by Joe Kullman

Constantine Balanis is an innovator. The technological strides he makes are large. How big? Consider the following analogy as an illustration.

Imagine two people talking. They walk inside a room so darkened that they cannot see each other.

Each can determine the location of the other as they move around the room because the voice of the speaker arrives at the acoustic sensors —the ears—of the listener at slightly different times.

The brain is a human signal processor. It calculates the difference in the time delay of the sound of the speaker’s voice received by each ear and then computes the direction of the speaker.

Such abilities also allow the two to carry on their conversation even if additional speakers enter the room. They can effectively tune out the unwanted interference. They focus on the transmission and reception of the sound of each other’s voice.

Balanis is trying to make electrical antenna systems smart enough to do the same thing. Balanis is a Regents’ Professor of electrical engineering at Arizona State University’s Ira A. Fulton School of Engineering. He has spent decades working to coax better transmission and reception efficiency from antenna technology.

In the ASU researcher’s world, the ears are antennas and the brains are digital signal processors. The signal processors are what measure time delays between various elements of radio signals. The processors then compute the direction of arrival of the signal. They “adjust the detections” (the strengths and phases of the signals). This allows the antenna elements to focus on specific signals while tuning out others.

Electrical signals are “complex” quantities. They are represented mathematically by amplitudes and phases, Balanis explains. When electromagnetic waves travel over distances, their amplitude (strength) can change for different reasons. Attenuation (a reduction in strength) is one cause. Diffusion—the spreading of waves—is another. Phase changes due to the speed of the wave and the distance it travels can also affect amplitude.

The ASU engineer’s goal is to provide stronger and more accurate transmission and reception. That would expand the range and capacity of such systems.

Balanis says that such advances will propel the evolution of wireless communications. Improvements in “smart” antenna systems will help cell phones, aircraft, satellites, ships, automobiles and laptop computers to perform more effectively.

But pushing the envelope on antenna technology depends on advances in myriad facets of science and technology.

“In developing an advanced antenna system, researchers pursue two parallel paths,” says Magdy Iskander, director of the Hawaii Center for Advanced Communications in the College of Engineering at the University of Hawaii at Manoa. “One path involves the antenna array design. This includes types of antennas, array configuration, the number of antenna elements, and their geometrical arrangements.”

The other path involves the development of algorithms, he adds. Such problem-solving computer programs would process received signals from the antenna array elements and help to optimize a system’s performance.

New hardware is also being developed. Scientists and engineers are studying new materials or composites of new and old materials that might enhance antenna systems. What the hardware is made of can affect a system’s overall performance. So can the design of each antenna component and the proximity of each component to the other, right down to the tiniest circuitry.

There is also the matter of antenna array geometry. Engineers must figure out the optimal geometrical arrangements of antenna system elements. The goal is to provide the best possible transmission power and reliability.

Beyond the physical pieces to the puzzle are the invisible aspects of antenna systems research. Balanis says that requires unlocking remaining mysteries about the workings of electromagnetism.

Building the next generation of antenna systems is complicated. It is really about the ability to more precisely measure and manipulate the amplitude and phases of electromagnetic waves.

To do that, Balanis and others are experimenting with how to shape the patterns of such waves as they are radiated outward or received inwardly. This may be one way to get antenna systems to do more precisely what two humans can do while conversing in a dark room. The key is to filter out interference from other voices and focus on the sound of the voice they want to hear.

The development of better algorithms and implementation procedures for “smart” antennas is essential,” Iskander says.

Researchers explore “adaptive beam-forming,” or “beam-shaping.” They want to enable an antenna system to block out interference or unwanted signals by “steering” most of the electromagnetic wave energy in desired directions. At the same time they must suppress wave energy in the direction of “interferers.”

For example, think about how the government version of the Global Positioning System (GPS) works. To function correctly, Balanis says, the system needs to select the signal from the user while suppressing all the other unwanted signals (interferers) that exist in the airwaves.

But the signal strength from the interferers is often stronger than the signal from the user. To compensate, the GPS system must have the ability to suppress the interferers even if their signal strength is more intense, Balanis explains.

Christos Christodoulou expands on the concept. He is an engineering professor at the University of New Mexico and one of Balanis’ longtime research colleagues.

Think about cellular phone networks, he says. The quality of service in such a network can be improved with better antennas. Christodoulou says that range of service can be increased by dedicating a certain “beam” of wave energy coming out of an antenna to track a desired “mobile” (a network user or customer).

At the same time, beam-forming prevents interfering signals and electromagnetic noise from getting into the communication channel between two cell phone users.

The key is having beams directed in the desired direction, Christodoulou explains. In the cell phone example, that would mean in the direction of a friend who is calling you.

“The sensitivity of the antenna can be increased toward that friend,” he says. “At the same time we can eliminate or reduce any signals that are floating out from all the calls taking place simultaneously in any particular area between many other subscribers.”

The big challenges facing engineers involve devising analytical formulations and associated algorithms for better and faster beam-forming. The algorithms adjust the amplitude and phase excitation of the antenna array elements to produce better beam-forming. As a result, a system’s capabilities to send and receive signals will improve.

The need for advances in the technology is important. Society is relying more and more on its wireless communications devices.

The need for clear, distinct, rapid and dependable transmissions is especially important as urban areas grow. With growth come more and more cell phone networks and other communications systems. More systems mean increased congestion of wave traffic.

The range of new systems also must be improved. Rural regions have less dense population. Base stations are separated by greater distance.

Traffic jams can jumble transportation networks. A tangle of transmissions can disrupt a communication system. Balanis and his colleagues are working on ways to prevent transmissions tangle. They are experimenting with “spatial processing” techniques.
The new techniques would improve multiple-access systems—antenna systems in which different beams can be adapted for different users. They are also studying methods that allow different users to share the same waves.

“You can use the same antenna system infrastructure—in other words, the same transmission base station—for multiple users,” Balanis says. The key is to use multiple antenna elements that are spatially separated.

“You can excite the antenna elements so that the beams are formed in a way that serves different users,” he adds.

The use of multiple antenna elements also ensures more stability for an antenna system. Weak signals get dropped when they fade or get scattered. If a signal is dropped by one or more of the multiple antenna elements in the system, chances are good that the signal will not be dropped by other elements.

“Antenna systems are the voice and the ears of high technology,” Balanis adds. He and his colleagues are working to produce stronger and more accurate “voice” transmissions and “ears” with better reception capability. Such achievements promise to brighten the technological horizon of an ever more thoroughly wireless world.

Antenna system research at ASU is supported by the National Science Foundation, NASA, U.S. Army Research Office, U.S. Office of Naval Research, Boeing Company, United Technologies, Rockwell International, Motorola, IBM, Bell Helicopters, and Trivec-Avant. For more information, contact Constantine Balanis, Ph.D., Department of Electrical Engineering, 480.965.3909. Send email to balanis@asu.edu

Read more about Balanis' work in "Inside the anechoic chamber" and "Improving antenna 'vision.'"