Research Stories

by Joe Kullman

The Electromagnetic Anechoic Chamber. It doesn't sound like a place you would choose to enter voluntarily. But for Constantine Balanis, it's the ultimate playroom.

The chamber is filled with sophisticated instrumentation. Everything is carefully set up to quantify and analyze the way electromagnetic waves behave— or can be made to behave— under varying conditions. Experiments in the dark chamber shed light on the workings of electromagnetic waves.

The anechoic chamber is a toolbox of sorts, says Balanis, a Regents Professor of electrical engineering at Arizona State University. Work by Balanis and his colleagues is brightening the prospects for building the best of all possible antenna systems.

Inside the chamber, the ceiling is 18 feet high. The room itself is 51 feet by 24 feet in size. Much of the floor, ceiling, and walls are covered with hard, black, spike-shaped, foam-like material.

The material is important. It absorbs impinging waves carrying electromagnetic energy. That reduces echoes, or "wave reflections." The reflections would interfere with the precise signal transmissions necessary to test antenna technologies. The room is an "anti-echo" chamber.

At one end of the room stands a 12-foot-high reflective surface. The curved piece of polished aluminum has jagged edges. Balanis bounces electromagnetic waves off this reflector. He aims the waves at small-scale replicas of helicopters, jets, and other targets.

The chamber apparatus is designed to simulate the environment of outdoor communications systems. Antennas are normally separated by large distances. The engineers have devised methods to re-create such conditions inside a closed room. Waves radiated by the transmitting system are first bounced off the curved reflector. They are then directed toward the receiver system being tested.

The curve of the reflector is usually set in a particular parabolic shape. This allows the researchers to transform spherically shaped waves emanated from the transmitter into planar (flat) waves. The flat waves are bounced from the surface of the reflector and directed toward a signal-receiving system.

The reflector in the anechoic chamber is curved in one direction and flat in the other. As a result, it creates cylindrical-shaped waves. Balanis and his colleagues need the help of special computer software. The programs compute the conversion of the cylindrical wave illumination of the receiver. The engineers can then see what it would be like if it were illuminated by a planar-shaped wave front.

"We want it to be a planar wave," Balanis explains. "In actual outdoor conditions the transmitter and receiver are separated by long distances. Waves from the transmitter impinging on the receiver are nearly flat. To simulate outdoor wave fronts we must create similar ones indoors."

ASU's anechoic chamber is a multipurpose antenna research facility. Engineers can use it to measure the performance of complete, extensive beam-formed "smart" antenna systems. But Balanis also uses it to measure the wave-scattering characteristics of radar targets. His research is part of almost two decades of work on the development and advancement of stealth technology.

Experiments conducted in the chamber are one aspect of broader research to improve both the hardware and computer software of antenna systems technology. Balanis says that advances will expand capabilities to integrate or reconfigure multiple-access wireless communications networks.

What does all that mean?

Better "smart antenna" systems will vastly improve the quality and reliability of Internet and telephone connections. All wired and wireless communications systems will benefit. That includes cell phones, local area networks, and WIFIs, says Christos Christodoulou, an electrical engineering professor at the University of New Mexico who collaborates with Balanis.

"There will be less noise and fewer interfering signals from other users of such services. You will be able to take your wireless laptop computer much farther away from its connecting base without losing connectivity," Christodoulou says.

"Smart antennas also have the capability to reduce signal fading, which causes calls or connections to be dropped," he explains. Fading occurs when signals get bounced off buildings and other structures. The buildings interfere with a signal meant to reach a user directly.

Balanis says that smarter antenna systems will overcome many obstacles. They will deal with tall buildings, long distances, and the ever-proliferating number of communications networks crowding the airwaves.

Read more about Balanis' antenna research in "Antenna brainiacs."