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Saturday
Jun262010

Hey, Hold the Phone!! (Like this...)

Photo by Steve Golson

I hit a nerve on Friday.  

The iPhone 4 antenna controversy was way bigger than I realized. The traffic to this site was incredible, and the extent of the blogs and news sites that picked up my comments was humbling.  I also did four telephone interviews, including the Wall Street Journal - they asked for photos, so we had some fun.  And yes, I did call it the "Vulcan iPhone Pinch".  And no, Leonard Nimoy has not called.

I received many emails, too.  The overwhelming tone of the email was very friendly; I wish I could respond to all of them immediately, but I am afraid that will have to wait.  I will try to touch on the topics raised in some of the emails in this blog entry.

First off, I still don't have my iPhone 4 yet.  Sigh.  I am waiting patiently, so keep in mind that all my comments are based upon my experience with designing embedded antennas, and not with the specific antennas in question.  I promise to post my first-hand experiences here once mine arrives.  Also, I don't have any Apple-specific information that you don't have access to.  I am not a consultant to Apple, and have never been; I don't even play one on TV.  I don't have an axe to grind.  Nor an iPhone 4 to play with.  But, I digress...

I have seen mention of the electrical tape fix, the scotch tape fix, the bumper case fix, even the short-the-other slot fix on various web sites.  The important thing to realize is that we are dealing with radio frequency (RF) currents in the antenna, not direct current (DC) as you will find in a flashlight, for example.  If you place a thin insulator (tape) across the "gap" and over the "band" on the iPhone 4, I would not expect that to make a very big difference.  With such a thin insulator you are effectively preventing a short at DC (zero Hertz), but at the RF frequencies involved (around 1GHz, or one billion Hertz) you are just making a large capacitor.  A capacitor is fundamentally two conducting plates separated by an insulator.  When the capacitance is high enough (plates big, insulator thin) at the frequencies in question, it looks just like a short circuit.  So, I would not expect tape to create any improvement when the Grip Of Death is used (see photo).

When I was on the phone with the WSJ, I explained the two distinct effects that holding the phone over the antennas will impart: detuning and attenuation.  

Detuning can be understood by imagining a wine glass that is empty.  If we tap the glass with a fork, the glass will ring, or resonate, at some frequency.  If we put some wine in it (or apple cider, since I don't imbibe) the resonant frequency will change and in this case increase.  This is the same for antennas.  Antennas are generally resonant at their frequencies of operation, and when we put our hand over them we "load" them with the dielectric of our bag of salty water.  This lowers the resonant frequency of the antenna and may make it harder to squirt energy into it at the frequency we want.  If the antenna is particularly narrow-band, it may "kill" it completely.  Generally, physically small (compared to a wavelength) antennas are narrow-band and large antennas may be wide-band.  This is why detuning is the first detrimental effect of putting your hand on an antenna.  Any antenna.

The second effect is attenuation, or loss.  Your hand is a dielectric, meaning it concentrates electric fields more than air.  This factor is called the dielectric constant, and for your hand is pretty high, like 12 or 20 or so.  It depends on your diet and BMI, so it's kind of personal and I don't want to make anyone uncomfortable by dwelling on it; the important thing is to be healthy.  Oh... right.... so this is what detunes the antenna.  But, your hand is also conductive, but not perfectly so.  So you WILL get a shock if you stick your thumb in a light socket, and I don't recommend it.  This not-so-perfect conductor is what we call "lossy".  RF energy impinging upon your hand (or head) is partially going to be turned into heat.  This is the SAR we were talking about, and you may have heard of.  This leads to an attenuation (reduction) in the signal being radiated into space by the antenna.  This is the other bad thing that happens to hand-wrapped antennas.  Once turned to heat, the RF energy is gone.  Just ask your dinner in the microwave.

So, detuning causes problems with squeezing energy from the circuitry into the antenna (or vice versa), and attenuation causes problems with losing energy to heat.

The so-called bumper case is a much thicker insulator (or dielectric) than a piece of tape. It pushes the lossy dielectric (your hand) further away, significantly reducing the capacitance.  I would expect this to reduce the detuning effect, but not the attenuating effect.  Will it help?  You betcha'.  However, it is a tradeoff: pushing a very high dielectric constant but lossy material away, and substituting it with a lower dielectric constant material.  If I were a betting man, I would guess that the dielectric constant of the materials used is about 3.3.  So, it still will load the antenna, but not as much; and it is entirely possible that this was taken into consideration in the design of the antenna.  Since I have had a case on my Primordial iPhone since it was new, I expect to do the same with the iPhone 4.  When it gets here.  Any time now.

Now I want to rant a bit about the "experimental method" people have been using.  The iPhone 4 was out for roughly 24 hours before people were publishing the results of "tests" proving that it had inferior performance.  At my company, when I get to hook my fancy laboratory gear up to my client's equipment in very controlled circumstances I can't do it that fast.  Folks, there are a couple of reasons that you need to give this product some time before jumping to conclusions.  

First, we have no earthly idea what those little bars in the upper left corner of our screen really represent, yet we are staring at them like they're going to help us find out what those damn numbers on LOST meant.  Steve Gibson of Gibson Research (grc.com) did a great piece on the meaning of the signal bars; I am a huge fan of his, and his measured approach to technical challenges are worthy of our respect.  We don't know what the bars mean, beyond more is better and less is ... less better.  We also don't have a handle on the time constant of the bars, which is to say we don't know when the bars change with respect to when the signal changes.  And worse, we don't know if it's consistent.  After all, it's controlled by software.

Secondly, the cellular system is composed of many cell sites.  While you are making observations, you have no idea whether your iPhone is staying on one cell site, or switching between several.  This will completely obfuscate any measurements, even if you decided that the bars are useful.  In the good old days, when cell phones worked on steam, there was usually a service screen you can hack your way to which would show which site you're on, and how strong it was in real engineering terms (dBm).  I have never seen that capability on the iPhone (but, I didn't look too hard).  Such a capability would be hugely helpful in our experiments.

So, how do we evaluate the performance with these limitations?  The answer is: over more time, in more situations.  You need to observe more bars in more places.  (I know, cheap shot.)  Give it a couple of weeks.  Use it like you used your last phone.  If it doesn't make you happy, return it to Apple.  But, give it a chance, and 24 hours ain't it.

Several reporters wrote that I "blame the FCC for the iPhone antenna problems."  Well, I did say "it's the FCC's fault", but I was a bit glib.  It's the whole process that drives the design (I did say that, too), and part of that process is the tests the phones must pass.  And the FCC could care less whether your phone drops your calls in the middle of a conversation or not; they care about protecting the "spectrum" and safety.  AT&T does care about efficiency, but they assume your hand is made of styrofoam.  Apple cares about striking a balance between product coolness (you'll buy it) and product efficacy (you'll keep it).  All of these pressures lead a product to the end point.  And then the unpredictable takes over anyway, so enjoy the ride.

So, why didn't Apple do it differently?  That's a question I thought about through several showers.  I have finally boiled it down to one thing: any performance improvement would have made the iPhone 4 bigger.  Period.  Apple is putting ten pounds of stuff in a five-pound bag.  Put air space around the antenna to make it less sensitive to the presence of the human hand?  Fuggetaboutit.  Air doesn't sell phones.  Gyroscopes, accelerometers, high resolution screens, multiple cellular carrier capability (did I say that?), and big batteries.... that's what the people want.  

You just gotta hold it like this.