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  • Wedgetail's Radar -- What Was Wrong and What Fixed It
    Posted by David A. Fulghum 9:01 AM on Feb 02, 2011

    Australia’s new airborne early warning and control aircraft has arrived, but it is at least four years late.

    blog post photo

    The Australian military was stunned in 2006 to discover that the Wedgetail’s large, futuristic, long-range radar still had both hardware and software problems.

    The first problem involved the “end-fire” portion of the radar that provides the fore and aft segment of its 360 degree coverage. A long, hollow chamber atop the radar had been carefully shaped to deflect a portion of the radar’s beams 90 degrees from the vertical to the horizontal, accelerate and shape those beams into waves and fire them both ahead and behind of the aircraft. The fore and aft scanning filled in the coverage between side arrays that looked left and right.

    The “top hat” chamber should have acted like a well-designed music hall to carry the music undistorted to the audience in the back rows. Because the technology was new, the original chamber fitted above the vertically-firing, transmitter modules (that created the fore and aft transmissions) was built 4-in. too short. The result was an electronic cacophony of distorted signals.

    However, the top hat with its end-fire array, positioned atop the radar’s dorsal fin, was new technology developed for the Wedgetail program. Engineers were inventing the theory to build the radar which involves over 1,000 radar signal radiators that feed the long, narrow pedestal array. The radiators assigned to fore and aft coverage point straight up from what is called the “bed of nails” [referring to the rows of hundreds of emitters on the floor of the cavity].

    The antenna modeling, which was being invented during the early stages of the program, “indicated there needed to be a 10-in. separation” between the radiating surface and the top of the radome cavity,” says Bob Hendrix, chief architect for Northrop Grumman’s ISR systems division. “This separation ultimately proved insufficient during testing, causing a partial redesign of the radome and perturbation to the program.”

    The end-fire design creates a traveling plane wave that grows in power as it moves either forward or backward along the cavity. But because the space was too narrow, the phasing of the wave did not allow it to be strengthened and shaped properly by the subsequent rows of emitters.

    “It’s like an orchestra where the conductor needs to make sure that each musician does not absorb or distort the sound from the others,” Hendrix says.

    Designers created a program to increase the outer mold line of the aircraft, but that created an aerodynamic impact which had to be defined and compensated for by a new series of wind tunnel tests that added to the delay.

    “These L-band T/R modules are very high power because they have to see hundreds of miles in all directions,” Hendrix says. “Fighters have a more limited scan [perhaps 120 degrees or less] and don’t have to look that deep. Now we have very stable hardware and software so that we can make many improvements – perhaps for a 10-year window – with software modifications. “

    A second, longer-lasting problem was refining the software for the baseline Wedgetail missions and capabilities that were constantly evolving as electronically scanned array radar technology matured.

    “Part of what took so long was wrapped up in [tweaking the software],” Hendrix says. “We had to optimize the radar and IFF [automated identification friend or foe] processing to pull tiny targets out of cluttered backgrounds. You are always challenged by the false alarm rate. You have to reduce that for the surveillance operators.

    But again, the benefits -- shrouded in classification -- may be worth the wait. They include, given enough funding for software development, capabilities such as focusing radar beams on a single point to serve as anti-missile weapons or generating data beams that can be packed with algorithms to invade enemy communications networks.

    When the available power is focused through a smaller sector of coverage, the output goes up which allows the detection of smaller objects at longer range. The new target set includes stealthy cruise missiles and aircraft now under development by Russian and Chinese industries for export. Greater computing power allows the easier identification of objects whether they are moving or not.

    Tags: ar99, Wedgetail, AESA, RAAF

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