Normal radios operate in kilohertz (kHz) and megahertz (MHz) frequencies, bandwidths corresponding to electromagnetic oscillations in the thousands and millions of cycles per second ranges, respectively. Upping the ante, cell phones and radar systems operate in the billions of cycles per second range—that is, gigahertz (GHz) frequencies. But no one has managed to push radiofrequency technology into the trillions of cycles per second, or Terahertz (THz), range. With the Terahertz (THz) Electronics Program, however, DARPA has begun to make it possible. And as graphically depicted in the attached DARPA “fight” poster—fashioned after a promotion for the legendary bout in 1975 between Muhammed Ali and Joe Frazier in Manila, the Philippines—two promising and powerful approaches are dueling it out for possible dominance in this high-frequency electromagnetic frontier.
In one corner is the Solid State Power Amplifier (SSPA), which in 2014 was certified by Guinness World Records as the world’s fastest solid state chip, able to operate at THz speeds. This device, made of the semiconductor indium phosphide (InP), also can boost the power of a wide swath of incoming signals some thirtyfold (that’s what the “15 dB GAIN” spec in the poster indicates). In the other corner is a micromachined Traveling Wave Tube Amplifier (TWTA), a miniaturized device that relies on a tiny vacuum chamber in which electrons and radio signals interact. This wee bruiser can boost the power of a narrower range of THz frequencies by a factor of about 200 and was a celebrated darling of the 2016 IEEE International Vacuum Electronics Conference.
Of course, in reality this need not be a fight. “Really, the two contenders, both of them made by Northrop Grumman, are working as a tag team to collectively smack down the technical barriers that until now have made many THz applications impossible to realize,” said Dev Palmer, the DARPA program manager who has overseen the two-pronged research effort. “Together, the world-record SSPA and highly-acclaimed TWTA open the way to a THz future featuring devices that can generate, detect, process, and radiate extremely high-frequency signals, and push what is possible in areas ranging from high-resolution security imaging, collision-avoidance radar, high data rate communications, and remote detection systems for dangerous chemicals and explosives.”