Rockwell Collins may be within 10 years of building radios composed almost entirely of software, thanks to progress being made through a Defence Advanced Research Projects Agency (DARPA) project. The advance will largely come from the development of a new analogue-to-digital (A/D) converter, that eliminates the need for much of the hardware inside a traditional radio.

But the benefits being pursued by Collins for DARPA's RADER (remote analogue to digital converter with deserialisation and reconstruction) programme go far beyond simplification. With a novel A/D converter that acts as a performance multiplier for conventional converters, DARPA hopes to improve military communications in dense signal environments - such as on board an aircraft carrier - where it is necessary to simultaneously perform friendly communications and detect low-power adversarial transmissions.

Achieving this requires A/D converters with unparalleled resolution and wide instantaneous bandwidth. However, according to DARPA commercial systems available today are capable of achieving high resolution or wide bandwidth - but not both at the same time.

DARPA's requirement is for an A/D converter capable of operating over a 10 GHz bandwidth range, with a dramatic improvement in signal-to-noise resolution over existing commercial off-the-shelf converters. DARPA envisions achieving this performance with a system architecture that keeps most of the A/D converter's bulk and power requirement remote from the dense signal environment - below deck, for example - where it would neither alter the ship's centre of gravity or disturb other electronic systems by adding noise to the environment.

Collins' Photonics Technology Group in Columbia, Maryland is developing a specialised, compact A/D converter that will be contained in a single silicon device. This converter will sample the electromagnetic input from an antenna at speeds up to 20GHz, capturing input signals in the 0.1-10 GHz range.

According to Ray Zanoni, principal engineering manager at Rockwell Collins' advanced technology centre, this A/D converter combines photonics - using light for amplification and signal processing - and electronics "in a very special way [that] gives us performance superior" to what photonics or electronics can do individually.

By bringing the two technologies together, Zanoni said a device can operate fast enough so that the input signals do not have to be downshifted to the intermediate frequencies that suit today's electronics-based A/Ds.

"Now the A/D is in the intermediate frequency stage," he said. "The Holy Grail is to move the A/D as close to the antenna as possible, thereby simplifying the radio."

Zanoni said the $5.3 million second phase of the programme - Collins is the only participant at this stage - will finish by the end of the year, after which the technology could be at a readiness level to develop into a radio in 5-10 years.

Of the first phase, which ended last year, Zanoni said it "retired one of the biggest risks" in the programme - whether the idea would work or not. "It does," he said.

Source: Flight International