Self-Adjusting Satellite Antennas

USA Today (Society for the Advancement of Education), June, 1999

Researchers at Ohio State University, Columbus, have taken a big step toward developing adjustable antennas for satellite communications. Such an antenna could change the shape of its reflector while in orbit to improve signal quality. It also could replace several traditional antennas by delivering a variety of signals for cellular phones, pagers, and global positioning systems.

Scientists previously had found that adjustable reflectors made of plastic were light enough for use in space, but too flexible to afford good shape control. Gregory Washington, assistant professor of mechanical engineering, and Hwan-Sik Yoon, a graduate student, have proven through computer simulations that thin piezoceramic patches spaced around the back of a reflector will reinforce the plastic while controlling its shape.

A piezoceramic material is a ceramic that changes shape when a voltage is applied to it, or releases a voltage when its shape is changed manually. Researchers sometimes call these "smart" materials. "When we attach this piezoceramic material to another surface and it expands, the surface bends. When it contracts, the surface bends the other way. With that movement, we're able to change the overall shape of a structure. In this case, the shape change alters the properties of the reflector or antenna itself," Washington explains.

Satellites normally must move the entire mechanism beneath an antenna to change its direction. "It's as if our eyes could only stare straight forward--to see other directions, we'd have to turn our whole head. But an adjustable antenna can make fine movements on its own, like we do when we look around with our eyes."

When satellites move to adjust the direction of standard antennas, they create inertial forces that throw off the orientation of the entire satellite. An adjustable antenna with actuators made of plastic and piezoceramic material would be light enough to generate very little inertia. "That's one of the significant benefits--the satellite wouldn't have to constantly reorient itself. Plus, instead of having three or four antennas on a satellite, we could have one or two multifunctional antennas."

Designing antennas so they can change shape solves certain problems. For instance, sunlight heats antenna materials and warps them. When that happens, adjustable antennas simply would be able to self-correct.

Another common problem is that Earth's atmosphere scatters satellite signals the same way water scatters a beam of light. For this reason, not all transmitted information reaches a target. Standard antennas can't correct for that, but an adjustable antenna could even navigate signals through turbulent atmospheric conditions like storms. It could deliver more information using the same amount of power.