In a note to clients — as noted by MacRumors — KGI Securities analyst Ming-Chi Kuo says 2018 iPhones will feature upgraded liquid crystal polymer (LCP) antenna modules that will result in faster LTE transmission speeds. His note says:
Antenna design upgrade a key factor in anticipated boost to LTE transmission speed in new 2H18F iPhone models. As a LTE antenna FPCB material, LCP is superior to PI in properties related to high-frequency, thermal performance and moisture resistance. We predict 2H18 new iPhones will be equipped with two LCP LTE antenna modules same as iPhone X or more, but with higher specs to support 4x4 MIMO standards.
Previously Kuo has said Apple is expected to use Intel XMM 7560 and Qualcomm Snapdragon X20 modems in its next-generation iOS devices. This would enable faster LTE transmission speeds. Both of those chips support the previously mentioned 4x4 MIMO technology, compared to 2x2 MIMO in the current iPhone models.