Explanation Behind How Antenna is Designed in Mobile Phones

It is worth stepping back a moment and asking the question, “Why are the antennas placed where my hand is MOST likely to cover it?”  It’s a fair question.

The FCC puts strict limits on the amount of energy from a handheld device that may be absorbed by the body.  We call this Specific Absorbtion Rate, or SAR.  In the olden days, when I walked ten miles to school in three feet of snow, uphill in both directions, cell phones had pull-up antennas.  This allowed the designer to use a half-wave antenna variant, and put the point of maximum radiation somewhat away from the users cranium.  Of course, most people did not think it was necessary and kept the antenna stowed.  Motorola’s flip phone acutally had a second helical antenna that was switched into place when this was the case.  But, more importantly, SAR rules were not yet in effect.

Flip phones became yesterday’s style, and phones were becoming more monolithic.  Some phones, like the early Treo, kept the antenna in the traditional location at the top of the phone, near one edge, but reduced it to a short stub.  Whips became stubs, stubs became bumps, and finally antennas were embedded into the rectangular volume of the phone.  The trouble was SAR; if you left the antenna at the top, the user was now pressing it into their head, insuring lots of tissue heating.  Enter the bottom-located cellphone antenna.

Just about every cell phone in current production has the antenna located at the bottom.  This insures that the radiating portion of the antenna is furthest from the head.  Apple was not the first to locate the antenna on the bottom, and certainly won’t be the last.  The problem is that humans have their hands below their ears, so the most natural position for the hand is covering the antenna.  This can’t be a good design decision, can it?  How can we be stuck with this conundrum?  It’s the FCC’s fault.

I’m a concerned about ’tissue heating’ mentioned in the article. Is it something to worry about?

Posted via email from owrange JUICENESS

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