Archive for June, 2010

The Real Issue Behind The iPhone 4 Antenna

When the iPhone 4 was first announced, I was pretty amazed at the design. I especially thought it was quite neat that the antenna was built into the frame of the phone.

Then they said that the frame was exposed, and that’s when my admiration stopped.

Seeing the launch and the fact that the frame was uninsulated metal (and hence requiring black bands on the sides to insulate the two antennas from each other) was a bit of a “hmmmmmmm…” moment.

I didn’t think much at the time of the ramifications. My area of work specialises in amplification and digital signal processing, not analogue transmission. The two thoughts that immediately came to my head was that one, it was going to have zero reception if the iPhone was in your pocket and you had keys touching the insulation band, and that two, surely apple would’ve extensively tested it for such a critical performance measure as phone reception.

Alas, only my first thought was correct. At the time, I didn’t think of the fact that your hands are a fairly good conductor of electricity at the signal level, and if you touched any antenna, even if it was just one antenna, you’re likely to be able to change the parameters slightly.

Moreover, you’d completely alter them if you were shorting a slither of insulation between two metal strips which both act as antennas.

An antenna works on a number of key parameters, including gain, resonant frequency, impedance and bandwidth. The antenna on the iPhone would have a certain set of these characteristics which is attributed to its length, thickness, shape and material. Changing any of these physical features will alter the electromagnetic characteristics of the antenna. (At the risk of showing my age, if you’ve ever used an indoor TV aerial, you would’ve noticed that touching the metal bits changes the reception.) If you connect two of these antennas together, nearly all of the above parameters will change, not to mention the possibly of interference between the two signals.

But that’s exactly what happens when you touch the black strip. Your fingers are reasonably good conductors, and since the strip is so thin, it’s likely that there will be significant electrical connection between the two metal parts, especially if your fingers are sweaty. Moisture on our skin act as great contact material due to its salt content. Plus, most of us who are alive also tend to be full of water and salt, which makes us good conductors (this is why we can get electrocuted, and it’s also how lie detectors work – they detect the resistance on your skin to test for how much you’re perspiring).

Users have reported that their reception drops when holding it in a particular way. Many online “experts” have falsely attributed this as a software problem, a bug, or a host of other issues clearly spoken by those who are more at home on facebook than in a lab. Let me tell you: it’s a design flaw. It’s a major, fundamental, “newbie” design flaw and I can’t believe a company like Apple could have not tested it properly.

I’ve always been an admirer of Apple. I’m not a fan of their business model, but the way they have designed and tested their products hitherto has been the key to their success. Their triumph of form supporting function is what has set them apart from their competitors. Is this the start of their downfall? Probably not for now, but given their ridiculously intensive product release timelines, it’s not surprising that these basic design problems are creeping up.

In any case, it brings me to my main point: Apple completely botched it up. And it just goes to show that even big companies make totally trivial mistakes. Apple would’ve had the design going for a number of years, and probably tested it for months before release. Yet such a fundamental problem was noticed by a lousy electronic engineer who saw a 5 minute video of the product launch.

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