Proposal Of Flat-Coaxial Cable Structure And Its Design Methodology Based On Fpcb Process For 5g Application

For 5G application, cable is essentially required for a low signal loss characteristic and immunity to the external noise inside a mobile product. A conventional coaxial cable can carry out such functions but there are critical disadvantages with using a cable. One is that interconnection of multiple signals in one cable structure is impossible, and the other is that automated assembly of a cable and a PCB is difficult. Consequently, these disadvantages restrict design flexibility of a product. Therefore, development of a new cable structure which overcomes these problems is necessary. In this paper, we propose a novel coaxial cable structure which uses a Flexible PCB (FPCB) process for foldable mobile device. This is the first cable structure with attributes including both a coaxial and a multiple channel. Since the proposed cable structure is flat and has a fixed form, automated assembly of a cable and a PCB could be made possible using a suction machine. We also propose a three-step cable design methodology for performance improvement. The first step involves design, fabrication, and measurement of the proto-type cable structure. The second step involves extraction of effective material characteristics of the proto-type structure. The third step involves signal integrity design and optimization with the proposed model. With the proposed methodology, estimated performance before fabrication is well correlated with the measurement at frequencies up to 20 GHz which includes the intermediate frequency (IF) of 5G application.