Phased radio frequency (RF) arrays use numerous small antennas to steer RF beams without mechanical movement. Phased array antennas are a type of antenna array that comes with the feature of electronic steering to change the direction and shape of radiated signals, without any physical movement of the antenna. The phase difference between the radiated signals from each antenna in the array is responsible for this electronic steering. The fundamental principle of the phased array antenna is the phase-dependent superposition of two or more radiated signals. When the signals are in-phase, they combine together to form a signal of additive amplitude. When the signals are counter-phase, they cancel each other.
Today’s critical DoD applications such as radar, communications and electronic warfare use antenna arrays to provide unique capabilities, such as multiple beam forming and electronic steering. Their lack of moving parts reduces maintenance requirements and their advanced electromagnetic capabilities, such as the ability to look in multiple directions at once, are extremely useful in the field. They also provide with increased range and power, agility and sensitivity, reliability and multi-function capability.
These benefits, though, come with a high price tag. Current DoD array development programs can take more than a decade and cost tens of billions of dollars. One of the main factors driving the dollar and time costs of current phased array programs is the need to start engineering from scratch, to customize the array to a specific defense application every time a new system is needed such as a radar system for a single class of warship. Because the resulting arrays are so specialized, even upgrading them is often prohibitively expensive.
The wider use of arrays has been limited by lengthy system development times and the inability to upgrade already- fielded capabilities—problems exacerbated by the fact that military electronics have evolved at a slower cadence than in the commercial sector.
The drawn-out process for designing and building custom arrays also means that actual gains in performance have slowed to the point that commercial-off-the-shelf electronics are catching up rapidly in their ability to counter phased arrays. This emerging parity threatens to diminish the technological advantage DoD has traditionally enjoyed in military electronics. A technical solution is needed to bring military array programs to more manageable cost levels and timescales.
U.S. military researchers in 2014, planned to spend more than $100 million, involve at least seven defense companies, and award at least nine separate contracts in a landmark project to speed development of electronic RF phased array antennas for communications, signals intelligence (SIGINT), radar, and electronic warfare (EW).
DARPA created Arrays at Commercial Timescales (ACT) with aim to shorten design cycles and in-field updates and push past the traditional barriers that lead to 10-year array development cycles, 20- to 30-year static life cycles and costly service-life extension programs. ACT program seeks new technologies to form a shared hardware basis for many future DoD phased array development programs. Specifically, as an alternative to large undertakings focused on traditional monolithic array systems, ACT seeks to develop a digitally-interconnected building block from which larger systems can be formed. The desired building block, composed of a common module and a reconfigurable EM interface, would be scalable and customizable for each application, without requiring a full redesign for each application space.
The ACT program has three thrusts: Digitally- interconnected common building module for insertion into a wide range of applications; Reconfigurable and tunable RF interface from S-band to X-band frequencies (and points between) and over-the-air coherent array aggregation.
One of the main challenges in realizing this vision is the implementation of a common RF front-end that can be used to down/up covert RF signals over a wide range of center frequencies and bandwidths to within the analog bandwidth of typical data converters.
Each of the two thrusts, each focused on a specific enabling technology for rapidly upgradable and widely deployable array architectures:
- A digitally-influenced common module comprising 80 to 90 percent of an array’s core functionality for insertion into a wide range of applications
- Reconfigurable and tunable RF apertures for spanning S-band to X-band frequencies (and points between) for a wide variety of characteristics
We want to give those efforts a common foundation. Success with technical areas one and two would lead to a significant reduction in program costs, namely the 30-40 percent nonrecurring engineering costs these programs average. We’ll also save time, allowing DoD to field the effective new systems and readily refresh systems already in the field. Because of the rapid evolution of electronics, cost and time translate directly to performance. So not only do we hope to make arrays significantly cheaper at a faster time scale, we believe that this will in turn allow for much greater performance.”
The third technological area of ACT aims to reduce the space requirements for defense electronics by developing distributed phased arrays that can communicate with each other to function as a single larger array. For example, there is very limited space available in the tower of an aircraft carrier, so large systems for applications like radar do not always fit. ACT could enable just a piece of a radar system to be hosted in one location, with other pieces hosted elsewhere in the carrier group, and with all the pieces communicating to act as a whole. This portion of ACT expands on the work done under DARPA’s Precision Electronic Warfare (PREW) program, applying the basic capability of time and localization transfer to next generation arrays. The time and localization work done under PREW helps precisely put energy on target from disparate origin points.
