An electronic device contains circuitry such as radio-frequency transceiver circuitry and antenna structures that are coupled using transmission line paths such as coaxial cable paths. A coaxial cable is mounted within an electronic device housing cable mounting structures. The coaxial cable has a meandering portion that forms a service loop. The cable mounting structures includes grooves that receive the meandering portion of the cable. The grooves may be formed within a molded plastic body. Patterned metal may be formed on the surface of the molded plastic body using laser-based processing techniques. The cable in the meandering portion may have a segment in which an outer cable conductor is exposed. The patterned metal on the molded plastic body may short the exposed outer conductor to the electronic device housing or other ground structure.