A Bit Off Base: The science behind the iPhone 4's antennas


There’s a problem with the iPhone 4 antennas which limits their effectiveness. Many people point to this article by Spencer Webb who seems to be (and I know nothing different) to be an antenna expert to explain why there’s a problem, but he’s a bit off base.

The problem with the antennas, as he points out pretty clearly in his article, is that two of the iPhone 4’s metal frame pieces are pretty-well shorted out when you smoosh your palm over the slot between them. To quote:

If you short these slots, or cover them with your hand, the antenna performance will suffer…

I think, judging by the remainder of his discussion, that he somehow thinks the slot is responsible for the miraculous improvement in antenna performance vs. the 3G or 3GS. Either that, or he is just drawing the wrong conclusion from the videos and his own experiments, because he spends the rest of the article discussing the antenna location, the FCC, radiation into the body, attenuation by body parts, and other good (and true) stuff. But he seems to forget the whole “antenna is shorted out” problem.

So here’s what I think, and why. Let’s start with what we know:

It is my contention that the degradation of antenna performance is simply the direct result of shorting the antenna to its reference ground plane.

The problem here is that both Spencer and everybody else on the web seem to be blaming the fact that sticking your hand in the way of the antenna is somehow responsible for the performance degradation. Though there certainly may be something to that assertion, it is most likely a minor cause of performance degradation.

Here’s what I did to confirm my conclusion. Holding the phone using the prescribed iPhone 4 Vulcan Grip, I noted that I had three bars in the basement of my house. When I licked my pinky and moved it upward to cover the slot so it was touching both metal frame components on the left of the phone, the bars went away, slowly, but surely. I didn’t introduce any large portion of my body (yeah, I’m 6’6” tall and have big hands, but not that big!) into the radiation pattern of the phone, and yet the signal all but went away.

So I’ll make you a bet (nothing’s riding on the bet, sorry): if you cover the left portion of the metal frame or the bottom portion of the metal frame with electrical tape, the problem will go entirely away. I’m not totally sure about the involvement of the right portion of the metal frame, because I don’t know if it’s electrically isolated from ground or if it’s another band’s antenna. Maybe you’ll have to cover that one, too.

In any case, I simply can’t believe all of the hype and misinformation here. There is a problem, that’s certain. Using a Bluetooth headset and keeping your phone in your pocket will help it, but for the wrong reasons. Becoming a “righty” might help it just as much. Anyway, at some point in the future, I’ll call Apple and complain a bit about the phone’s reception and see if I can get mine replaced with one that may have some protective coating applied wherever it should have been. But in the meantime, I’ll just use the iPhone 4 Vulcan Grip and will still be just as pleased with the amazing piece of technology resting between my fingers.

I’m an electrical engineer by trade, but not an antenna expert. The knowledge I’m relying on here, though, is sophomore physics class-type stuff, and is not rocket science.

Recent Comments