A makeover for top-heavy Navy ships?

* If one looks at photos of modern day warships and compares them to conceptual drawings of future Navy vessels, the most striking difference is the lack of antennas on the advanced gray hulls.

It's not that future ships won't need communications, radars and electronic warfare systems. But there will be fewer masts and, as a result, noticeably less antennas and arrays poking out the tops of the deckhouses. And if the work of Office of Naval Research scientists comes to fruition, those "forests" of antennas might one day disappear altogether as radio frequency apertures are integrated into the hulls and superstructures of the ships themselves.

"We're really trying to bring about a new way of designing Navy topsides," says Betsy DeLong, deputy for transition and innovative naval prototypes in the office's command and control technologies department.

As the demand for electronic technologies aboard combat vessels grows, the sheer number of antennas that have popped up on warships has doubled in the last decade. Surface combatants that once carried only 40 to 75 antennas are now sailing with as many as 150.

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That's generating a slew of problems for sailors. Ships have limited real estate available for antennas, especially at their pinnacles. Increasing numbers of antennas mean engineers have to squeeze them in at closer proximity to other arrays.

"When you have lots of different apertures all around your topsides, you have issues of blockage, and you have issues of these antennas interfering with each other," says DeLong. Such electromagnetic interference can have detrimental effects on the functionality of combat systems below decks, particularly when multiple networks are in use. Optimizing those technologies in the saturated airwaves environment also is a challenge for engineers.

Moreover, the antennas tack on weight and throw off the ships' center of gravity. "Whatever weight you add to the mast, you have to add to the keel for stability," says Steven Russell of ONR's ships and engineering systems division.

Such increases could translate into expanding the size of hulls, which raises costs tremendously at a time when shipbuilding budgets are being squeezed.

Scientists believe that they can help reduce those costs by miniaturizing many of the antennas' electronic components--the phase shifters, the high-powered or low-noise amplifiers and others--and by integrating them into more efficient, wideband arrays that will allow the various combats systems to share frequencies.

The goal is to reduce the costs of the electronic components by as much as 60 percent.

Russell, a mechanical engineer, runs a program called aperstructures that seeks to eliminate antenna apertures on stick masts by incorporating the systems onto the sides of ships' deckhouses. By doing so, the superstructure itself becomes the aperture. Its larger size gives the antenna inherent power so that it doesn't have to rely as much on the ship's electricity to send and receive signals. Less energy consumption means the Navy might see significant cost savings there as well, he says.

ONR in the 1990s initiated the advanced multifunction radio frequency program to demonstrate the ability of a single aperture to perform multiple functions--electronic warfare, communications and radar--simultaneously. Though the aperture proved the concept would work, the arrays were not cost effective, says DeLong.

Since that demonstration, researchers have produced cost-effective multifunction narrowband apertures, and DeLong says one of the goals in the follow-on integrated topsides program is to develop affordable wideband arrays that will cover a range of frequencies from 30 megahertz to 50 gigahertz.

Because a single aperture cannot yet cover such a large swath of spectrum, the researchers also intend to investigate better ways to "architect" those apertures. They will determine which systems pair together well and the optimum amount of frequency suitable for each array.

In the future, sailors will be able to tap radio frequency resources automatically to meet their highest priority needs at any given time, says DeLong.

For example, if a ship is performing a communications function and receives warning of an incoming missile attack, it can then use the entire array for electronic attack without compromising other operations.

If the scientists are successful, their work will have a beneficial impact on other aspects of shipboard operations. Reducing the size, weight and number of antennas not only will allow ship designers to place the apertures in more optimal places, but also will reduce the radar cross section of the topside and improve the vessel's survivability, says Russell.

Funding for the integrated topsides innovative naval prototype work commences next year.

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