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Andrew Seybold: iPhone 4 Antenna Shortcomings Signal Different Challenge

Device placement is more complicated, complex than it might appear

When it was reported that the new iPhone 4 used the metal band around the outside of the phone for the antenna and that if you held the iPhone wrong, the signal disappeared or got weaker, there was a flurry of articles about this method of antenna placement. Soon after, Apple announced that part of the problem was its software formula for determining signal strength and showing how many “bars” of signal were available was in error and that in reality the signal strength was lower than that being indicated.

Andrew Seybold
Andrew Seybold

What I have not seen are discussions of the overall issue of antennas and their placement on wireless devices. A number of interwoven issues contributed to the problems encountered on the iPhone 4. First, the antenna, its effectiveness and its location, is the weak link in any wireless or radio system. If you watch TV with an outside antenna and disconnect the antenna from the TV set, there is no reception. If the antenna on your car breaks, you don’t have any AM or FM reception. This is because these systems are designed with the understanding that there will be an external antenna.

In analog cellular days, every phone had an external antenna, which gave the device better range when communicating with cell sites. When we switched to digital but analog was still operational, antennas were still external. Today, our wireless network operators have built out many more cell sites — AT&T and Verizon each have more than 40,000 sites to cover the United States. Still, we don’t have good coverage inside buildings or in areas where the nearest cell site is at a distance. But since coverage is many times better than it was earlier, the handset vendors and network operators decided to hide the antennas inside the devices to make them more appealing and easier to carry. However, this has had the undesirable effect of making them less sensitive than earlier devices that had external antennas.

A number of interwoven issues contributed to the problems encountered on the iPhone 4. First, the antenna, its effectiveness and its location, is the weak link in any wireless or radio system.

Better coverage is the primary reason you will find external antennas mounted on police, fire, and other vehicles that make use of two-way radio. You will also find external antennas on family radio walkie-talkies and handheld two-way radios used by first responders and others. Nextel employed external antennas on its phones (and some still have them) to enable customers to receive and send wireless information when in lower signal areas.

We are not talking here about a single antenna for the iPhone or for any other wireless device. Antennas have to be matched to the frequency on which they operate. The match has to be such that as much power as possible is transferred to the antenna from the transmitter. A mismatched antenna can result in poor radio coverage, heat buildup inside the radio and, therefore, shorter life for the device. Antenna experts are very good at designing antennas to be as efficient as possible, but in the confines of a handheld device, there are trade-offs that must be made.

Radio waves are absorbed by our bodies, by walls, and even by vegetation. Some of you might have experienced different performance from your wireless devices in the same location in the winter than in the summer. This is because leaves and even pine needles can soak up a radio signal and cause the overall system to degrade during the spring and summer. Also, since radio waves sometimes arrive at your device not directly from the radio tower but rather by being bounced off a building or hill, these signals may be much lower in strength than if you had a clear line-of-sight view to the cell site.

All of these factors affect the performance of our wireless devices, but we need to add yet another parameter to all of this: Today’s wireless devices need multiple antennas in them. A typical “world phone” operates in four to five different portions of the spectrum from 800 MHz through 2.1 GHz or higher. Then there is the antenna needed for Bluetooth, another for WiFi if it is built in, and one for the GPS receiver. If you have mobile TV capabilities built in, there will be another antenna to receive, say, MediaFLO TV signals on 700 MHz. Soon, Verizon first then AT&T and others will be adding the 700 MHz band to these devices and the number of antennas needed inside a wireless device will increase again. Most LTE systems will make use of two antennas in each wireless device to increase both the coverage and the data speeds.

As I mentioned, antenna design engineers have become very good at what they do, but since each antenna must be electrically matched to the transmitter and receivers, it has to have certain characteristics that differ from the antenna for another portion of the spectrum. Today, these engineers have been able to design fewer antennas into these devices by making one antenna do the work of several, but there are limitations to what can be done. All of this also means that any company designing and building devices that does not have access to engineers who really understand the antenna systems that are required will have a problem building a device that works as well as someone else’s device with a better antenna system.

