When you touch an antenna conductor, it “de-tunes” the radiating element, usually lower in resonant frequency. The effect becomes more pronounced the higher in frequency you go.
You’re not really “shorting” anything out in the sense that something is going to blow a fuse - you’re effectively hanging a big, lossy lump of wet noodle off the end of the radiating element.
I’m rather surprised not only that this wasn’t found in testing, but that it made it through design. Most all of my RF work and studies were at HF to VHF frequencies, and having the user’s sweaty palm or fingers in contact with the radiating element would have been a no-no even at 150MHz - never mind up around 1.9 Ghz.
One thing that would be interesting is to see the difference between 850/1900 Mhz regions and 1900-only regions with this test.
Yeah, I was thinking you’re essentially taking a diversity antenna set and shorting the middle of the two antennas together through your hand - that will play all kinds of havoc with the impedance! Icky!
Just a few mils of polycarbonate over the antennas would solve the problem, but then the pretty outside is ruined. Form should follow function, not the other way around.
The reason this problem made it through usability testing was exposed by the $5000 prototype phone that Gizmodo paid for. Apple, not wanting anyone to know iPhone 4 even existed, dressed the prototypes up in cases that made them appear to be iPhone 3GS’s. The cases had the additional effect that they never allowed the band around the phone to be touched by the user’s hands.
This is an epic fail on Apple’s part.