Giz 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 mobile phone, antennas have to be placed close together simply because mobiles 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 iPhone 4, however, both 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, as a mobile 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 900MHz, that would be 33cm. Not even Gordon Gekko's phone was quite that big (his DynaTAC was 24.8cm). So engineers use other "antenna diversity" approaches, like polarity — placing the antennas at varying angles, or pattern diversity — using antennas with different radiation patterns.

For the iPhone 4S, Apple probably implemented spatial diversity for both incoming and outgoing calls, according to Spencer Webb, CEO of AntennaSys, an antenna design and integration consulting firm. It's yet another an improvement, but it's not enough to get a hardened antenna expert excited.

"I do not think any special magic is going into this design whatsoever," Webb said.

What Webb finds a bit more interesting is imagining how Apple and other mobile phone makers pass the FCC requirements for radiofrequency emissions. All of this antenna switching uses a lot of energy, and all handheld devices have to stay below a specific (and quite conservative, according to Webb) level for transmitting heat to human flesh — and don't forget they have to cram the GPS and Wi-Fi antennas in there too. So to create a device that won't heat up your head (and to prevent excessive battery drain), Webb thinks Apple may have come up with a fancy algorithm for distributing antenna signals — which might be Apple's secret.

If reception with the iPhone 4S works as great at Schiller claims, I might be convinced to upgrade from my iPhone 4. But who are we kidding? The iPhone 4S could require you to carry your own bunny ears around to make the thing work and people would still line up to drop their $799.

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