A high-frequency data and/or power transmission system suitable for downhole use including signal/power couplers, transmission line segments and signal repeaters. Signals and power are/is transmitted between couplers and/or between couplers and repeaters by means of electromagnetic resonance coupling. In at least a portion of the system, the transmission line segments form parallel data paths and the repeaters provide crossover capability between the data/power paths, thereby significantly improving reliability. The invention also includes methods of transmitting data and/or distributing high-frequency power through a downhole transmission system including multiple data/power paths and multiple crossovers wherein a fault location in one data/power path is bypassed by routing data and/or power to a parallel data/power path by means of electromagnetic resonance coupling.
