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The Incredible Shrinking Antenna
pinkUZI writes "NYTimes ran an article yesterday about a new material, created by a general manager at Integral Technologies, that would enable use of the plastic mold of a cell phone as its Antenna. Pretty neat, as it actually increases the size of the antenna while decreasing the footprint."
With antenna-less phones, like the Nokia 8260 and the Nokia 3360, I don't worry about antennas anyway, and these phones are here now, and work with my wireless company!
Disclaimer: I'm not an employee of either, but I do use rogers...
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Some weasel took the cork out of my lunch.
800 MHz cellular has a wavelength of approximately 37 centimeters, about 15 inches. So an ideal antenna would be half that, about seven and a half inches. This refers to the dipole, the distance from the tip of the antenna to the opposite end of the antenna buried inside the phone somewhere (usually near the bottom). 1900 MHz PCS has a wavelength of approximately 16 centimeters, about six inches. So the ideal antenna dipole is about 3 inches.
The ideal antenna performs best if it is exactly perpendicular to the impinging waveform. In practice the orientation of the phone is somewhat random; the antenna will be pointed approximately upward, but probably at a slant. So cell phone manufacturers generally try to make the antenna 5/8's of a waveform, because if the antenna is at a slant, its cross-section relative to the impinging waveform will be near to the ideal half a wavelength. For a dual-band phone, one which operates at both 1900 and at 800 MHz, it's obvious that determining the antenna length is a bit of a problem. (But not insoluble; it's just a compromise. Since digital is usually more resilient than AMPS, usually the length is optimized for 800 MHz.)
Making the antenna shorter will both decrease the amount of incoming signal the phone receives, and will make the phone's transmitter less efficient. But CDMA operates over a very wide range of effective powers, and it can usually compensate. That's why the phone will usually work with the antenna down. And because it's digital, if it is working it will sound exactly the same. This has lead some people to conclude that the antenna is not actually doing anything for them, which is not quite correct. While the phone can operate with the antenna down, it's easier on the phone if you raise the antenna; it has more signal ceiling to work with and will be less likely to drop the call. Also, it will use somewhat less transmit power, and your battery will last somewhat longer.
Making it longer with some sort of extension is worse than useless; it actually degrades the signal. If the antenna is exactly one wavelength long and is exactly perpendicular to the impinging waveform, it will pick up essentially no signal at all.
When it reaches one and a half wavelengths, signal strength is again maximized, but for physical reasons it's a bit lower than the strength with a half-wavelength antenna. (The physical reason is that the antenna is not an ideal conductor.)
[stolen directly from the CDMA FAQ
This assumes that cellphones can give you braincancer of which there is NO peer reviewed evidance.
:-) There is some evidance that mobile phone use can improve your memory but that's about it. Mobile phones have not been proved to be safe but then this will never be possible. It has been proved that the dangers are far less than the dangers of using a mobile phone whilst driving which kills many many people every day.
(they certainly can give you headaches;) not from the phone though speaking to the inlaws can cause this
This makes the antenna bigger. That means that the phone will send the braincancer waves to a bigger part of your brain, don't it? The size of the antenna does change its performance but a larger antenna can mean either a performance gain or a performance loss. A simple antenna wants to be 1/4 of the wavelength of the signal it is transmitting. Either bigger or smaller will reduce its performance. You are also missing a very important point. An improvement in the antenna means that the signal driving it can be reduced so as to save battery life. The signal strength generated by a mobile phone is adjusted to be as weak as possible so as to just make a reliable connection. Therefore the radiated output from the phone will be the same.
And it will be more difficult to shield the antenna because the outside of the phone will be a complete antenna. Mobile phone shields do not work. The phone simply increases the signal strength to compensate for any changes any so called shields provide. Transmission measurements in lab conditions have shown that shields make no difference at all.
Also a larger antenna doesn't neccesarely mean that it's better. Correct. However a larger antenna "could" be better.
I believe that for every wavelength there's an optimal size (if I remember correctly). The ideal length for a 1/4 wavelength antenna used on a mobile operating at 900MHz is 75mm. However, there are other options apart from 1/4 wavelength antennas.
wot no sig
since noone has posted it yet, i guess my karma-whoring is as good as any ..
