The iPhone 4 Reception Problems

When the iPhone 4 antenna was announced I commented “This is a very difficult thing to do” in an article on the Wall Street Journal website. (I gave lots of other comments too, though these mostly weren’t used.)

Now the internet is abuzz with discussion of reception problems that have been found with the iPhone 4. Many are blaming the new antenna design. I don’t know for certain what the problem is, but I can make some informed speculation.

Customers who have bought the iPhone have noticed that when they touch a certain place then the reception gets much worse. That place is the small band of plastic in the out metal sidewall on the bottom left.

This video isn’t me, but it’s one of the better videos demonstrating the problem on the net.

A lots of folks on the internet have been asking if this problem is common to other phones. In a press release Apple said:

“Gripping any phone will result in some attenuation of its antenna performance with certain places being worse than others depending on the placement of the antennas. This is a fact of life for every wireless phone. If you ever experience this on your Phone 4, avoid gripping it in the lower left corner in a way that covers both sides of the black strip in the metal band, or simply use one of many available cases.”

It’s quite true that other phones suffer from similar problems. There are now several videos on the internet showing the signal strength report on various phones deteriorating when they are held. This has been shown using old Nokia phones, Blackberries and earlier iPhones. This is a well known problem. The important question though is: does the iPhone 4 suffer from it *more* than other handsets? In my opinion from the evidence available online the answer to that question is “Yes”.

The human hand contains a lot of water and other materials which absorb EM waves. It is also strongly dielectric, muscle has a dielectric constant of ~56. So, any capacitive effects are strengthened by the presence of the hand. Both of these have an effect on antenna performance. Suppose you cover over the antenna on your handset with your hand. Because of the absorbtion less radiation reaches the basestation. Also, the antenna contains distributed capacitance, this capacitance is increased by the dielectric properties of the hand, the antenna become more dielectrically loaded. The antenna has been tuned to work at the design frequencies with the normal capacitances. This disturbance causes “detuning” and the performance of the antenna reduces at frequencies bands it was designed for. Often there is a frequency shift and the antenna’s bands of good performance move up in frequency or down. People talk a lot about the absorption effect, but in practical cases the dielectric effect is often more important.

The magnitude of this problem was measured by G.F.Pedersen in several papers that comprise his PhD thesis. Pedersen got many people to hold a mobile phone like they would in a phone call and measured it’s performance as they held it, to find out the loss caused by the proximity of the head and hand. He collected the data for several types of antenna, including an internal PIFA antenna mounted at the top of the handset. Pedersen’s measurements show a great range of performance depending on how the specific characteristics of the user, such as how they hold the phone, the size of their head, etc. He found that for the PIFA antenna the average degradation was ~3dB. In the past I’ve found that modern handsets with internal PIFA antennas close to the top are a little worse than the one Pedersen used, but not much worse, I’d estimate the loss at 3 – 6dB. Those with PIFA antennas at the bottom are worse because because the user tends to cover over the antenna with their hand. I don’t have an estimate for the loss in that case.

The iPhone 4 doesn’t report the signal strength in dBs. Like most phones, it indicates it to the user by showing “strength bars”. At present nobody outside Apple knows how those strength bars work. The may include data other than strength too, such as signal to noise ratio. However, the various videos in the internet do show the signal strength dropping from 5-bars down to no-signal. Normally when a phone gives “full-bars” that means it’s receiving at least 10dB more than the minimum it can cope with. Often full-bars means that the phone is receiving 20dB more than the minimum. This indicates that the performance degradation for the iPhone 4 is especially bad. I can’t be sure of that, but that’s my view from the available evidence.

There are several ways that this problem could occur. Firstly, the loss introduced by placing a hand around the phone may be especially high. I don’t think this is likely because there have been demonstrations on the internet that show the problem is associated with a particular area on the phone. If the plastic band at the bottom left is touched then the performance deteriorates. The most likely explanation for this is associated with dielectric properties. If there is a lot of fringing capacitance between the two pieces of metal at either side of the gap then placing a dielectric object – such as a finger – across the slot will radically change the capacitance. That it turn will change detune the antenna and reduce the performance in some bands.

Some folks have suggested that the problem could be due to conductivity. They’ve suggested that the moisture on people’s fingers may cause a current path between the two pieces of metal. This is possible, if it did happen it would certainly cause big problems. Some folks on the internet have put a coin across the gap and showed that this causes performance degradation. However, there are some videos now showing the problem occurring with iPhones in rubber and plastic cases. These cases are unlikely to conduct well at GHz frequencies, so I think the dielectric explanation is more likely.

Some people aren’t reporting any problems with their iPhone. That’s not really so surprising since lots of people live in areas of high signal-strength (see my post on networks). Also, if dielectric detuning is the problem then it will not affect all bands and channels equally. It may be that some bands are entirely unaffected. So, we should expect only a subset of users to be affected.