Some of you might remember when WiFi was first being built into notebook computers. My company, as well as many others, ran tests to determine range and speed and found significant differences (the weaker the radio signal, the less data speed). Today, all of these notebooks offer about the same level of coverage, but in those days there were huge differences. What we found was that the computer companies that hired or brought in antenna experts had products that performed better than those that thought they could simply build an antenna and put it inside a notebook. Not only is the length of the antenna important, where it is placed inside the device is just as critical. Since it is radiating radio signals, it could interfere with the device’s receiver, or some of the radio waves could be absorbed by other components and even more can be absorbed by the placement of a hand over the portion of the phone where the antennas are located.

As you can see, the entire issue of antenna design and placement is critical to the performance of a wireless device. What Apple was trying to accomplish was twofold. First, Apple was trying to gain room inside the iPhone 4 to make it thinner and to hold a larger battery. Second, it was trying to move the antenna(s) outside of the device, as if using an external antenna sticking out the top. I have not tested an iPhone 4 in our lab, but will be doing so once Apple resolves the software signal strength issue. It is easy to understand why it was caught off guard by the complaints about poor coverage, however.

There is one more variable that needs to be taken into account. When your car radio receives an AM or FM broadband signal that is all that is happening — it is receiving the signal. Depending on the technology your network operator is deploying, however, it is possible that your phone is both transmitting and receiving at the same time. This creates additional problems in design because the same antenna that is “listening” for a signal is also transmitting a signal on a different portion of the spectrum at the same time. Unless these systems are designed carefully, the transmitted signal can cause noise in the receiver and it will not be nearly as sensitive.

Perhaps the matter of receiver sensitivity deserves a mention about now. Receivers are designed to hear signals that are received by their associated antenna and then process these signals. However, if there is a lot of noise (interference) on the channel the receiver is listening to, it cannot detect the signal intended for it because it is covered by noise. Also, different types of receivers have different degrees of sensitivity. To better understand this, visualize a single grain of sand. Hold that grain of sand between two of your fingers and you will hardly feel it. However, if you put it into your eye, it will feel like a boulder! In this case, your eye is a more sensitive “receiver” than your fingertips. The more sensitive a receiver, the better coverage the customer will experience.

Normally, when testing these devices the first tests are performed in a controlled environment where other radio signals are blocked (in a screen room) and the device is mounted in a test fixture, not held in someone’s hand. The final tests, just as the product is ready for market, are the field tests. It is very possible that the differences in coverage were not noticed because the same person was testing the iPhone 4 as a standalone device and not against other devices in the same area. Once again, it is important to understand that antenna design needs to be carefully developed, and even then it is part science and part art. The antenna experts who work on these devices clearly understand the art part.

The transfer of radio signals to and from the antenna and the radio receiver and transmitters, and the efficiency with which that is accomplished, determines how well the device will perform. For voice, the difference will be a clean completed call or a noisy dropped call. For data services, the better the signal strength, the higher the data rate in both directions. If your device is not designed properly, your results will not be as good as those of someone standing next to you with another, better-designed device.

I am not saying the iPhone 4 was not designed properly; I have not had one in my hands nor seen the antenna configuration. But it does appear to me that Apple’s goal was to provide for better performance and a better data experience for its customers. If the “fix” is to put a rubberized case around the device to keep hands from touching the metal portion of the phone, that is simple enough. If this type of fix does not prove to be workable and there is something more involved, I am sure Apple and the network operators will figure it out and come up with a more satisfactory solution.

The point of this commentary is not to beat up Apple for what might have been a design mistake. The point is that the entire issue of antenna design and placement is extremely complex, and the antenna is the weakest link between our wireless device and the cell sites. Further, I am not talking about a single antenna here, but rather multiple antennas each needing to be the best they can be, stuffed inside the device in the smallest possible space without interfering with each other or the radio and computer components inside the same box.

It is truly amazing to me that we have engineers who possess the knowledge and skills necessary to make all of these variables work together, and I suspect that moving forward we will find more examples where new antenna placements might be tried — some will work and some will fail. Regardless of how good a computer model you build to prove out the performance of these antennas, until you put them on or in the device and turn it on, you cannot be 100 percent sure of what the results will be — that is the art that goes along with the science.

— Santa Barbara resident Andrew Seybold heads Andrew Seybold Inc., which provides consulting, educational and publishing services. Click here for more information.

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