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The Defense Advanced Research Projects Agency (DARPA) is renowned for its forward-thinking initiatives that drive technological innovation. One such initiative, the COmpact Front-end Filters at the ElEment-level (COFFEE) program, is a testament to DARPA’s commitment to advancing science and technology. This program seeks to revolutionize radio frequency (RF) filter technology, enhancing the capabilities of active electronically scanned arrays (AESAs) and mitigating the challenges posed by signal interference.
Active Electronically Scanned Array (AESA) radar is a pivotal technology in modern military applications, offering superior performance and versatility compared to traditional radar systems. Unlike mechanical radar, which relies on physically rotating antennas, AESA radar uses an array of small, solid-state transmit/receive modules to steer beams electronically, allowing for rapid and precise targeting, tracking, and surveillance. This architecture provides several advantages, including faster target acquisition, enhanced resistance to jamming, and the ability to simultaneously track multiple targets and perform various tasks. The importance of RF filters in AESA systems cannot be overstated; these filters are crucial for mitigating interference and ensuring clear, reliable signal reception and transmission across a wide frequency range. By filtering out unwanted signals and noise, RF filters enhance the radar’s sensitivity and accuracy, making AESA radar an indispensable tool in defense for applications such as missile guidance, air and missile defense, and battlefield surveillance.
The Need for COFFEE
As the demand for wideband, digital-at-every-element AESAs grows, so does the vulnerability of these systems to signal interference. Interference is particularly problematic given the recent spectrum allocations for FutureG and satellite communications (SATCOM), which create new commercial opportunities but also risk interfering with existing Department of Defense (DoD) systems. This scenario underscores the need for innovative RF filter solutions that can effectively suppress unwanted signals while maintaining high performance.
Traditional AESAs, while powerful, are vulnerable to signal interference. The COFFEE program addressed this challenge by developing compact, high-performance radio frequency (RF) filters. TA2 takes these advancements a step further by integrating them into real-world systems.
Breakthroughs in COFFEE
The original COFFEE program, encapsulated in Broad Agency Announcement (BAA) HR001121S0031, aimed to develop compact, high-performance RF filters. These filters were designed to operate across a wide frequency range (2 to 18 GHz), offering significant size and performance improvements. The latest phase of this initiative, COFFEE Technical Area 2 (TA2), builds on these breakthroughs by integrating COFFEE filters into practical systems that demonstrate their interference suppression capabilities.
TA2: A Call for Disruptive Innovation
TA2 seeks proposals that showcase the disruptive potential of COFFEE filters. This means going beyond incremental improvements and exploring groundbreaking applications.
The primary goal of COFFEE TA2 is to validate the advancements made in RF filter technology by creating exemplars that showcase interference suppression. These exemplars must integrate COFFEE filters with external components such as switches, controls, interconnects, and tuning elements, ensuring that the filters meet performance metrics even after integration. The filters are expected to cover all or parts of the 2 to 18 GHz frequency range, with a particular emphasis on frequencies above 8 GHz. Additionally, proposals incorporating frequencies above 18 GHz will be considered if they demonstrate significant technical evidence and application impact.
Some key areas of interest include:
- Frequency Range: Proposals are encouraged to explore frequencies above 8 GHz, pushing the boundaries of TA1.
- Manufacturability: Solutions that leverage domestic manufacturing capabilities are preferred.
- Disruptive Potential: Proposals should demonstrate how the technology can radically transform existing practices.
Key Features and Metrics
TA2 is a single-phase, 18-month program focusing on integrating COFFEE filters with external components like switches and controls. The goal is to deliver filter tiles that meet specific performance metrics and size constraints. Here’s a breakdown of the key aspects:
Metrics: Proposals will be evaluated based on factors like insertion loss, bandwidth, and power handling, as defined in the official BAA. To achieve its objectives, COFFEE TA2 focuses on several critical performance metrics:
- Filter Center Frequencies: 2–18 GHz
- Maximum Filter Insertion Loss: < 2 dB
- Maximum Filter Architecture Insertion Loss: < 3 dB
- Instantaneous Bandwidth: > 5% of the center frequency
- Out-of-Band Rejection: > 30 dBc
- Selectivity: > 20 dBc
- In-Band Power Handling: > 30 dBm
- In-Band/Out-of-Band Input Third-Order Intercept Point (IIP3): > 10 dBm / 40 dBm
- Maximum Frequency Variability: 0.5% of the nominal frequency
- Maximum Filter Area: < 69 mm² divided by the number of filters required to cover the frequency range
- Constraints: Filter size, power consumption, and temperature stability are crucial considerations.
- Deliverables: The program requires a final report detailing the demonstration, simulations, transition strategy, construction methods, and test results.
These metrics are designed to ensure that COFFEE filters can handle high power, maintain low insertion loss, and offer broad bandwidth and selectivity, all within a compact footprint.
Addressing Technical Challenges
Integrating COFFEE filters into functional systems presents several challenges. For instance, the addition of external components can degrade performance and increase the overall size of the filter component. COFFEE TA2 seeks innovative architectural solutions to overcome these challenges, ensuring that the integrated filters maintain their high performance and compact size. Proposers are encouraged to highlight the technical risks associated with their approaches and outline mitigation strategies.
Program Structure and Deliverables
COFFEE TA2 is structured as an 18-month, single-phase effort, with a focus on rapid development and demonstration. Key milestones include:
- A program kickoff meeting at the start
- A preliminary design review within three months of kickoff
- A demonstration of all technical metrics approximately one month before the end of the period of performance
- Delivery of exemplar for independent verification and validation
The final deliverable is a comprehensive report detailing the demonstration, simulations, transition strategy, construction method, and test results, providing a clear picture of how the integrated filter meets or exceeds the specified metrics.
Conclusion
DARPA’s COFFEE program exemplifies the agency’s dedication to pushing the boundaries of technological innovation. By developing and integrating compact, high-performance RF filters, COFFEE TA2 aims to provide revolutionary solutions to the challenges of signal interference in modern and future communication systems. This initiative not only promises significant advancements for the DoD but also holds the potential to impact commercial applications, driving forward the capabilities of wideband, digital-at-every-element AESAs.
