Well, I really hate to be (possibly) proven right about certain things, but reports are coming out thick and fast about reception problems with the iPhone 4 when held in the hand. Here are just a few examples:
(nice video demonstration)
I called this issue out way back on the 8th of June when the iPhone 4 was first announced and the antenna design revealed in the following thread, which I'll quote from:
As you can see I was sceptical that Apple would be so stupid as to use the frame as an un-insulated antenna. Well, it looks like I was wrong about that, but therefore right about the effects of touching the frame on signal strength.One bit of remaining scepticism for me is the claim of using the casing edge as antennas to improve reception. Although I'm willing to be proven wrong, I think this claim is bogus, just as it was for the previous generation phone where they claimed the ring around the headphone jack, the camera, and the front chrome bezel were used for antennas. (When clearly they were not - they're all loops, and they're not connected to anything...)
First of all, the lengths of the metal are not even close to the correct length for the frequencies they're trying to transmit - they're actually too long for 2100Mhz for example, but the biggest problem of all is the fact that you are touching the supposed antenna when you hold the device. Any RF engineer can tell you that if you make electrical contact with an antenna by touching it, it seriously detunes it to the point where any improvement that you might have had from the antenna being external will be lost and then some.
Even if they coated it with a thin non conductive layer, the close proximity of your hand would still have a serious effect on the tuning and performance of the antenna, as even conventional internal antennas in phones which are held at least a few mm away from your hand suffer from significant performance loss from the proximity of your hand, and this whole issue of hand proximity is one of the biggest challenges in antenna design in mobile phones.
So until proven wrong I call BS on Apple's claim of improved reception by using the frame as antennas. If there is an actual improvement in reception then it's more likely to be the glass back (which is far more transparent to 900-2100Mhz radio signals than ABS plastic is) or an improvement in the internal antenna designs, or different radio chipsets, or a combination of the above.
To put things into perspective, I should point out that some loss of signal is normal when picking up a phone - even if you can't make electrical contact by touch (as is the case in most phones where the antenna is inside) due to two effects - shadowing and capacitive loading.
The shadowing effect is that your hand is a "lossy" substance at the high frequencies used by phones, and if you cup your hand around the phone it will block some of the signal through attenuation - just like the wall in your house does. The second effect is capacitive loading, where even though you're not making electrical contact with the antenna, the close proximity of your hand alters the tuning of the antenna ("loads it") which causes the efficiency of the antenna to drop. (The proximity of your head has a similar effect too, so speaker-phone mode will give you a better signal as it's not held close to your head)
These two effects combined depending on the size, shape, and design of the phone, and the way in which it is held cause (with an iPhone 3GS) approximately 10dB of signal loss between the phone lying on a table and being held up against your head.
So if the signal on the table was -95dBm (a typical figure in residential areas from 3, Orange, or T-Mobile) it would reduce to -105dBm, which while not 5 bars, is still strong enough to make a 3G call. (Most phones try to switch to 2G mid call at -107dBm, and will lose 3G entirely at around -113dBm)
The issue we're talking about here is substantial additional reduction of signal - direct electrical contact with an antenna operating at 900-2100Mhz frequencies will severely detune it, (probably resulting in a loss of at least another 10dB, for a total of 20dB) and in the above example would push the signal to -115dBm, which is too weak to establish a connection on 3G. (The phone would have switched to 2G if it could)
So how could Apple miss this effect in testing ? Here's my theory - we all saw the pictures of the lost iPhone prototype - which was in a rubber casing to disguise it as a 3GS. The rubber casing would insulate your fingers from the external antenna, and it is very likely that every iPhone 4 that went off campus during the testing phase was in this rubber disguise case the whole time it was off campus.
The only time they may have used the prototypes without the rubber case were in Apple headquarters in secret darkened rooms - somewhere they're very likely to have strong signals. Apples extreme secrecy prevented them testing it properly in real world conditions.
However this external antenna design should not have got off the drawing board in the first place in my opinion (hence my scepticism of it when first announced) - any radio engineer should be aware of the deleterious effects of making electrical contact with an antenna, so someone wasn't doing their job to let it get this far. My guess is that the industrial designers (Ive & co ?) or Steve himself though it was a great idea and couldn't be dissuaded by the facts and figures of the radio engineers.
So were Apple aware of this design shortcoming by launch time ? I believe so, and here's why. Two unusual things have happened during the lead up to the iPhone launch that on their own made no sense, but if you are a conspiracy theorist, they fit right in.
One is that Apple for the first time announced a rubber case for the iPhone - previously they have relied on 3rd party manufacturers for those, so this is the first time they have made one of their own, and a few commentators were scratching their head over that one.
If I was a conspiracy theorist I would say that Apple realised the mistake in their design too late, and decided to issue the "bumper" cases in an attempt to hide the problem. Funny how the bumper case covers only the metal frame - which should be the strongest part of the phone... I bet Apple store employees have been told to give the hard sell on the bumper cases to "protect" the phone, so that as few people are using the phone without a case as possible.
The other thing is that the field test app has gone missing in OS 4.0 - something I commented on a few days ago as being strange, and I couldn't think of any reason why they would remove it. Well, if you're a conspiracy theorist, I would say that they removed it so that accurate signal strength comparisons between 3GS and iPhone 4 are impossible.
Bars is not an accurate reading, and any signal stronger than -100dBm will show as 5 bars, so it's only if your signal is weak would you notice the bars changing when held as the first video at the top shows. If field test was present a much more accurate numeric comparison with the 3GS would be possible in dBm.
So where does this leave us ? It seems to me that Apple has made a significant design blunder here, (form over function) and their propensity towards secrecy has prevented them properly testing the phone out in the wild, (without a case) and realising the extent of this problem.
Can they do anything about it without a major redesign ? Sort of...they could coat the metal frame with a hard clear-coat like coating which would be thin and invisible, but provide insulation and would dramatically reduce the effects of touching the strip. (It would alter the feel of the surface though...) It wouldn't be as good as a rubber case though, due to the thinness of such a layer.
Is there anything you as an iPhone 4 owner can do about it ? Yep, buy Apple's bumper case and use it. (Or any other case that hides the metal frame) With a rubber case insulating the metal frame from your fingers the signal loss from holding it shouldn't be significantly worse than a 3GS.
I'd be interested to hear from those getting their iPhone 4's how you are finding reception in weak signal areas compared to your 3G/3GS and whether holding it in your hand or to your head makes more difference to the signal strength than the 3GS...(with and without a rubber case)