The key to stronger communications? Vacuum tubes.

Traveling wave vacuum tube

A travelling wave tube shows how far vacuum electronics has come.


Mention vacuum tubes and some people (those old enough and/or historically minded) might think of ENIAC, the first electronic digital computer, which made use of 19,000 vacuum tubes when it debuted in 1945. Or maybe they’d call to mind those Eisenhower-era TVs that you had to let “warm up” before the picture became clear. In other words, outdated, dinosaur technology.

But, in fact, variations of vacuum tubes are still essential to a variety of technologies, such as radars, microwaves (which at one time were referred to as “radar ranges”) and satellite communications. And if the Defense Advanced Research Projects Agency has its way, they’ll have a new use, as high-powered transmitters in the electromagnetic spectrum.

The agency is looking for new ways of producing vacuum electronic devices, or VEDs, that get around the expensive, labor-intensive process now required to produce them, according to Broad Agency Announcement soliciting ideas.

The basics of VEDs—which include the traveling wave tubes used in satellites, as well as klystrons, crossed-field amplifiers, magnetrons and gyrotrons, among other devices—date to the first half of the 20th century, although their technology has been improved significantly. With its Innovative Vacuum Electronic Science and Technology (INVEST) program, DARPA now wants to go further, looking for advanced, innovative approaches to modeling and manufacturing them.

Why? Because the electromagnetic spectrum is getting crowded and the Defense Department not only has to make more efficient use of it, but it also is increasingly concerned about operating in contested environments where adversaries could jam or otherwise interfere with signals that are essential to military operations.

VEDs that could operate in the millimeter range—high frequencies and short wavelengths—would produce a stronger signal than what’s used now, making them harder to jam, DARPA said. And it also would open up a new swath of the spectrum that isn’t currently available. The challenge is finding efficient, affordable ways to develop and produce them.

“Any time you need to operate at the outer reaches of the power-frequency parameter space, vacuum tubes are the technology of choice,” Dev Palmer, program manager for INVEST in DARPA’s Microsystems Technology Office, said in a release.  “But at the high millimeter-wave frequencies of interest to this program, the design and construction of VEDs is an intricate, labor-intensive process that requires exquisite modeling tools, exotic materials, and expensive, high-precision machining.”

DARPA is planning to award contracts for research projects looking into the aspects of developing VEDs that can operate at millimeter-wave frequencies above 75 GHz, including physics-based modeling and simulation, innovative component design, electron emission processes, and advanced manufacturing methods, including possibly 3D printing.

“As you push frequencies up, you can’t use conventional manufacturing techniques anymore,” Palmer said, because of the intricate, ultraprecise alignments required for millimeter-wave VED components. “If you could print the whole structure with a 3-D printer, so that everything was aligned right off the assembly line, it would make it much easier.”

Responses to the BAA are due by Oct. 30.

About the Author

Kevin McCaney is a former editor of Defense Systems and GCN.

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