Discriminating ‘Smart Antennas’ Signal a Clear Advantage in a Patch
Despite all the progress in consumer electronics, the antenna on my cell phone still looks a lot like the one on my 20-year-old CB unit.
Unfortunately, neither works as well as it should.
Now, lurking just around the corner is a new generation of antennas that promises to radically improve wireless communications. The basic idea behind the technology is really quite simple: If two heads are better than one, then two or more antennas should also be better than one.
The technology has been in the developmental stage for more than 25 years, mostly by the military, which called it “adaptive antenna arrays.” That’s not jazzy enough for the age of e-commerce, and the concept has morphed into something called “smart antennas.”
Both terms mean the same thing. More than one antenna provides the ability to reduce background noise and interference, and a smart antenna should also be able to discriminate between the signals coming from various sources, as when a cell-phone user is being “handed off” from one cell to another.
Smart antennas are already in the advanced stage of development by such giants as Texas Instruments and Bell Labs, and they are expected to start showing up on consumer devices in the near future. But don’t look for two or more “whip” antennas sticking out of your cell phone or laptop. You probably won’t even know these antennas are there.
That’s because antennas themselves are changing. Instead of a whip, the new antenna will look more like a printed circuit. Called microstrip patches, these antennas can hide inside a device and are expected to be much cheaper to mass produce than conventional antennas.
It’s the antenna of the future, said Michael Zoltowski, professor of electrical engineering at Purdue University. “That’s pretty clear,” he said.
Zoltowski has spent years developing smart antenna systems for the military that will protect the Global Positioning System from being jammed by unfriendly forces. Working with the Polytechnic University of Madrid, Zoltowski, a signal processing expert, came up with an array of six antennas that allows a GPS receiver to reject up to five jamming signals.
Similar technology is under development for a wide range of uses, including satellite television receivers. Choon Sae Lee, associate professor of electrical engineering at Southern Methodist University in Dallas, has developed a 10-inch-square microstrip antenna that he says does just as good a job as a satellite dish, and costs far less to produce.
The antenna, which can be mass produced with no need for assembly, like traditional dishes, is about to go into production at Crest International in Fort Worth.
Satellite dishes are the largest segment of the consumer electronics business in the United States, according to Crest President Tom Athans, who hopes to capture half of that market.
For hand-held devices, such as cell phones or even laptops, two or more antennas provide a clear advantage over a single antenna.
“Having two antennas allows the cell phone to be directional,” Zoltowski said. “It’s similar to our ears. We have two ears, and we can get some indication of which direction a sound is coming from.”
That would allow the cell phone to select a signal coming from the direction of a base station, instead of one bouncing off a nearby building, for example. It should also make it easier to switch from one base station to another when passing into a different cell, because the phone would be able to discriminate between the two signals and select the new station.
It would be even better if the phone could suppress all reflected signals, like those bouncing off numerous buildings in an urban environment, but that gets very complicated. Bell Labs has made some progress in that area by combining signals from several antennas to reduce noise and interference, giving more weight to stronger signals and minimizing weaker signals.
The system worked, according to a lab report, even when cell phone users in adjacent vehicles were transmitting on the same channel. That would have been impossible with a traditional antenna because of interference between the two phones, the report said.
But more antennas means more signal processing equipment inside the device, and that adds weight and reduces battery life.
So Lucent Technologies is experimenting with a wireless laptop that will have up to eight antennas, but only four processing units. The laptop will select only four antennas, the ones receiving the strongest signals, thus eliminating the need for eight processors.
The system is designed to hop from one antenna to the next, picking the four that are most effective at any given time.
Zoltowski sees the day when our wireless devices won’t have any visible antennas because microstrip patches will be embedded inside. But that will take a little getting used to.
He said one manufacturer had experimented with that already.
“But the funny thing is, people expect to see that antenna there, and they were having problems with buyers,” Zoltowski said. “People were bringing them back saying, ‘I don’t have an antenna.’ ”
*
Lee Dye can be reached at leedye@gci.net.
