistic missile defense. Not all of these are easily replaceable with solid-state devices, which means the military services will have a continuing logistics support responsibility.

Nonetheless, there are some limited opportunities to spread the technology base over other than military users. In addition to the TWTs for military and commercial space applications, there is a potential for some overlap in klystron tubes. Department of Energy laboratories use very large, high-power, single-frequency klystrons in high-energy physics research while DOD uses smaller, less expensive, multi-frequency klystrons as the final amplifiers in many military radar systems. Another possible overlap is with airport and weather radars.

A compromise of a sort evolved over the past decade under tri-service sponsorship. This is the hybrid microwave power module, or MPM. An example is a medium-power C-band MPM for transceiver arrays developed by Northrop Grumman Electronics & Systems Integration Division in Rolling Meadows, Ill. Northrop Grumman engineers linked a solid-state driver with a vacuum tube output to double the power and double the efficiency at half the size and half the rated power of a comparable all-solid-state device. This pales in comparison to state-of-the-art advances in microprocessors and digital signal processors, but it shows that there are still some frontiers to pursue in vacuum electronics.

The industry base is modest at best. Six major suppliers remain. Three of them - CPI (formerly Varian Associates) in Palo Alto, Calif., and Beverly, Mass.; Hughes Electron Devices in Torrance, Calif.; and Litton Electron Tube Division in San Carlos, Calif., and Williamsport, Pa. - account for more than three-fourths of the total business. Three others, Northrop Grumman in Rolling Meadows; Teledyne Electronic Technologies of Rancho Cordova, Calif.; and Triton Electronics Technology Division in Easton, Pa.; concentrate on specialized applications. Two other companies, Econco in Grass Valley, Calif.; and California Tube Labs in Santa Cruz, Calif., provide services.

What the companies basically have to confront is a moving target, Christensen explains. At one time applications above frequencies of 10 GHz were naturals for high-power tubes. Then the threshold raised to 15 GHz. Today it is 20 GHz, he estimates. A new generation of weapons platforms may raise that threshold higher. The Air Force's F-22 jet fighter will use all-solid-state electronically scanned arrays. Such other new aircraft as the Navy's F/A-18E/F jet fighter-bomber and the future Joint Strike Fighter are also likely to use solid-state array radars.

Advances in gallium arsenide and silicon carbide for future solid-stage high-frequency components will also raise affordability issues for vacuum tubes. Realistically, the tube industry can't hope to win any of the sockets in future-generation systems, but it does have a continuing responsibility to support existing systems. That's why the companies want more research money from DOD, because they can't depend on COTS.

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August 2015
Volume 26, Issue 8

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