WRIGHT-PATTERSON AFB, Ohio – U.S. military researchers needed a company to develop wideband adaptive RF filters and cancellers to enable use of wideband software-defined radio in congested and contested environments. They found their solution from the L3Harris Technologies Inc. Communications Systems-West segment in Salt Lake City.
Officials of the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio., announced a $7.2 million contract to L3Harris on Wednesday for the Wideband Adaptive RF Protection (WARP) project.
When exposed to interference and self-interference, these filters and cancellers will sense and adapt automatically to the electromagnetic environment through the intelligent control of their adaptive hardware. The idea is to attenuate interference -- particularly in contested environments -- selectively and protect wideband digital radios from saturation.
The Air Force Research Lab awarded this electronic warfare (EW) contract to L3Harris on behalf of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va. Additional WARP contracts may be awarded.
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Digital receivers historically have been narrowband because they are limited by A/D converter bandwidth, researchers explain. For these narrowband systems, pre-planned filtering prevents unwanted signals from reaching the A/D converter.
In the last decade, however, A/D converter technology has achieved greater 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 A/D converters typically have a relatively small available input voltage swing and reduced dynamic range when compared to their narrowband counterparts; and as the bandwidth increases, more signals come into view, which mean larger voltage swings into the A/D converter.
The DARPA WARP program seeks to protect these wideband receivers against external and self-interference through adaptive equalization of 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 through static filtering, automatic gain control, or signal limiters. Yet static filtering only uses a fraction of the digital receiver bandwidth, which gives good sensitivity but does not take advantage of available receiver bandwidth. Automatic gain control, meanwhile, capitalizes on system bandwidth, but decreases sensitivity to small signals.
At the same time, signal limiters can cause cross-modulation distortion and may decrease the overall sensitivity of the system. Tunable filters sometimes are a solution, but rarely can tune over achievable bandwidth.
Instead, the WARP program seeks is to develop wideband, adaptive filters and analog signal cancellers that selectively attenuate or cancel external and self-interference to protect wideband digital radios from saturation, ultimately enabling the use of software-defined radios in congested and dynamic spectral environments.
The ideal wideband receiver would adapt to EW jamming or blocking to maintain dynamic range without decreasing sensitivity and bandwidth. the WARP project seeks to develop adaptive filters to reconfigure their frequency response automatically to include pass/stop bands with bandwidth and center frequency tuning and attenuate large signals selectively while passing small or desired signals.
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The challenge is to do this over a wide bandwidth with low-insertion loss at the input of a receiver. Today, most chip-scale tunable filters are limited to a 2:1 tuning ratio or less without explicit band switching.
The WARP program, instead, seeks 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: wideband adaptive filtering; and wideband signal cancellation. For more information contact L3Harris Communications Systems-West online at www.l3harris.com/capabilities/defense, the Air Force Research Laboratory at www.afrl.af.mil, or DARPA at www.darpa.mil.
