Apple's Antenna Problem Is Different

Apple's Antenna Problem Is Different

Apple admits that the external design of its antenna reveals an "attenuation weak spot" not present on other smartphones.

Apple's Antenna Problem Is Different


In his explanation of the iPhone 4's antenna problem on Friday, Apple CEO Steve Jobs used a slideshow to argue that other popular smartphones face the same reception problem when held the wrong way. Apple then posted videos of several smartphones, including the iPhone 4, suffering diminished signal strength when gripped in certain ways.

The point of these exercises was to demonstrate that the iPhone 4's antenna issue is not unique among cellphones. However, it is. itself makes it clear that the iPhone 4's antenna issue differs from general interference faced by other smartphones, including previous iPhones, all of which have an internal antenna. The design difference between the iPhone 4 and other smartphones is plain to see: It allows a finger to bridge the antenna's feed point, altering the antenna's characteristics. That does not happen with an internal antenna, regardless of what Jobs tried to imply on Friday.

"The external antenna on iPhone 4 is located in the stainless steel band," reads the caption under a photo indicating where the problem exists on Apple's page (image to the right). "The attenuation weak spot is the black strip in the lower left corner of the band." For all of the other smartphones on that page, the corresponding captions describing grip-related interference refer to the "location of internal antenna" or "main internal antenna," rather than to an "attenuation weak spot."

Experts agree that the iPhone's problem is different from that faced by other phones, regardless of Jobs' protestations to the contrary.

Joe Banos – antenna expert, electrical engineer and COO of Wilson Electronics, which makes cellphone signal boosters for the car and the home – explained how the iPhone 4's antenna issue differs from those of the other smartphones listed on Apple's comparison page. Banos has nothing against Apple or AT&T, and would in fact like his company to partner with them one day, and he insisted that we make it clear that he has not even used the iPhone 4. However, its problem is so obvious from an antenna engineering standpoint that he didn't need to hold it in his hand to see where its design went wrong.

The iPhone 4 antenna's feed point, located at the plastic strip separating the metal of the antenna, can be bridged by a human finger, which changes the capacitance of the antenna, causing an impedance mismatch that reduces the signal, which is why the problem affecting Apple's external antenna does not affect the other phones listed on Apple's comparison page.

"Any time you touch the feed point, it's kind of like squeezing the jugular vein on your neck, like the 'Vulcan hold' from Star Trek," said Banos. "Apple says all phones have this problem – yeah, they have that problem after you fix the problem with touching the antenna."

He laid out the difference between the issue affecting the iPhone 4 and the one affecting phones in general as follows:

Absorption (happens with all cellphones): Electromagnetic waves, such as radio frequency (RF) waves, penetrate materials differently based on their characteristics. Any time you wrap your hand around an antenna, the human tissue around is going to absorb some of the waves. "It's just the laws of physics," explained Banos.

Impedance Mismatch (happens with iPhone 4): Any antenna at any frequency made out of any metal has a specific characteristic, called impedance, and the engineer's challenge is to match the impedance of the antenna to the impedance of the transmitter and receiver inside the phone. "When you physically touch the antenna in that spot, you're changing the impedance characteristics of the antenna," said Banos. "You're causing a mismatch – nothing to do with absorption."

Banos points out that the bumper Apple supplies to solve the problem is not thick enough to have a measurable effect on any absorption problem encountered by the iPhone 4. It's beneficial effect is purely a result of the way it prevents one's finger from touching the antenna's feed point, solving the impedance mismatch issue.

It may seem as if we're belaboring the point here, but it takes some work to clear up the confusion Apple is spreading about cellphone antennas. In some places, the company implies that the impedance mismatch problem and the absorption problem are one and the same. In others, the company acknowledges that a difference exists – for instance, with the phrase "attenuation weak spot" only being used to reference the iPhone.

Nonetheless, Jobs said, "This is life in smartphone world," ignoring the difference between the absorption and impedance mismatch problems. "Most every smartphone we tested behaved like this... The heart of the problem is that smartphones have weak spots," he added, conceding, at least, that Apple "made it very visible."

According to Jobs, the iPhone 4 suffers from a problem that affects all phones; it just happens to be more "visible" on the iPhone 4, which isn't really a big deal. But if other manufacturers were experiencing this problem, they too would issue free antenna covers. They are not doing so.

"Apple's attempt to draw RIM into Apple's self-made debacle is unacceptable," said RIM chief executives Mike Lazaridis and Jim Balsillie said in a Friday statement. "Apple's claims about RIM products appear to be deliberate attempts to distort the public's understanding of an antenna design issue and to deflect attention from Apple's difficult situation."

Nokia also took a dig at Apple. "As you would expect from a company focused on people, we prioritize antenna performance over physical design if they are ever in conflict," said the company, implying that Jobs' designers ignored customers' needs by prioritizing physical design over antenna performance.

It's hardly surprising that Nokia and RIM would bristle at Jobs' attempt to conflate iPhone 4-related problems with those of cellphones in general. After all, Apple itself admits, however circuitously, to a noteworthy distinction between an internal antenna, whose signal can be blocked by vague obstructions, and an external antenna that loses signal power when a finger touches its "attenuation weak spot."

Apple has not published any data that would allow independent review of its explanation.

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