Apple’s recent problems with the antennas on the iPhone 4 are very well known. Steve Jobs’ talk on the subject and his demonstration of other phone manufacturers’ antenna foibles gave me cause to ponder on the subject a little deeper. Hey, everyone else is taking a shot at Apple about this, why shouldn’t I get in on the action?
Well, Sort Of
I’m not really going to take a shot at Apple. There’s no need since there are plenty of others jumping in, for example Consumer Reports won’t recommend the iPhone 4.
The other mobile phone hardware manufacturers seem to be holding their own in the debate, too. But the real reason I won’t jump on the “Bash Apple” bandwagon is because the truth is, Steve Jobs was correct in his demonstration that other cell phones have similar issues. While I found his demo there in front of a live audience to be a staged PR stunt, his facts were correct.
A Little History
I’ve owned almost a dozen different mobile phones by five different manufacturers. In the users manual of each of those phones a paragraph (or more) was included stating that holding the phone by the antenna (for models with external antennas) or near the antenna location (for models with internal antennas) will degrade performance. This issue has been around since day one of the mobile phone.
It’s All About The Waves, Man
The most daunting aspect of modern mobile phone antenna design is matching the wavelength of the transmitting frequency used by the phones transceiver. Wavelength is the physical length of radio waves in space. It’s an inverse proportion to the frequency (the higher the frequency, the shorter the wavelength). For a short explanation of wavelength calculations for radio waves, check out “Frequency vs. Wavelength” on DXing.com.
Correct matching of antenna length to wavelength is critical for efficient operation of the transceiver, which can have a tremendous impact on battery life. If the match isn’t right, not enough radio frequency (RF) energy will go out the antenna. At best this will cause dropped calls, at worst it will cause damage to the transmitter and make the phone inoperable. Neither of these is ideal.
Back in the day (which wasn’t really all that long ago) cell phones would operate in one or two frequency bands. This made antenna design rather straightforward as it was somewhat of a “one size fits all” situation. Even so, design compromises needed to be made in order to keep the antennas small enough to be convenient. Remember the switch from the pullout metal antennas to the stubby rubber-coated ones? Stashing the antenna inside the phone’s case makes the situation even more complicated.
Because the newer generations of devices do so many things, they need to operate on many different frequencies almost simultaneously. A recent article in the L.A. Times Blog by Mark Milian titled “Building a Better Cellphone Antenna” mentions that new 4G phones will need to operate in up to 40 modes in 50 different frequency bands. This means that the antenna systems in those phones will need to be able to adjust on the fly, switching from one frequency band to another as the phone goes from voice to data to Bluetooth to Wifi modes – and it needs to happen quickly enough that the user doesn’t notice. I’ve read a number of very technical articles over the past few days describing different ways to approach this problem. It’s a technological marvel these newer devices work as well as they do.
A reasoned comparison specifically covering the differences between the first generation iPhone and and the iPhone 4 can be gotten on the AntennaSys, Inc. blog. In this article, the author points out two other very important challenges to mobile phone antenna design: RF energy exposure limits imposed by the FCC and the fact that human tissue conducts and absorbs electricity.
In order to address possible health issues related to long term RF exposure, the FCC places strict limits on how much RF energy can be emitted* from devices based on their frequency (wave length) and proximity to humans. Since mobile phone transceivers operate in the microwave band (typically at frequencies 1 Ghz and up) and microwave length RF energy is easily absorbed by human tissue, placement of the antenna and output power of the transceiver must be carefully balanced in order for a device to get FCC approval. By placing the antenna at the bottom of the phone, more transmitter power can be used in order to allow the device to have better range and (hopefully) reduce dropped calls.
As the author of the AntennaSys, Inc. article points out, the hand is not always taken into account when testing RF exposure limits. The hand conducts electricity just as well as the rest of the body, so when your hand blocks the antenna some of the RF goes into your hand instead of out into the air, thus blocking the signal from the cell tower and increasing the chance of poor performance. Covering the antenna with a bumper case or even duct tape addresses this problem, but doesn’t completely resolve it.
The bottom line is: You have to keep your hand away from the antenna for peak performance. Because people want the antennas to be hidden and marketers like the sleek look of a smooth case, compromises in antenna design are made. As antenna designers continue making improvements, I think you can expect some performance gains. But, since the laws of physics cannot be changed, RF will always be blocked by the human body. There may not be a perfect solution found on the device end. Maybe it would be better to look to the cell tower end of things to help solve this issue.
Why Am I Writing This?
I’ve been playing and working with radios for almost thirty years and I often tell people I’m a radio geek. What started out as a hobby became a big part of my professional life. I first got interested in radio when I bought a boom box which could receive signals on the shortwave broadcast bands. I spent many an hour listening to broadcasts from around the world. Later, my jobs in the Army allowed me to work with many different kinds of radios in different settings. I’m also an amateur radio operator licensed by the FCC (KB5NJU. 73 to all my ham friends).
While I am not an antenna guru, I’m “smarter than the average bear” when it comes to knowing how they work and what what makes one antenna better than another in certain circumstances. I’ve bought, assembled and built from scratch quite a few antennas. While some worked better than others, each one had plusses and minuses. I expect the folks who design mobile phone antennas have similar results in their work, and they’re a whole lot smarter than me on the subject.
Since mobile phones are, at their core, radio transceivers, I hope I explained things in such a way as to help those who are not radio geeks better understand what’s really going on and why mobile phone antennas are very complex and take a lot of delicate balancing to get right.
FootNotes:
* I hesitate to use the words “radiate” or “radiation” because most people think of the type radiation which is emitted from radioactive decay and is much more dangerous than exposure to RF. “Nuking” your food in a microwave is really a misnomer because a microwave oven uses RF energy to cook the food, not atomic radiation.
Top Photo:
photo credit: CalypsoCrystal
{ 0 comments… add one now }
{ 1 trackback }