The RF spectrum environment is rapidly evolving. To achieve superiority in electromagnetic spectrum (EMS) operations in the modern era—including over adversaries gaining ground in the domain—requires higher-level performance and flexibility in critical elements. One area of priority: heightened multifunctionality and granular optimization in active electronically scanned arrays (AESAs).
DARPA’s work has long targeted foundational technological challenges and advances that provide U.S. forces a decisive edge. Acutely attuned EMS capabilities are crucial enablers for mission-critical situational awareness and tactical communications. Unlike limited, narrowband phased array systems, wideband AESAs employ hundreds or thousands of tiny antenna elements that can all transmit and receive signals.
To help solve multifaceted and mounting challenges, DARPA has selected the research teams for the COmpact Front-end Filters at the ElEment-level (COFFEE) program, which seeks to create a new class of integrable, high frequency filters with low loss, high-power handling and seamless uniformity. The selected teams will be led by Northrop Grumman, Raytheon, Akoustis, BAE Systems, Metamagnetics, Georgia Institute of Technology, Columbia University, Carnegie Mellon University, University of Michigan, University of Texas at Austin and University of California at Los Angeles.
An AESA’s ability to dynamically reconfigure radar beams and communicate across a range of frequencies is especially important in congested environments. This versatility remains key in military operations: resistance to signal jamming and interception while capable of mapping, navigating, sensing, tracking, visualizing and creating high-bandwidth data links for cross-domain operations. However, AESAs and broader EMS advances must evolve proactively and progressively to maintain and accelerate the U.S. technological advantage.
The COFFEE program will focus on creating an integrable filter technology to mitigate interference and maximize performance across a challenging S-Band through Ku-Band (i.e., 2 GHz to 18 GHz) frequency range. These filters must not only distill signals across the expansive frequency range, but do so while physically bound within an 18 GHz half-wavelength array pitch (i.e., 69 mm², a space smaller than a dime). This new filter technology will account for digital-at-every-element advances—impacting each of an AESA’s hundreds or thousands of tiny antenna elements—for high frequency systems facing increasingly unacceptable tradeoffs in size, weight, performance and interoperability.
“With the Defense Department-wide emphasis on electromagnetic spectrum superiority, our AESAs are tasked with a heightened demand for greater range, volume and function. These demands are magnified by trends toward wider bandwidths and digitization at the level of the individual element,” said Dr. Benjamin Griffin, the program manager leading the COFFEE program. “There is very little room to integrate conventional filter technologies, exposing each element to the full bandwidth of potential threats. Today, there is no integrable filtering technology to meet these compounding requirements.”
The primary focus area of the program will leverage emerging microelectronics materials, integration and design to build integrable filters, advancing new classes of miniaturized resonators as the building blocks. An additional, forward-looking focus area is oriented around millimeter-wave frequencies (demonstrating performance at 50 GHz), targeting fundamental limits of compact resonators beyond 18 GHz.
“DARPA has been at the forefront of creating opportunities for multifunctional AESAs, with programs such as Arrays at Commercial Timescales (ACT),” Dr. Griffin said. “COFFEE is expected to establish an integrable filter technology for Defense Department AESAs, but this work will also have implications in commercial mobile sector advances expected in the near future.”
The COFFEE program, which is expected to run for 50 months across three phases—an 18-month base Phase I and two 15-month option phases—is a part of DARPA’s Electronics Resurgence Initiative (ERI) focused on advancing the U.S. semiconductor industry. The program addresses part of ERI’s focus on revolutionizing communications for the 5G era and beyond. Research will kick off in the spring of 2022.