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How does the iPhone 4 antenna system actually work, and what's wrong with it?

J

JoshHawn

macrumors member
Original poster
Mar 21, 2008
88
0
Hanford/Lemoore, CA
Apple has designed the iPhone 4 so that the stainless steel band around the phone is "part of the antenna system" and "Is the result of some really cool engineering."

Well, if it is just part of the antenna system, what's the rest of the antenna system? How can two strips of metal wrapped around the phone (something that doesn't seem all that technical) be an important part of the antenna system?

The answer: it isn't!

After doing some investigating of my own, I learned of another part of the antenna system located on the backplate of the phone, under the glass.

I found out by asking what this is:

Pressure_Contact.jpeg

Photo courtesy of iFixIt.com

The answer was that it was part of the antenna system. This pressure contact touches a small area on the backplate of the phone which is part of a separate antenna array.

Backplate_Antenna.jpeg

Photo courtesy of iFixIt.com

My theory:

This backplate antenna is the actual functional antenna inside the iPhone 4. Stainless steel isn't a good material to make an antenna out of anyway because it has around 10 times more resistivity than copper. This backplate antenna has to be an actual highly-engineered multi-band antenna for the iPhone 4 that serves as its GSM/EDGE and UMTS/HSDPA/HSUPA antenna which makes a lot more sense than having this stainless steel band do all the work.

So what's the problem with the signal loss if the antenna is on the back? Well, the stainless steel frame is still connected to the antenna system probably just to pick up extra RF modulations that can be filtered into the circuitry to help boost the signal a little bit, but when you touch the bottom left seam, shorting out the antenna, all the RF signal is grounded out through the separate WiFi/Bluetooth/GPS antenna :eek:

My hypothesis is that disconnecting the stainless steel frame from the antenna system would completely solve this signal loss issue.

I rest my case! :cool:
 
RyanG said:
[size=+5]stainless steal[/size]
Click to expand...

Mac Rumors Rules
12. Corrections. There is no need to point out another poster's spelling or grammatical errors unless you think it is causing confusion. Remember that not all members are native English speakers. Communication, not correctness, is our goal. Examples: Don't correct members who spell Mac in all caps or who call the iPod touch an iTouch.
Click to expand...

;)
 
JoshHawn said:
This backplate antenna is the actual functional antenna inside the iPhone 4. Stainless steal isn't a good material to make an antenna out of anyway because it has around 10 times more resistivity than copper. This backplate antenna has to be an actual highly-engineered multi-band antenna for the iPhone 4 that serves as its GSM/EDGE and UMTS/HSDPA/HSUPA antenna which makes a lot more sense than having this stainless steel band do all the work.
Click to expand...

You said it in your original post. I wouldn't want you to explain this riveting and groundbreaking discovery only to create confusion with misspelling such a common word.
 
RyanG said:
You said it in your original post. I wouldn't want you to explain this riveting and groundbreaking discovery only to create confusion with misspelling such a common word.
Click to expand...

haha! yeah, I spelled it wrong once... Once! I fixed a couple of other typos I found, too. Thanks though! Glad someone's looking out ;)
 
JoshHawn said:
haha! yeah, I spelled it wrong once... Once! I fixed a couple of other typos I found, too. Thanks though! Glad someone's looking out ;)
Click to expand...

I'm glad you realized I was only messing around. Nice to see some people with a sense of humor around here.
 
Apple-NoEscape said:
Do you actually been a life part? Or a live part? I'm not trying to be a spelling Nazi I'm just generally confused.
Click to expand...

I understand. Electromagnetic Radiation is a very confusing subject. I think he means that there is usually two contacts on an antenna system instead of just one.

I think that one contact is all it needs to measure the voltage/current oscillations from the antenna. There are usually two contacts for a dipole antenna, but I'm sure cell phones these days use fancy fractal-geometry antennas.

now that just sounds more confusing :rolleyes:
 
JoshHawn said:
I understand. Electromagnetic Radiation is a very confusing subject. I think he means that there is usually two contacts on an antenna system instead of just one.

I think that one contact is all it needs to measure the voltage/current oscillations from the antenna. There are usually two contacts for a dipole antenna, but I'm sure cell phones these days use fancy fractal-geometry antennas.

now that just sounds more confusing :rolleyes:
Click to expand...

See in electronics I have always had a 'live' wire etc and a ground(ing) wire. Names ovbiously explain what they do. I was just confused as too whether he actually meant life or not.
Never heard of a 'life part'. Ah well you learn something new everday :D
 
It really all boils down to the antenna being resonant to the device to work properly.
This applies to both transmitting and receiving.

In regards to transmitting (the harder part), there is a specific frequency that the unit transmits on. This frequency is looked at in terms of wavelength. A higher frequency will have a shorter wavelength therefor a shorter antenna is needed. Cell phones transmit at a pretty high frequency so we can have a short antenna.