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Good question!
A resonant antenna, cut to exactly half a wavelength, has some advantages but it's not a necessity.
The advantages are simpler circuit design, because it looks like a pure resistance and doesn't confuse the amplifier, and in theory a simple radiation pattern.
In practice the pattern will depend on everything in the environment, so good antenna testing is Very Difficult. Take all claims with a grain of salt until you hear that the antenna has been tested on an expensive antenna test range by experienced people.
When you're dealing with small fractions of a wavelength longer is better. For very short antennas, only a small fraction of the RF leaves as radiation before it's lost as heat from electrical resistance. "Longer is better" means "longer is more efficient".
BTW you can take advantage of how antennas are affected by nearby objects. If you're in a fringe area, try standing right next to your car, with the base of the antenna level with the roof line. Circle around the car until you're in the right alignment with the cell tower for further optimization.
Fred KC7YRN
Longer does not necessarily mean bad, or good.
Antennae do have to have certain characteristics to resonate and therefore radio a signal effectively, but like many things in life, there is more than one way to do this. It all comes down to the length of the antenna relative to the wavelength of the signal.
There are various "good" ratios of antenna length to wavelength. And the larger the antenna the better provided that the fit the "good ratio" models.
Nope.
The frequency of an antenna is determined by its' size and the speed of current flow in the material (among other things). The "tuning" of an antenna is dependent on what fraction of a wavelength (at the frequency of interest) is present on the antenna element(s) at one time. This is where you get the terms quarter-wave, half-wave, etc.
A measure of the effectiveness of an antenna is the "capture area". This is the effective size of the antenna. The conductivity of the material is important here - the better the conductor, the smaller the antenna can be made. (actually, some research shows that a superconducting antenna could be infinitessimally small, and still give the capture area of a full-wave antenna.)
There are a zillion variables in antenna design, and it seems like voodoo, but the net effect is that you can change a bunch of parameters, including the size, and end up with many different antenna configurations tuned to the same frequency.
- The Sigless Wonder
I design cellphone ICs for a living, so I can tell you that this could potentially be a "big deal". Reason is that high gain antennas mean you can either get longer range OR you can get the same range at a lower power.
If the PA (power amp) in the phone was connected to a high gain antenna, and did not have to put out as much power to reach the cell tower, that translates directly into a major power savings (the PA is one of the dominant power drains). Power savings means I don't need as big of a battery in the phone, which means I can shrink the battery and make the phone lighter and smaller and (very importantly) cheaper. Phones that are lighter and smaller sell better, this means $$$ for anyone who can make it work.
And of course when the company makes $$$, that means big bonuses for all us working in the trenches, which gets back to the "big deal" part..
He didn't say it doesn't work, he said it doesn't feel right, and I agree. I want what I'm talking into to be in front of my mouth, not over on the side of my face. Besides which, it seems that these small phones unconciously causes people to talk louder, to the point where many people on cell phones are almost shouting, to the great annoyance of all around them.
"The question of whether a computer can think is no more interesting than that of whether a submarine can swim" -EWD
There was a widely reported study (in the US anyway) about radiations of various cellphone and their possible connection to brain cancer. This report was also broadcasted on 60 minutes or 20/20 or Dateline (one of those news magazine, forgot which).
And essentially, it came out that the Motorolla Startacs were the best because the the flip design - the antenna is at an angle, farthest from your head, and partially shielded by the part of the cellphone that flipped up (I don't think Motorolla designed this phone thinking about brain cancer, they just got lucky). The worse were the Nokias where the antenna is straight up on top of the phone and so when you talk on the phone is close (if not touching your head).
I guess what I am getting at is that the original poster definetely has a point. If you make the whole casing of the cell phone the antenna, wouldn't that potentially be bad? It's one think to have radio wave all over the air, it's another to stick your head on the emitter.
...and eye cancer [com.com] [com.com] (just to emphasize the rather ridiculous domain name:P). Although this study was a bit small (as the researchers say themselves), the results aren't too accurate. But the conclusion is that cellphone users are 3 times more likely to develop cancer of the eye.
0x or or snor perron?!