Electronic Design
Apple Feels Antenna Angst As Form Trumps Function

Apple Feels Antenna Angst As Form Trumps Function

As you’ve probably heard, Apple’s new iPhone 4 has an antenna problem. The metal band holding the two thin glass panels that make up the housing serves as the main antenna for the phone. If you hold the phone in a certain way, now known as the “death grip,” the signal is attenuated and dropped calls are likely. The thin black insulating strip at the bottom left of the phone is the weak point. If you “short” that out with your hand or finger, you will significantly reduce the antenna effectiveness.

It’s hard to say just how big a problem this is with current users, but it has generated many complaints. The biggest concern Apple has is that word of this defect could hurt sales. So far, the company does not seem to be losing that many sales, but who knows? Consumer Reports issued a statement saying that it could not recommend the iPhone 4. That’s not good.

Some people have said that a recall of the phone is possible, but that does not seem to be what Apple really has in mind. At a press conference on Friday, Apple admitted the problem and offered to give iPhone 4 owners an insulated case that effectively solves it (see “Jobs Refutes iPhone 4 “Antennagate” Hype,”). Some users have also solved the problem by putting a piece of tape over the black insulator. Ah, another unexpected use for duct tape. Latex gloves probably work too.

How about a Bluetooth headset? With the iPhone in a case on your belt and the Bluetooth headset in your ear, I suspect it would work just fine.

Apple also has admitted that the software controlling the signal level bars is out of whack. The bars apparently do not provide the real story about signal level, possibly accounting for some of the problem. I suspect that this aside is just a mental trick to make users think things are better than they are. Maybe I’m wrong about that.

But I suspect that when this level of money and image are involved, a company will say anything to make things seem better. None of those bar displays are very accurate anyway. They simply offer a relative indication of signal as produced by a typically not-so-accurate received signal strength indicator (RSSI) reading from the receiver. It’s better than nothing, but don’t count on 100% accuracy. RF is too fickle.

When I first heard of this problem, I had to say, well, didn’t an antenna engineer design this piece? The answer is yes. But reports say that when Apple’s antenna guy complained that it was a bad electrical design, the packaging design guys overruled him, probably Steve Jobs himself. In the Apple tradition, style and physical design are everything, and Apple has been very successful over the years with this approach. I suppose it had to come back to bite Apple at some point. In any case, form beat function for a bad outcome.

The Perils Of Antenna Design
Anyway, as an RF person myself with lots of hands-on antenna design experience, I can tell you that touching an antenna is a really bad thing. This is especially true of antennas that operate in the 800-MHz to 1.9-GHz range. Just getting near an antenna will distort its radiation pattern and reduce its efficiency. Touching one is almost as bad as disconnecting it. Cell-phone designers have had difficulties from the very beginning in putting an antenna inside the case.

Remember those extendable whip antennas on early cell phones? They were troublesome and ugly, but they worked. Now antennas are all inside as new designs have come into being. But putting that antenna near your hand and head really attenuates the signal and changes its radiation pattern significantly. Antennas are designed to account for this, but it doesn’t include physically making contact with the conductors. I’m actually amazed that the iPhone 4 antenna works at all with someone touching it.

I was reminded of this problem as I was developing some lab experiments for a college wireless class recently. I used 915-MHz industrial-scientific-medical (ISM) band transceivers with half-wave vertical antennas. They work fine, but getting within a few inches of the antenna really messes up the transmission.

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In trying to plot different antenna patterns, I found it difficult to get reasonable results because just being near the receiver or transmitter antenna disturbed the signal strength and plot. That’s why commercial antenna tests are run in shielded rooms with lots of isolation and remote metering of results. Close proximity to an antenna is bad, so you can imagine what full contact will do to the signal.

The whole antenna situation with cell phones is a massive challenge to designers. There are multiple antennas in all cell phones these days, usually two for quad-band phones, with one for the Bluetooth, one for the Wi-Fi, and another for the GPS. Being jammed in there close together means that all these antennas influence each other, lowering the efficiency of all of them. Just wait until we get Long-Term Evolution (LTE) multiple-input multiple-output (MIMO) in the handset. It’s on the way. It will only be 2x1 MIMO, but even that will cause additional problems.

Antennas are basically nothing more than little bent pieces of metal. But lots of thought, math, testing, and experimentation go into making them work. And you have to have a good antenna. They are the transducer to the “ether” that makes wireless work. Antenna design is truly a black art, despite the good modeling tools available today. Smart phones have really put the pressure on designers dealing with both the antenna and packaging.

The lesson here is to listen closely to your RF/antenna guy. Now you know why that “fields” course that you had in EE school, where you tried to learn Maxwell’s equations, was important.

The iPhone is probably the best smart phone out there. I’ve had two of them. My 3GS is so good I don’t really need an iPhone 4, which is easy to criticize. Apple has done a remarkable design job over all. Any RF product, especially one this complex, is going to have some issues. It’s hard to be perfect in any design. But this antenna problem could have been averted.

I can’t wait to see what Apple does with the iPhone 5 antenna. An aluminum foil hat would be good.

TAGS: Components
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