The defense spectrum is undergoing a quiet revolution. For decades, the upper reaches of the radio frequency domain, the millimeter-wave (mmWave) band between 30 and 300 gigahertz, have been recognized for their tantalizing potential: enormous bandwidth, pinpoint spatial precision, and directional control that promise unprecedented radar resolution and data capacity. Yet the same physics that make these frequencies appealing have also limited their use. High atmospheric attenuation, short propagation distances, and fragile power performance in electronic devices kept mmWave confined to labs, short-range links, and experimental 5G trials. That ceiling is now breaking.

The convergence of advanced solid-state amplifiers, phased-array antenna engineering, and digital beamforming algorithms is transforming millimeter-wave technology from a scientific curiosity into a cornerstone of next-generation defense systems. Ongoing work at the Defense Advanced Research Projects Agency (DARPA), MIT Lincoln Laboratory, and global partners such as NEC and NTT suggests that the era of mmWave dominance has quietly begun. It is emerging not as a single breakthrough, but as a layered evolution of physics, computation, and mission requirements.

At DARPA, Dr. Dev Palmer, program manager in the Microsystems Technology Office, has spent the last decade orchestrating research that bridges the gap between semiconductor physics and operational capability. As he explained at EMC Live 2025, DARPA’s mission has been to push the practical limits of the electromagnetic spectrum into higher frequencies, where bandwidth expands but device efficiency collapses. Historically, the power available from electronic devices decayed sharply with frequency, creating a fundamental bottleneck in designing radars or communication systems operating above 30 GHz. Amplifier efficiency, thermal management, and device noise all worsened as transistors and vacuum-electronic sources were pushed into regimes they were never designed to handle. Through coordinated programs in wideband solid-state and vacuum-electronic amplifiers, DARPA and its partners have developed hybrid architectures that combine the scalability of semiconductor manufacturing with the power-handling strength of legacy vacuum devices. The result is compact, high-efficiency transmitters capable of generating clean, high-power mmWave signals across unprecedented bandwidths.

In radar, that bandwidth translates directly into range resolution, the ability to distinguish two objects separated by mere centimeters. In communications, it yields multi-gigabit throughput and adaptive beam steering, enabling directional links that are both secure and resistant to interference. The physics are uncompromising, but the engineering has caught up.

At MIT Lincoln Laboratory, those theoretical gains have become operational reality. The Wideband Selective Propagation Radar, or WiSPR, represents one of the most ambitious integrations of radar and communication functions in a single mmWave platform. Developed for the US military, WiSPR operates in the same high-frequency range that commercial 5G networks are beginning to explore, but its ambitions are far greater: to simultaneously sense, transmit, and adapt in real time. The system uses electronically scanned phased arrays composed of hundreds of antenna elements whose individual phases are digitally synchronized. By adjusting phase relationships, the system can shape its energy into ultra-narrow pencil beams or broaden them for communication bursts.

Traditional radars rely on mechanical scanning or limited electronic steering. WiSPR’s design removes all moving parts, relying instead on the precise timing and phase control of custom radio-frequency integrated circuits (RFICs). Each RFIC is a miniature, software-governed transceiver capable of both transmitting and receiving at mmWave frequencies. Thousands of these chips operate in unison, their electromagnetic fields summing coherently in a chosen direction. The result is an agile system capable of instantaneously scanning an area, detecting a target, tracking it, and maintaining a data link, all without physically moving the hardware.

Operating at such frequencies poses serious thermal and signal integrity challenges. Even millimeter-scale power amplifiers dissipate significant heat. Lincoln Laboratory’s engineers addressed this by developing a micro-channel cooling system that removes thermal energy directly behind each transmit module, ensuring coherence across the array. Signal phase must also remain stable to within fractions of a degree to maintain constructive interference at the desired angle. The team solved this by embedding digital correction and calibration algorithms directly into the firmware, allowing real-time compensation for phase drift and temperature variation.