An example would be a transceiver (transmitter/receiver), like your phone, transmitting on the 2 meter wavelength frequency such as 146.970 MHz. Ideally for the transmitter to work at it's best, the antenna length would match (be the same) length of the frequency wavelength the unit is transmitting on. This is an antenna being resonant, the ideal situation. If it isn't it would add additional resistance (or not enough) to the transmitter other than what it was designed for.
This is similar to a stereo system that was designed to use 8 ohm speakers and you hook up 32 ohm speakers. It would not sound as good and eventually hurt the system.

The hard part is how to put an antenna that is 2 meters long (our example) on a small device. You cannot have a handheld unit (like a cell phone) with a 2 meter long wire (antenna) hanging off it.

To accommodate this problem we found that you can use divisions of the full length (ideal), such as 3/4, 1/2, 1/4, etc. of the full length and still be resonant (not as ideal but will do). This helps the problem of needing an antenna that is way too long to use in your home or car.

I should add that the same thinking holds true to good receiving.

Now to the iPhone (or any cell phone). The are multiple antennas because the unit uses several frequencies as you know. It takes a LOT of RF engineering to figure out how to pack each antenna into a small unit and have them all be pretty much resonant. Yes, if you short one that is being used at the time to a ground or another antenna it will no longer be resonant and your signal (transmit or receive) will not be as effective. This might be the problem that the iPhone is experiencing. Therefor a case or bumper would do the trick.

What the antenna is made of, assuming they are all metal, does not matter. Stainless might have a higher resistance in general than cooper but that is accommodated for in the transmitters design to keep the impedance (resistance) of the antenna the same as the transmitters impedance (think resonance). So any metal will do.

Hope this helps in any way.
 
Antenna theory is pretty simple but when you start trying to cram multiple antennas into a confined space it can get pretty complex pretty fast. Cellphones are a good example. Most of the time they use a dipole or a folded dipole and at the frequencies cellphones use, a halfwave dipole isn't very big. The problem with a dipole is that it's directional and it won't make people happy if they have to aim the phone a certain way in order to use the phone. To get rid of the peaks and valleys of the radiation pattern you detune the antenna by making it slightly longer or shorter than it should be for it's frequency of operation. But now you've changed the resistance of the antenna and it won't match the resistance of the transmitter. That causes power to be radiated back to the transmitter where it's lost as heat. If it's bad enough, you'll burn out the transmitter. Therefore you either change the resistance of the the transmitter or, more likely, you change the resistance of the antenna by placing a coil on both sides of the dipole. You can see this in a lot of phones as a "maze" looking trace on the board containing the antenna traces. Now the antenna is relatively omnidirectional and allows maximum power transfer from the transmitter but that doesn't mean the antenna is actually any good because it's still not the proper size for the given frequency, it's inside a box that's crammed with metal electronics and being held in your hand.

Given how lousy iPhone reception was with the 3G and 3GS, my guess is Apple used the metal band around the phone as part of the antenna because it gets it outside of the phone, a little further away from the electronics and lets it grab a little more of the signal. Any antenna is better than no antenna and, as mentioned, the metal doesn't really matter as long as the resistance is matched. Also, while the capacitive effect of your hand can detune an antenna, the larger the actual conductor, the less of an effect your hand will have. To make it the length they needed, they cut the band and put non-conducting material in the seams. If you put a conductor across those seams, you lengthen the antenna drastically which causes the signal to drop and that's exactly what happens with my phone. Since reception is fairly poor at my house to start with, the moment I short across a seam with a wire, any call is dropped. Your hand is a poor conductor but still a conductor or it wouldn't be possible to be electrocuted and therefore holding the phone in a manner that shorts over a seam will have the same effect. That also means that this entire mess could have been entirely avoided by coating the metal band with a non-conducting material.

All that having been said, the upside is that reception is measureably better with the iPhone 4 than previous iPhones. About 20 minutes after I bought the new phone I bought a nice case at AT&T which eliminated the antenna problem and now I have 3 to 5 bars at home where before I had 1 to 3 at most. I've held conversations on the new phone over 20 minutes in length that ended when I ended them where before I was never able to hold a conversation longer than 5 minutes before the call was dropped. Ever. So the new phone is actually considerably better than previous phones.

So why all the hate when it's actually better? I see three reasons. First, it was a surprise. Everyone is expecting it to walk on water and then change that water into wine and instead find there's a bizarre, serious reception problem. Second, no one really understood what was going on. Was it the new OS? Was it the hardware? Was it the metal? The seam? The sim card? Apple wasn't saying a word so all anyone could do was guess. Third and most importantly, Apple's (Steve Job's) immediate response to the problem was infuriating and asinine. Sure it's "only a phone" but it's a damned expensive phone and it had better work like a damned expensive phone. It also didn't help at all that when the problem started cropping up everywhere, the usual people posted their usual crap about how Steve Jobs is the second coming of Christ so this had to be a user error and all the rest of that garbage that, as usual, was gas thrown on the rising flames. Apple would have done a lot better to stick a muzzle on Jobs and release something acknowledging the problem, that they were looking into it and a resolution for current iPhone owners and that they would be notified if and when a fix was found. People would still be upset but they wouldn't be seething and it wouldn't be fodder for the competition's advertising. For a company so obsessed with it's image, it's kind of funny how clueless they can be when dealing with their own customers.
 
