The iPhone antenna is the two plastic belts on the back of the mobile phone.
Nowadays, many mobile phones are starting to use metal shells. According to the principle of electromagnetic shielding, it is difficult for electromagnetic waves to penetrate the body surrounded by metal rings and metal shells, so in this case, the signal of the base station is not covered, but the mobile phone itself. IPhone 4 adopted the stainless steel frame and made the antenna in the same year. It also foreseen the plastic barrier to prevent electromagnetic interference between the two sides. However, due to the lack of plastic barrier, the antenna door finally appeared.
Later, apple added more plastic barriers to new products, and placed an ugly antenna barrier on iPhone 6 to ensure signal reception. The same situation appears on the HTC One M7.