Apple iPhone 4 Reception Problems a Lesson in Antenna Design

 
 
By Wayne Rash  |  Posted 2010-06-28
 
 
 

Apple iPhone 4 Reception Problems a Lesson in Antenna Design


Imagine, if you will, a day when the term "wireless" had a lot to do with Morse code. In those days if you wanted to transmit signals, you had to get a license from your national regulatory authority, which in the United States is the Federal Communications Commission. One of the areas where you had to pass a rigorous test was in antenna design. Since then, things have changed a lot. 

Probably the thing that's changed the most is that people are allowed to operate radio transmitters without a license, which means, among other things, that you don't need to take and pass a test before you can use your WiFi router or your cell phone. But it also means that most people don't really understand how a radio antenna works, or for that matter, what it does. 

iPhone 4: What's All the Hoopla About? Find Out Here

The reason I mention this is the current round of complaints about poor reception with the iPhone 4. Apple's response is to not hold the device so that your fingers cover that thin black band on the lower left of the iPhone 4's outside edge. The reason this causes a reception problem is that this thin black band (and a similar one on the other side of the device) is actually the insulator that separates two antennas, one for the UHF part of AT&T's voice band and the other the microwave 3G, WiFi and GPS signals.  

When you touch this thin black band, you provide an electrical pathway between these two antennas. How much of a pathway you create depends on your personal physiology and the conductivity of your hands. Your hands can change these characteristics when they're wet, and especially if they're sweaty, since perspiration contains salt, which aids in conduction.  

It's part of the basic design of the iPhone 4's antenna that you can affect its reception in this way, but that doesn't translate into saying that it's a bad design. Like the antenna design in every other cell phone, the iPhone 4 design is a compromise. The engineers who designed it had to choose between an efficient antenna that would overcome some of the reception problems that had spurred earlier complaints and some worse reception problems that currently plague other smartphones.  

In most wireless devices these days, the antenna is printed on the main circuit board, or one that's situated next to it. It looks like a copper zig-zag design, and it's usually under the keyboard or the battery, although there are many places where the designers place them in the interests of looks, convenience or sometimes efficiency.  

Antenna Display Fine Engineering, Poor Usability


 

Apple's engineers took an innovative approach to creating antennas with good access to free space, appropriate physical and electrical length for the frequencies required, and a robust physical design. It's much better in many ways from the little wire pull-up antennas that used to plague cell phones. It's also a more efficient design than those zig-zag antennas buried in the innards of most other devices. But it is subject to user interaction. 

But user interaction is a factor in every phone, regardless of maker or design. One way or another, users can find a way to interfere with radio reception regardless of the phone. With the iPhone 4, you can do it by putting your hand on that little black strip. With the Nokia 100 (this goes way back), you could do it by touching that little wire antenna that stuck up from the top.  

At this point, I'm going to totally ruin the day for those iPhone partisans who are just waiting for an excuse to yell at me. When I looked at the interior of the iPhone 4, I was struck by the elegance of the device's antenna design. It was clear from the first glance that there would be an issue with people touching the antenna, but it seemed to me at the time that that risk was worth it given the efficient radiators that those outside strips of metal had become.  

From an engineering viewpoint, the iPhone 4 has a seriously good antenna design. From a usability viewpoint, not so much. Perhaps the inclusion of a thin layer of clear plastic might have helped, or even a sticker with an arrow pointing to the gap and the words, "Don't hold phone here" might have been enough. But once you know that when your hand covers that gap you will get poor reception, then you will know not to do it.  

Given the location of the iPhone 4's antenna, it was a sure thing that the reception would have been affected by being held, if only because the user's hand can change the overall capacitance of the system, and that in turn can affect the efficiency of the antenna. Given the fact that the design overall will result in better reception than if it had been placed internally, it's a net gain. There's really nothing wrong with the iPhone 4's antenna that a little knowledge about antennas won't fix.


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