The implications extend well beyond radar. Because WiSPR can dynamically trade beamwidth for range, the same array can act as a high-speed directional communications link once a target or ally is detected. This multifunctional capability is central to the emerging concept of spectrum convergence, the merging of sensing, communications, and electronic warfare (EW) functions into shared hardware and shared frequency space. Tested at the military’s Aberdeen Proving Ground, WiSPR demonstrated stable performance at distances once considered beyond the mmWave’s practical range. Its long-range sensitivity challenged conventional models of attenuation, opening new possibilities for high-frequency situational awareness in contested environments.

While the United States focuses on military applications, Japanese industry is proving how the same frequency physics can revolutionize mobility infrastructure. NEC, working with NTT and NTT DOCOMO, has demonstrated mmWave communications for high-speed vehicles, a civilian parallel that underscores the universality of the technology. Using 40 GHz-band transmitters along a 150-meter-spaced test track, researchers achieved stable connectivity for a vehicle moving at 100 kilometers per hour.

The challenge, as NEC engineers explained, was managing Doppler shift, the frequency change caused by motion between transmitter and receiver, and maintaining synchronization during antenna handovers. Traditional communication systems often lose throughput during these transitions because the carrier frequency and timing fall out of alignment. The new NEC-NTT approach pre-compensates both frequency and timing at the base station before transmission. By using analog radio-over-fiber backhaul, the three base stations remained phase-coherent, effectively operating as a distributed array. The vehicle’s terminal antenna thus received a continuous, synchronized signal even while switching nodes, with minimal loss in throughput.

This technique mirrors the coherence management strategies used in military arrays like WiSPR, highlighting the deep physical continuity between next-generation civilian and defense systems. The ability to maintain phase alignment across distributed transmitters, whether fixed or mobile, defines the emerging architecture of Beyond-5G and defense communications alike.

DARPA’s amplifier work, MIT’s multifunctional radar, and NEC’s high-speed vehicular network together reveal the ecosystem forming around mmWave frequencies: high bandwidth for data, high directivity for security, and high adaptability for mobility. The technological hurdles—device efficiency, atmospheric loss, and phase coherence—are being systematically overcome through advances in materials science, semiconductor integration, and digital signal processing.

For defense planners, the implications are profound. The same physical spectrum that lets a car stream gigabits of sensor data while traveling at highway speeds can allow a drone swarm to maintain encrypted, low-probability-of-intercept communications while mapping terrain with radar precision. Millimeter-wave systems are naturally resistant to wideband jamming due to their narrow beamwidth and high carrier frequency. They support rapid frequency hopping and beam reallocation, creating resilient mesh networks that blur the traditional lines between radar, communications, and EW.

This is why military research institutions now describe mmWave as a strategic enabler rather than a specialty. The military’s adoption of WiSPR is only the beginning. As DARPA and its industry partners scale their new amplifier architectures into deployable modules, the Department of Defense is poised to build networked sensing and communication architectures that occupy the top end of the spectrum, where data is abundant, interference is minimal, and beams are too narrow to intercept.

From a physics perspective, millimeter waves are challenging; from an engineering perspective, they are transformative. The atmospheric attenuation that once limited range now provides natural isolation, reducing interference and enhancing spectral reuse. Tight directional control makes mmWave ideal for stealthy links and precision imaging. And as the underlying hardware moves from bulky waveguides to monolithic integrated circuits, scalability is becoming feasible.

The defense industry stands at the threshold of a new electromagnetic era. The radar that sees through fog at Cape Cod, the amplifier that compresses gigahertz of bandwidth into a single pulse, and the train that maintains its data link at 100 km/h all operate on the same physical principles, and all point to the same conclusion. The future of defense communications will not be won by occupying more of the spectrum but by mastering the physics of its highest frequencies.

In the electromagnetic battlespace of the 2030s, power and bandwidth will converge in millimeter waves, where science, silicon, and strategy finally align.