“What DARPA is looking for is essentially three tiers of technology that together form a configurable system that would serve as a starting point for any new array program,” said Bill Chappell, DARPA program manager for this effort.
If ACT is successful, the resulting technologies may save DoD billions of dollars and require years less research and development time for new systems. ACT will oversee technology research into three technical areas: 1) a common building block for RF arrays, 2) a reconfigurable electromagnetic interface (the antenna interface from the electronics to the waves in the air) and 3) over-the-air coherent array aggregation.
ACT program Awards
The list of companies involved in the DARPA ACT program are Raytheon, Northrop Grumman, Lockheed Martin, Boeing, Rockwell Collins, HRL Laboratories, and Georgia Tech Applied Research.
Raytheon Integrated Defense Systems (IDS)
Specifically, experts from Raytheon Integrated Defense Systems (IDS) in one contract will concentrate on developing a common hardware module applicable to many different array functions, as well as combining arrays on separate platforms into a larger aperture with precise timing and localization.
“Raytheon shares DARPA’s vision of a common digital beamforming architecture platform to enhance affordability and upgradability,” said Paul Ferraro, vice president of Advanced Technology Programs for Raytheon’s Integrated Defense Systems business. “The RAPID programs are the latest example of Raytheon’s collaboration with DARPA to provide affordable, rapidly available, best in class solutions that can stay ahead of evolving threats.”
Raytheon is leveraging its Rapid Array Performance Improvement and Deployment (RAPID) concepts in support of the ACT program, the firm says. RAPID aims to dramatically shorten the timescales and non-recurring cost associated with phased array development, deployment and performance upgrades. RAPID achieves this by creating a building block, composed of a digitally-influenced common module and a reconfigurable radiating antenna element, that is scalable and customizable for each application, without requiring a full redesign for each application space.
Georgia Tech researchers have proposed a reconfigurable electromagnetic interface (REI) with an integrated reconfigurable ground plane that can be optimized in-situ for frequency, bandwidth, beam pattern, steering, null placement, polarization, and input impedance.They plan to capitalize on the gain of the array to match the gain of the standard array, but with added ability to reconfigure for different missions, to train to its environment, and to require a lower feed density and lower common module density than a traditional array.
Boeing, meanwhile, has proposed a novel RF phased array antenna (PAA) composed of reconfigurable wideband elements. Boeing researchers will scale the device for configurability within the 2-to-12-GHz frequency range but this technique could be scaled to other frequency bands as well.
The reconfigurable Boeing array should be modifiable in the field to support common module changes or emergent mission requirements. Reconfigurable arrays have persistent challenges in four main technological categories: array element performance; low-loss switches; controlling switches without hurting array performance; and fabricating interconnect structures.
The DARPA ACT program also seeks to combine arrays on separate platforms into a larger aperture with precise timing and localization. The goal is to create electromagnetic interface arrays that can be fielded at a rate to match that of commercially developed electronic components.
MACOM SPAR™ Tiles was Selected by Massachusetts Institute of Technology’s Lincoln Laboratory as Testbed for the DARPA ACT Radar Development Program
MACOM’s SPAR tile technology has also been selected by MIT LL for use in a test bed for DARPA’s Arrays at Commercial Timescale (ACT) program in which the SPAR tiles will interface with commercial back-end electronics to explore the potential to achieve new capabilities in digital phased arrays for next-generation radar, electronic warfare and communications systems.
SPAR Tiles are RF assemblies containing antenna elements, GaAs and GaN semiconductors, transmit and receive modules and RF and power distribution networks. When combined with additional signal generation and receive and control electronics, the composite assembly forms the building block for the MPAR planar active electronically scanned antenna (AESA) for the radar system.
The planar tile approach is designed to leverage the economies of scale associated with commercial production based on surface mount technology that allows for the use of low cost plastic packaging for the TRM MMICs and automated assembly.MAOM’s S-band MPAR program is designed to upgrade the capabilities using AESA architectures underpinning a planar array capable of demonstrating multi-function operation using modern, dual-polarization technology. The ability to combine weather radar and aircraft tracking radar systems using a single radar is designed to translate into savings to the US taxpayer approaching $4.8 billion as it would obviate the need to operate approximately 350 aircraft tracking radar systems and 200 weather radar systems. The ultimate aim is to replace these discrete systems that are operated by multiple operators with approximately 365 multifunctional radar systems based on the MPAR program with the output networked together to allow the National Weather Service (NWS) to use the data for its weather mission requirements.