Starting with the iPhone 4 Apple have started offering a cover, called a “bumper”, for the iPhone. It’s interesting that the experiments with covers and outer cases have been inconsistent. Sometimes the cover has solved the problem, sometimes it hasn’t, sometimes it’s helped a bit. This could be because the various covers are different, some dielectrically load the critical parts of the antenna, and some don’t. Perhaps some allows the users hand close enough that it causes dielectric loading but others keep the hand further away.

Lastly, an answer to something that has puzzled a few people – why does the signal strength display change so slowly? That’s because these sort of displays use averaging. They average the signal strength measurements over the last few seconds. So, even if the signal strength changes quickly the display doesn’t. This is a feature to make the display more user friends, all handsets do it.

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25 Responses to “The iPhone 4 Reception Problems”

  1. Gravatar of bpresles bpresles
    29. June 2010 at 19:36

    Very nice articles on the iPhone 4 antenna and it’s reception problem.

    I’ve a question about the reception problem and as you seems to know a lot on the antenna and radio waves field, you may give me your opinion on it.

    Considering that the issue is, according to you, related to dielecteicity, do you think Apple can do something on the software level (I.e the BaseBand dirmware) to reduce or solve the problem, or will they have no other choice than to modify the hardware itself?

  2. Gravatar of rt rt
    30. June 2010 at 02:16

    It may be that the problem has a software component. For example, the signal strength bar display could be exaggerating the problem.

    Since I wrote the post I realised something else. The gap in question is reportedly between the antenna for Bluetooth+WLAN+GPS and the cellular antenna. It could be that the extra capacitance across the gap caused by the hand causes RF signals from the other antenna to leak across. If that is the case then they could try turning off Bluetooth and WLAN whenever the cellular antennas is being used. (I’ve noticed some folks on the internet have tried turning off WLAN, but I haven’t seen a test with both Bluetooth and WLAN off).

    Those two options are quite long shots though. I can’t think of any other possibilities except modifying the hardware.

  3. Gravatar of bpresles bpresles
    30. June 2010 at 05:35

    I’ve personnally tried turning both bluetooth and WiFi off, in fact I mostly usethephonethisway becauseI turn Bluetooth andWiFi on only when I really need them,for battery life purpose.

    And that doesn’t change anything for me, I’ve the exact same amount of signal lost, same number of bars reduction. So apparently that has nothing to do withhaving Bluetooth and WiFi turned on or off.

  4. Gravatar of rt rt
    30. June 2010 at 12:37

    > I’ve personnally tried turning both bluetooth and WiFi off,
    > in fact I mostly usethephonethisway becauseI turn Bluetooth
    > andWiFi on only when I really need them,for battery life
    > purpose.

    That’s interesting. Well, that rules out one possible explanation.

    Since you have one of these phones could you possibly do a simple experiment with it?

    It would be very interesting to know if the surface conductivity of the hand really makes any difference. This could be tested by comparing with a water-filled body with a surface conductivity that’s known to be low.

    The outside of a plastic bottle has low surface conductivity if it’s dry. But, if filled it with water it will have a similar dielectric constant to human tissue.

    Do you have a plastic bottle with flat sides? If so, could you fill it up with water. Then put the iPhone on it’s edge on a flat side of the bottle. So the gap is in contact with the side of the bottle, which has water directly beneath it.

  5. Gravatar of GeekPub GeekPub
    30. June 2010 at 21:28

    I’ve done a lot of testing and wrote a review on the iPhone 4. You can read it here if interested:

    From what I can tell in my testing, if you’re hand is sweety (i.e. saltwater) BIG problems. If I dry my hand very dry under and an air dryer, I can almost completely eliminate the issue.

    I have to believe Apple knew about this before they shipped it.

  6. Gravatar of rt rt
    30. June 2010 at 22:24


    > From what I can tell in my testing, if you’re hand is
    > sweety (i.e. saltwater) BIG problems. If I dry my hand
    > very dry under and an air dryer, I can almost completely
    > eliminate the issue.

    That makes me wonder if I’m wrong, maybe skin conduction is an issue.

    But, skin conduction doesn’t work very well at GHz frequencies. Pure water doesn’t conduct electricity. But, once minerals like salt are dissolved in it then it will conduct. This is because the ionic bond in the mineral breaks produces two ions, Na+ and Cl- in the case of salt. This process gives good conductivity at low frequencies. But, as frequency increase the conductivity gets worse quite rapidly. That’s why I was a bit sceptical that skin moisture could produce a significant amount of current flow.

    But, I suppose I could be wrong, since the gap is only small skin conduction may be the problem. That doesn’t seem to explain why some folks have found that their rubber and plastic cases don’t prevent the problem. Perhaps they’ve got them wet, or some types of rubber case are conductive.

    It could be that both conduction and change in capacitance play a role.

  7. Gravatar of Dave Dave
    1. July 2010 at 01:21

    Another suggestion, bearing in mind that Apple products tend to be made of cheese: try pressing the area in question with something totally non-conductive – a bit of wood, say. There’s always a chance that there’s actual physical contact of conductors going on when the case is squeezed.

