DARPA Developing New Filtering Technology for Wideband Arrays Operating in Congested RF Environments

To address the challenges hampering the use of next-generation wideband arrays in congested wireless environments, DARPA has developed the COmpact Front-end Filters at the ElEment-level (COFFEE) program. COFFEE aims to develop a new class of integrable, high-frequency RF filters for wideband Active Electronically Scanned Arrays (AESAs) that are compact, high performing, and enable protection at every element of the array.

COFFEE is a part of DARPA’s Electronics Resurgence Initiative (ERI) – a five-year, upwards of $1.5 billion investment in the advancement of the U.S. semiconductor industry. The program addresses part of ERI’s focus on revolutionizing communications for the 5G era and beyond.

DARPA has spent decades advancing technologies that provide enhanced situational awareness, perhaps most notably phased arrays. Having the ability to detect and monitor adversarial movement or communications provides a significant advantage to U.S. military operations. For pilots in air-to-air combat, for example, advanced radar capabilities arguably give a more decisive edge than a higher maximum speed.

The current leading edge of phased arrays is the Active Electronically Scanned Array (AESA). Unlike their passive counterparts, where all the antenna elements are connected to a single transmitter and/or receiver, AESAs employ a matrix of hundreds or thousands of tiny antenna elements, each with its transmitter and receiver. This allows you to electronically steer a beam of radio waves in different directions, instead of physically moving the antenna to point at a target.

Over the past decade, there has been increased interest in wideband AESAs with digital-at-every-element architectures. Wideband AESAs are more versatile and robust because they allow for operation at different frequencies, as opposed to narrowband arrays that are tuned for a specific use and frequency. Digital-at-every-element architectures allow AESAs to perform beamforming in the digital domain, enabling the collection of many beams simultaneously. However, the implementation of wideband, digital-at-every-element receivers in AESAs currently comes with significant trade-offs.

“Wideband, digital-at-every-element AESAs are particularly compelling for applications like advanced radar, electronic warfare (EW), and communications,” said Dr. Benjamin Griffin, a program manager in the Microsystems Technology Office (MTO). “However, high bandwidth receivers often have a limited dynamic range, leaving them vulnerable to electronic jamming. Further, digital-at-every-element exposes each element to interferers and requires filtering at the element level, leaving very little room to integrate conventional filter technologies.”

“Essentially, we want to build integrable filters that operate over a wide range of frequencies that are also small enough to fit behind each element of the phased array,” said Griffin. “COFFEE aims to develop filters that are on the analog front-end, making the array more robust and resistant to interference before digital processing on the back-end.”

The key to this research will be the development of filter technology that can address all microwave frequencies of a wideband AESA’s bandwidth without sacrificing performance. Further, the target filters must be physically small compared to the element area as the available space for element-level integration decreases significantly as AESA bandwidth increases. Finally, to ensure uniformity the COFFEE filters should be manufacturable with a reproducible performance at each of the array elements.

The main focus of the research will be on developing a new class of resonators and integrable microwave filters that address COFFEE’s technical objectives. In addition, research studies into compact mm-wave resonators will be conducted to inform new technical approaches for potential future efforts for integrable mm-wave filters.

Interested proposers will have an opportunity to learn more about the COmpact Front-end Filters at the ElEment-level (COFFEE) program during Proposers Day, which will be held on June 17, 2021, from 1:00 p.m. to 5:00 p.m. (EDT) via Zoom.

Click here to learn more about COFFEE.

Click here to learn more about AESA.