Wireless transmitters that operate at very or ultra low frequencies (0.3‐30 kHz) typically require some big antenna complexes to handle their communications.

Scientists at the Defense Advanced Research Projects Agency (DARPA) said they are interested looking to eliminate that issue and develop smaller physical structures that could handle new long-distance communication applications.

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In a Request for Information, DARPA wrote: “At these frequencies, free‐space electromagnetic (EM) field wavelengths are measured in tens of kilometers, resulting in very large transmitter structures when employing conventional antenna approaches. Electrically‐small antennas are defined as having dimensions much smaller than the EM wavelength, with examples in the literature of antenna‐sizes as small as 1/10th of the EM wavelength. DARPA is seeking innovation to bring that size below 1/10,000 of the EM wavelength or by at least a factor of 103 smaller than the current state of the art (SOA).“

Such a tremendous reduction in size is impossible to achieve through traditional antenna design so DARPA said it is looking to gather information “in the areas of materials, mechanical actuation, and overall transmitter architectures to address impedance matching, power handling, signal modulation, scalability, and other system level considerations. “

DARPA has been busy on the wireless front this year. In April a DARPA-funded research team said it had developed a tiny component for silicon-based circuitry that could double the radio-frequency (RF) capacity for wireless communications—offering faster web-searching as well as the development of smaller, less expensive and more readily upgraded antenna arrays for radar, signals intelligence, and other applications.

The work was led by Columbia University electrical engineers Harish Krishnaswamy and Negar Reiskarimian and funded under DARPA’s Arrays at Commercial Timescales (ACT) program, which is looking to develop wireless electronic components that can be integrated into larger, more advanced systems quickly. DARPA said ACT products aim to “shorten design cycles and in-field updates and push past the traditional barriers that lead to 10-year array development cycles, 20- to 30-year static life cycles and costly service-life extension programs.” In this case the creation focuses on an electrical component known as a “circulator” typically used to control the direction of signal flow in a circuit.

In March the defense research agency announced a $2 million Grand Challenge called the Spectrum Collaboration Challenge (SC2) whose primary goal is to infuse radios with “advanced machine-learning capabilities so they can collectively develop strategies that optimize use of the wireless spectrum in ways not possible with today’s intrinsically inefficient approach of pre-allocating exclusive access to designated frequencies.”

DARPA said the current practice of assigning fixed frequencies for various uses irrespective of actual, moment-to-moment demand is simply too inefficient to keep up with actual demand and threatens to undermine wireless reliability in the military as well as civilian applications, DARPA stated.

The challenge is expected to take advantage of recent significant progress in the fields of artificial intelligence and machine learning and also spur new developments in those research domains, with potential applications in other fields where collaborative decision-making is critical,” DARPA stated.

“DARPA Challenges have traditionally rewarded teams that dominate their competitors, but when it comes to making the most of the electromagnetic spectrum, the team that shares most intelligently is going to win,” said SC2 program manager Paul Tilghman of DARPA’s Microsystems Technology Office in a statement. “We want to radically accelerate the development of machine-learning technologies and strategies that will allow on-the-fly sharing of spectrum at machine timescales.”

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DARPA said it will build what it called the largest-of-its-kind wireless test bed – “the Colosseum” -- which will serve during and after the SC2 as a national asset for evaluating spectrum-sharing strategies, tactics, and algorithms for next-generation radio systems. The “Colosseum” will let researchers remotely conduct large-scale experiments with intelligent radio systems in realistic, user-defined RF environments, such as the wireless conditions of a busy city neighborhood or battle setting.

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