You make a good point about power factor matching with the added resistance, but I don't really think it would matter all that much because actual power factor correction involves complex impedances and there aren't any capacitors or inductors in this stainless steel band that I can see.

Another problem I see with it is: Why does the problem only occur at the bottom left seam and not on the top seam? I did some more investigating to try to figure it out, and even thought of a way to fix the problem:

Steel_Contact.png

Photo courtesy of iFixIt.com

See that brass screw mounting point on the right? That's what brings the larger stainless steel band into contact with the antenna system. Interestingly enough, it's located right where the signal attenuation problems occur! (This is the back of the iPhone, so it's located on the lower right rather than lower left). When you bridge that seam whether it be with your finger or any conductive material, it shorts out the antenna! This is a small enough distance that it has an effect. This would explain why the signal attenuation does not occur at the seam at the top of the iPhone 4, near the headphone jack: because it's too far from this location for the current to be grounded to the Wi-Fi/Bluetooth/GPS antenna. That extra length makes the resistance too high for there to be a significant short across to the other part of the stainless steel band.
 
That could be. It could also be that the two sections address two different frequencies so only one has an effect at a time. Also, impedance matching can occur anywhere outside of the transmitter. The difference is this: If a ham radio operator wants to use a single band that uses an antenna larger than his yard, he'll put coils in that single, shorter than required antenna to match the impedance. Case closed. If he wants to use multiple bands using a single antenna (fewer antennas than bands), however, that won't work. Instead, he'll usually use an impedance matcher at the transmitter which contains variable capacitors and coils and allows the operator to tune the transmitter to almost anything. Obviously the phone won't have variable components but it's using a fixed number of bands with a fixed number of antennas. Those components may not be obvious and they may be anywhere between the antenna and the transmitter and/or part of the internal antenna itself. A "coil" can be a couple notches in a board trace, a capacitor can be two traces a certain distance apart. As long as it's electrically correct, it can be almost any kind of bizarre physical component.

I was going to add that before anyone goes feeling sorry for the RF enginneers, antenna design isn't rocket science. It's really not that hard to design one for almost any circumstance using a computer. Nokia, Motorola and SonyEricsson are known for phones that work perfectly in places where other phones don't work at all. The "real" question, in my opinion, is how did Apple miss something that took me and lots of others minutes to notice? What kind of culture exists at Apple that would totally miss a problem this glaring? I like my Apple products, and I have several, but I paid a premium for those products and the assumption was always that you pay a premium for Apple because the quality of that product is higher than that of the competition or, when you did have a problem, support was top notch. This problem with this iPhone has certainly blown all that out of the water, hasn't it? We know it has a problem with it's antenna and the camera has a problem under certain lighting, what else is wrong with it? What other arrogant dismissals can we expect from the CEO of the company that produced it? Personally, between this and the video problems I experienced with my Macbook Pro, I don't have a whole lot of confidence in Apple any longer.
 
Well, I finally tried out my theory by taking my iPhone 4 apart to insulate that brass screw bracket from the metal band.

Results: No change :(

I put it back to how it was before. I guess all I can do now is "stay tuned."
 
RF window

Someone told me the backplate is actually a RF window for both the cellular and wi-fi antennas.

I don't know much about antennas and RF windows. What is the main function of the RF window in the iPhone 4? Is it catching more RF for the antennas? What is it doing?

Sorry to drag up such an old thread but it's driving me nuts! I just am very curious about the antenna system of the iPhone 4!

Thanks!
 
imagineadam said:
Someone told me the backplate is actually a RF window for both the cellular and wi-fi antennas.

I don't know much about antennas and RF windows. What is the main function of the RF window in the iPhone 4? Is it catching more RF for the antennas? What is it doing?

Sorry to drag up such an old thread but it's driving me nuts! I just am very curious about the antenna system of the iPhone 4!

Thanks!
Click to expand...
It's my understanding that that's why when went with a glass back instead of something more reasonable.
 
Sedrick said:
It's my understanding that that's why when went with a glass back instead of something more reasonable.
Click to expand...

What? This doesn't explain or help me with what I asked or make much sense. Please fix your grammar or elaborate some more please!
 
Last edited:
I'd just like to say that this is the first thread on the topic that has made any sense whatsoever....

For those of you who have posted here who seem to know something about antennas, is it true that cupping a phone will always attenuate the signal? If not, then maybe the iP4 detractors have a point, and for all of you who I accused of whining, well, :eek:.
 
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