Spanwise-periodic roughness designed to excite selected wavelengths of stationary cross-flow modes was investigated in a 3-D boundary layer at Mach 3.5. The test model was a sharp-tipped 14å¡ right-circular cone. The model and integrated sensor traversing system were placed in the Mach 3.5 Supersonic Low Disturbance Tunnel (SLDT) equipped with a 'quiet design' nozzle at the NASA Langley Research Center. The model was oriented at a 4.2å¡ angle of attack to produce a mean cross-flow velocity component in the boundary layer over the cone. Five removable cone tips have been investigated. One has a smooth surface that is used to document the baseline ('natural') conditions. Two had minute (20 - 40 åµm) 'dimples' that are equally spaced around the circumference, at a streamwise location that is just upstream of the linear stability neutral growth branch for cross-flow modes. The azimuthal mode numbers of the dimpled tips were selected to either enhance the most amplified wave numbers, or to suppress the growth of the most amplified wave numbers. Two of the cone tips had an array of plasma streamwise vortex generators that were designed to simulate the disturbances produced by the passive patterned roughness. The results indicate that the stationary cross-flow modes were highly receptive to the patterned roughness of both passive and active types. The patterned passive roughness that was designed to suppress the growth of the most amplified modes had an azimuthal wavelength that was 66 % smaller that that of the most amplified stationary cross-flow mode. This had the effect to increase the transition Reynolds number from 25 % to 50 % depending on the measurement technique. The application of the research is on turbulent transition control on swept wings of supersonic aircraft. The plasma-based roughness has the advantage over the passive roughness of being able to be adaptable to different conditions that would occur during a flight mission.