Monday, October 10, 2011

Gizmodo Explains: What’s So Smart About the iPhone 4S’s Antenna?

With the iPhone 4S, Apple says it will deliver an iPhone that works anywhere in the world, and with fantastic reception.

How did they do it? One word: antennas.

Apple’s marketing guru Phil Schiller said the iPhone 4S “intelligently switches between two antennas to receive and send.” Brilliant! But vague. How exactly does a smart antenna act?

When you have a small, thin device that needs to receive and send multiple types of signals without interfering with one another, you need to get creative. As we learned from the iPhone 4 “antennagate,” even the best engineers and designers can’t always come up with perfect antenna scheme.

But antenna gurus have plenty of tricks up their sleeves, it’s just a matter of finding the best recipe—and sometimes inventing a spanking new technology.

“What [Apple] seemed to allude to was a switching or selective processing technique: taking the better signal between two antennas and using it,” said Aaron Vronko, co-founder of Rapid Repair, in Portage, Michigan.

That’s one step in the right direction, but there are many other antenna hurdles to clear. On a cell phone, antennas have to be placed close together simply because cell phones are little. And antennas close together tend to interfere with each other. One way phone makers can address that is by placing antennas at opposite ends of the phone, a technique called spatial diversity.
In the AT&T version of the iPhone 4, however, both cell antennas were at the bottom. So if you happened to grab the phone too close to both of them simultaneously, you would experience signal attenuation. Antennagate!

But Verizon requires that the antennas on their phones be separated at the top and bottom of the device. That way, if you’re holding the phone at the bottom, you likely have a free antenna at the top.

Still, since a cell phone is so small, simply separating the antennas won’t prevent all interference. You need a space between them of at least one full wavelength. At the lowest wavelength, about 900 MHz, that would be 13 inches. Not even Gordon Gekko’s phone was quite that big (his DynaTAC was 9.8 inches). So engineers use other “antenna diversity” approaches, like polarity—placing the antennas at varying angles, or pattern diversity—using antennas with different radiation patterns.          More