Lee Center for Advanced Networking

“Wireless communication is tough,” says David Rutledge, Lee Center director. “After all, you are just throwing the radio waves out there.” Outsiders may intercept a signal, creating security problems; other electromagnetic signals may interfere with the main signal; and, finally, radio waves become weaker with distance, just as light and sound do. The solution to this last problem is to use higher-frequency signals.

Until recently, higher frequencies in the electromagnetic spectrum were reserved for government uses, but these high-frequency wavelengths are now becoming available for commercial applications. Higher frequencies give greater bandwidth, which equals faster transmission—so voice, text, pictures, and video can move quickly, smoothly, and reliably.

Unfortunately, using higher frequencies creates some problems. For example, because of the way transistors work, higher frequency systems require more power. A transistor amplifies a signal or opens or closes a circuit. But as the frequency of a signal increases, the power output of a transistor drops dramatically. When you go to a higher frequency, he says, “you have to come up with a way to combine the power output from lots of transistors—hundreds or thousands—to get the power that you need.”

In his research on antennas, Rutledge found a way around the transistor problem. Rutledge and his colleagues are developing an “active antenna” that aggressively pulls a signal in, then just as aggressively sends it out. The active antenna works by using large numbers of transistors.

Normally, transistors are laid down across a chip in a single, long row, linked by a metal transmission line. But the longer the line, the more power is lost. To avoid long, power-dissipating lines, Rutledge and his colleagues laid out the transistors in a grid pattern, so the transistors are connected only by short wires. In a receiving antenna, the power of an incoming signal is divided among all the transistors, which, combined, act as one giant antenna and pick up the signal without losing power.