WRIGHT-PATTERSON AFB, OH – US military researchers needed a company to develop broadband adaptive RF filters and compensators to enable the use of broadband software defined radio in congested and contested environments. They found their solution from L3Harris Technologies Inc. Communications Systems-West segment in Salt Lake City.
Officials at the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio, announced a $7.2 million contract with L3Harris on Wednesday for the Wideband Adaptive Radio Frequency Protection (WARP) project.
When exposed to interference and self-interference, these filters and compensators will sense and automatically adapt to the electromagnetic environment through the intelligent management of their adaptive hardware. The idea is to mitigate interference – especially in contested environments – selectively and protect broadband digital radios from saturation.
The Air Force Research Laboratory awarded this electronic warfare (EW) contract with L3Harris on behalf of the US Defense Advanced Research Projects Agency (DARPA) in Arlington, Virginia. Additional WARP contracts may be awarded.
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Digital receivers have historically been narrowband because they are limited by the bandwidth of the A/D converter, the researchers explain. For these narrowband systems, preplanned filtering prevents unwanted signals from reaching the A/D converter.
In the last decade, however, ADC technology has achieved more than 10 GHz of instantaneous bandwidth with 8-10 effective number of bits (ENOB).
This performance is sufficient for wideband digital receivers, but poses two challenges: wideband analog-to-digital converters typically have relatively little available input voltage variation and reduced dynamic range compared to their narrowband counterparts; and as the bandwidth increases, more signals are seen, which means larger voltage swings in the A/D converter.
The DARPA WARP program seeks to protect these wideband receivers against external and intrinsic interference by adaptively equalizing the input spectrum to stay within the dynamic range of a wideband digital receiver.
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Today, receivers are protected from external interference by static filtering, automatic gain control, or signal limiters. Still, static filtering uses only a fraction of the digital receiver’s bandwidth, giving good sensitivity but not taking advantage of the receiver’s available bandwidth. Meanwhile, automatic gain control takes advantage of the system’s bandwidth, but reduces sensitivity to small signals.
At the same time, signal limiters can cause cross-modulation distortion and can reduce overall system sensitivity. Tunable filters are sometimes a solution, but rarely can be tuned above the achievable bandwidth.
Instead, the WARP program aims to develop wideband, adaptive filters and analog signals that selectively attenuate or cancel external and intrinsic interference to protect wideband digital radios from saturation, ultimately enabling the use of software-defined radios in congested and dynamic spectral environments.
An ideal broadband receiver would adapt to EW muting or blocking to maintain dynamic range without reducing sensitivity and bandwidth. the WARP project seeks to develop adaptive filters to automatically reconfigure their frequency response to include pass/stop bands with bandwidth and center frequency tuning and to selectively attenuate large signals while passing small or desired signals.
The challenge is to do this over a wide bandwidth with low insertion loss at the receiver input. Today, most chip-scale tunable filters are limited to a tuning ratio of 2:1 or less without explicit bandwidth switching.
Instead, the WARP program seeks to demonstrate adaptive RF filtering of external interference with a 9:1 tuning ratio to provide full band coverage across 218 GHz with new filter architectures based on state-of-the-art components and packaging.
The WARP program consists of two four-year technical areas: broadband adaptive filtering; and broadband signal cancellation. For more information, contact L3Harris Communications Systems-West online at www.l3harris.com/capabilities/defenseThe Air Force Research Laboratory in www.afrl.af.milor DARPA at www.darpa.mil.
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