Good Question. iPhone 6 series uses LDS Antenna . This Antenna is embedded in the upper and lower part of iPhone, which you clearly mentioned that iPhone back is in 3 parts. Center part is metal and upper and lower part ( in the shape of D ) is plaStic, these two D's contain Antenna.
for ifixit, One simple solution.
1. Remove Bcak cover in iPhone 5 and make the phone call - See if call is placed or no !!!
2. Remove Back cover in iphone 6 series and make the phone call - first check if the signals are available or no.
I tried both methods, could not place call on iPhone 6 with back cover removed.
This will confirm the Theory that RF Antenna is placed inside back cover in iPhone 6S.
I will be writing complete Article on this today itself at http://smartfonearena.com"
The antenna stripes are unsightly (stick out like a sore thumb), break the homogenous flow of the case form and look like grout on bathroom tiling. As an industrial designer, I can´t imagine that Apple include such design transgression as an indespensible aethetic design feature - no, they are there for constructional and functional reasons. These ugly stripes are probably necessary for adequate signal reception. If that´s the case though, than how do other manufacturers manange using far thinner, less obtrusive atenna stripes. The case Iphone 6 is beautifully thin and sleak, but the antenna strips break the sleakness, and are the reason why I won´t buy the iPhone 6. Rumour has it the iPhone 6S will retrain these blemishes - possibly because of tooling cost investment, or because that would mean admitting their quick and dirty compromise and styling mishap.
