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DARPA serves up COFFEE to develop filters for new wideband arrays

Coffee experts know that choosing the right filter can be key to brewing the perfect cup of joe. So it's fitting that the Defense Advanced Research Projects Agency's (DARPA's) new program to develop filters for wideband active electronically scanned arrays is known as COFFEE (COmpact Front-end Filters at the ElEment-level).

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 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 own transmitter and receiver. This allows one 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 DARPA's 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.”

To address the challenges hampering the use of wideband AESAs in congested RF environments, DARPA developed the COFFEE program. COFFEE aims to develop a new class of integrable, high-frequency RF filters for next-generation wideband arrays. The COFFEE filter technology will address the combination of size, performance, and reproducibility to enable protection at every element of a wideband AESA.

“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,” Griffin said. “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.”

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 reproducible performance at each of the array elements.

A 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.

COFFEE is a part of DARPA’s Electronics Resurgence Initiative (ERI) – a five-year, more than $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.

Read more: https://www.darpa.mil/news-events/2021-06-10

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