antenna for Navy
COMPUTER PROGRAM HELPS DESIGN NEW ANTENNAS FOR NAVY SHIPS
COLUMBUS, Ohio -- A computer program developed at Ohio State University has enabled the U.S. Navy to design a new system of antennas that reduces radio interference and makes its destroyers less visible to enemy radar.
The same program will also design antennas for buildings, trucks, cellular phones -- even the future International Space Station.
Ronald Marhefka, senior research scientist and adjunct professor of electrical engineering at Ohio State and his colleagues developed the program, which they call Numerical Electromagnetics Code - Basic Scattering Code (NEC-BSC). The NEC-BSC program traces the path of electromagnetic waves such as radio signals as they stream outward from antennas.
For example, said Marhefka, if someone inside a room tries to use a cellular phone, some of the electromagnetic waves from the phones antenna will bounce off the wall, and scatter in all directions. Others will pass through. Where the waves cross, they clash with each other, and the person using the phone will hear interference. We wanted to develop a program that people could use to visualize the flow of energy from antennas and design the structures around them to eliminate interference.
Marhefka used the program to draw up plans for the Navys new antenna structure, the Advanced Enclosed Mast/Sensor (AEM/S) System. The Navy debuted the AEM/S system on one of its destroyers, the USS Arthur W. Radford, in September 1997.
Like all destroyers in the modern Navy, the Radford sported a main mast, a reminder of the days of wind-powered sea travel. These days, masts carry radar and communications antennas instead of sails.
The signals from ships antennas sometimes interfere with each other. And, because the antennas must operate outside in harsh weather, the Navy constructs them of durable -- and heavy -- materials that weigh ships down.
For these reasons, the Navy decided to replace the main mast on the Radford with an experimental radome, an 87-foot high, 35-foot wide plastic and fiberglass hexagonal shelter that encloses its antennas and deflects radar.
A radome is an enclosure that allows an antenna to operate as if it were out in the open. It acts like a window; it protects the antenna inside, but allows the radio waves to go through, said Marhefka.
Because the radome blocks out the harsh weather, the Navy will be able to construct its antennas of lighter materials. The angles on the radome also deflect incoming radar signals, so the ship will be less visible to the enemy.
The Navy gave Marhefka its plans for the shape of the radome, and the computer program calculated the best placement of antennas within the structure to minimize interference.
Along with another program developed at Ohio State, NEC-BSC enabled Marhefka, his colleagues, and the Navy to design a frequency-selective surface (FSS), an adjustable plastic screen for the radome that transmits certain signals while blocking others.
The FSS is like a spaghetti strainer, where the water goes through the holes but the spaghetti stays put. We designed the holes in the FSS so that some frequencies of energy will pass through and others wont, Marhefka explained.
While the Navy unveiled the AEM/S system on the Radford in September, the ship wont return to normal fleet service until later in 1998, after it receives scheduled maintenance. The Navy plans to test the AEM/S system at sea for at least a year, and then Marhefka and his colleagues will use the NEC-BSC program to further improve the system.
For this first trial run, the Navy used the same standard antennas as always, so theyre still heavy, said Marhefka. Were going to help them design lighter antennas that are also multifunctional.
Currently Marhefka is adapting the AEM/S system technology to fit the LPD 17, the Navys next generation of amphibious transport dock ships.
While this work was funded by the Navy, the technology also holds non-military applications; Marhefka said the program helps design antennas for buildings, trucks, and cellular phones.
For example, he and his colleagues have worked with a trucking company to install antennas behind the domes on top of tractor-trailer cabs, so that the company may track its drivers on the road.
NASA is using Marhefkas code to plan the position of antennas on the future International Space Station.#
Contact: Ronald Marhefka, (614) 292-5752; Rjm@ESL.eng.ohio-state.edu
Written by Pam Frost, (614) 292-9475; Frost.email@example.com
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