DARPA posts ACT-IV PUCK RFI
In October 2019, the Defense Advanced Research Projects Agency posted a request for information on ACT-IV PUCK Aperture. This Request for Information from the Defense Advanced Research Projects Agency’s (DARPA) Microsystems Technology Office (MTO) seeks information on phased array aperture design and fabrication methods that reduce Non-recurring Engineering (NRE) costs and enable the DoD to realize the full impact and performance of reconfigurable, programmable, and software defined functionality of hardware assets.
This RFI is seeking information about the current practices and limitations of building radio frequency (RF) personality systems that DARPA intends to use to develop a future ACT-IV PUCK Aperture Broad Agency Announcement (BAA).
To maintain technology dominance, the Department of Defense (DOD) is developing next generation systems that support reconfigurable, programmable, and software definable functionality in the electromagnetic spectrum (EMS). Such technology now drives the next generation of phased array technology, which will be built on top of highly flexible, scalable, and reconfigurable RF phased array digital backends. These digitized array modules operate over wide frequency bands and support many independent transmit and receive (i.e., Tx/Rx) channels in a low size, weight, and power (SWaP) form factor.
Such digital architectures enable a single array to perform multiple functions (e.g., RADAR, communications, signal intelligence/electronic intelligence, and electronic warfare (EW)). As such, these digital solutions should significantly reduce the NRE of fielding specific array capabilities because of the commonality within the electronics, the ease of upgradability, and transfer of software modes. In general, the future flexibility needed by the next generation arrays is pushing towards common and standardized interfaces that allow for the separation of an RF frontend and the digital backend, also known as a digital receiver/exciter (DREX).
When separating the front and backends, the DOD requires custom array apertures with specific “RF personalities” to support mission-specific requirements in terms of amplification for appropriate power, filtering for interference management, and analog subarrays when the additional element count is required. The cost and fabrication schedule of these custom apertures often counter-acts the modularity and operational relevance of deploying next generation arrays despite capable DREX backends. This effort, known as Puck, is part of DARPA’s Arrays at Commercial Timescales – Integration and Validation (ACT-IV) program.
Northrop Grumman Delivers Advanced Multifunction Sensor System to AFRL and DARPA in August 2021
Northrop Grumman Corporation has delivered the Arrays at Commercial Timescales Integration and Validation (ACT-IV) system to the Air Force Research Laboratory (AFRL) and Defense Advanced Research Projects Agency (DARPA). The system is based on an advanced digital active electronically scanned array (AESA) that completed multiple successful demonstrations and acceptance testing at Northrop Grumman test facilities.
“The development of the ACT-IV system is a breakthrough in AESA performance and marks an important milestone in the nation’s transition to digitally reprogrammable multifunction radio frequency (RF) systems,” said William Phillips, director, multifunction systems, Northrop Grumman. “The new ACT-IV capabilities have the agility to defeat complex emerging threats and will be used to enhance the next generation of integrated circuits and AESAs that are currently in our digital AESA product pipeline.”
ACT-IV is one of the first multifunction systems based on a digital AESA using the semiconductor devices developed on the DARPA Arrays at Commercial Timescales (ACT) program. By applying the flexibility of the digital AESA, the ACT-IV system can perform radar, electronic warfare and communication functions simultaneously by controlling a large number of independent digital transmit/receive channels. The agility of the digital AESA was demonstrated during multiple demonstrations at the Northrop Grumman test range and will enable future warfighters to quickly adapt to new threats, control the electromagnetic spectrum, and connect to tactical networks in support of distributed operations.
The ACT-IV system will be a foundational research asset for the Department of Defense’s multi-service research initiative for digital radars and multifunction systems. This initiative will support a community of researchers that are developing new algorithms and software to explore the possibilities of next generation digital AESAs for national security missions. The algorithms, software and capabilities developed on ACT-IV will transition into next generation multifunction RF systems to support advanced development programs throughout the Department of Defense.
“This delivery is the culmination of the close collaboration between the teams at AFRL, DARPA and Northrop Grumman,” said Dr. Bae-Ian Wu, ACT-IV project lead, Sensors Directorate, AFRL. “The ACT-IV system is being prepared for initial testing by the AFRL Sensors Directorate as part of a strategic investment to develop and test the technologies for multifunction digital phased array systems in an open-architecture environment for the larger DoD community.”