  8. Gravatar of David Kanter David Kanter
    1. July 2010 at 19:08

    I’ve seen (and participated in) demonstrations at ISSCC, where researchers from KAIST showed that you can transmit enough raw data for playing music across the skin (from an audio output to a speaker, instead of using speaker wires).

    Based on that, there should be a fair amount of conductance.

  9. Gravatar of rt rt
    1. July 2010 at 19:59

    What was the frequency they were using though? Was it as high as 800MHz?

  10. Gravatar of Brian Mccants Brian Mccants
    2. July 2010 at 19:43

    This phone is FAST. The screen is beautiful. Multitasking! (finally) Camera is awesome (and also faster), camera flash is surprisingly bright. Even the speaker is louder and clearer. Battery life is noticeably longer. Lots of little improvements.

  11. Gravatar of rankpay promo code rankpay promo code
    5. July 2010 at 21:47

    From the reviews I’ve seen, the iPhone 4 still has better reception than the 3GS even with the attenuation. So yes, you’ll see degradation, but still better upload and download than a 3GS. Especially since the 4 supports HSUPA and the 3GS doesn’t. It’s a questionable design to be sure; why couldn’t they just build in some kind of bridge to prevent the attenuation in the first place? But for the most part it seems the 4 is catching flack for an improvement in quality. I don’t have a 4, so I can’t test this myself, but I’d be interested to see the 3GS side by side in any showing of 4 degradation issues

  12. Gravatar of rt rt
    5. July 2010 at 22:21

    > From the reviews I’ve seen, the iPhone 4 still has better
    > reception than the 3GS even with the attenuation.

    That’s not what the Anandtech data suggests. It’s quite possible that performance depends on band and channel though.

    The addition of HSUPA is certainly welcome. But, that mostly helps throughput in places where the signal strength is strong.

  13. Gravatar of online jobs online jobs
    6. July 2010 at 12:01

    I love your website! did you create this yourself or did you outsource it? Im looking for a blog design thats similar so thats the only reason I’m asking. Either way keep up the nice work I was impressed with your content really..

  14. Gravatar of rt rt
    6. July 2010 at 12:11

    Yes, I wrote the website myself. The wordpress style I’ve used is “simplicity bright”.

  15. Gravatar of The Case of Apple and the Mysterious Bars – The Numbers Guy – WSJ The Case of Apple and the Mysterious Bars - The Numbers Guy - WSJ
    9. July 2010 at 23:53

    [...] reported by signal strength displays,” said Robert Thorpe, an antenna consultant who also has blogged about the iPhone signal bars. “So, the display doesn’t represent the whole [...]

  16. Gravatar of Mae Dardy Mae Dardy
    11. July 2010 at 12:38

    And to think all that’s needed is some tape to fix it!

  17. Gravatar of Digitalia #59 – La testa piena di numeri | Digitalia Digitalia #59 – La testa piena di numeri | Digitalia
    14. July 2010 at 08:17

    [...] Perchè un isolante potrebbe non essere abbastanza per risolvere il problema antenna di iPhone4 [...]

  18. Gravatar of Neely Stthomas Neely Stthomas
    16. July 2010 at 08:16

    Regardless of the pessimistic announcement of the iphone 4 we reallyabsolutely adore this amazing nice device.

  19. Gravatar of
    17. July 2010 at 06:47

    We’re sure Steve can solve the new iPhone as soon as possible.

  20. Gravatar of Children Allergy Guru Children Allergy Guru
    17. July 2010 at 17:05

    I managed to get one of the very first iphones and have been soooo happy with it. Since iphone4 was out I am thinking of upgrading, however, not with this blunder which Apple produced! I was surprised that they could be so stupid!

  21. Gravatar of Javier Kaeding Javier Kaeding
    18. July 2010 at 14:20

    I have enjoyed my Iphone since the first one was released. It truly is an amazing device and it reminds me of what people in the 50s thought the future would be like.

  22. Gravatar of Quinn Szalay Quinn Szalay
    20. July 2010 at 01:13

    “Steve Jobs, expresses annoyance with the critical coverage of the phone’s reception problems” Maybe if the Apple company fessed up sooner the media storm wouldn’t have gotten so ovewhelming. I think Apple thought if they avoided the problem it would disappear. Obviously Apple is absolutely on its way to become the company they once avoided being like.

  23. Gravatar of Elisha Pelyo Elisha Pelyo
    23. July 2010 at 09:21

    It’s funny that Steve Jobs offer a free case for buyers. A new case can solver iPhone 4 antena problem?

  24. Gravatar of t-shirt bio t-shirt bio
    30. July 2010 at 12:22

    Apple offers customers a free case until September 30 or a refund within 30 days of purchase because of the signal problems. Nevertheless, the new screen is so bright and so clean.

  25. Gravatar of Donovan Lewan Donovan Lewan
    2. August 2010 at 15:22

    People complain too much about the iphone 4 problem but I don’t see any problem with it