Abstract: Transmission cable assemblies and methods for suppressing common-mode currents on a transmission cable are provided. The transmission cable assembly may include a transmission cable and at least one trap fitted on the transmission cable. Each trap may include a first coil and a second coil in opposite helical directions and assembled to allow the transmission cable to insert through. The first coil and the second coil form a resonant circuit for reducing common-mode currents on the transmission cable. When there are multiple traps fitted on the transmission cable, they are spaced apart along the longitudinal axis of the transmission cable and an insulating component is placed between every two adjacent traps. The designs can make the trap filters smaller and lighter in weight while effectively reducing the impact on the local radiofrequency (B1) field.