Superconducting NbN was produced on commercial carbon fibers and sapphire substrates by dc reactive magnetron sputtering. Uniform coating was achieved by spreading 9000 filaments into a strip located between two planar magnetrons facing each other. The conditions forB1 phase formation and homogeneous coating have been studied. Over a rather wide range of total pressures,pAr+pN2, the highest superconducting transition temperature was found for a nitrogen partial pressurepN2of about 0.05 Pa. In addition, tensile or compressive strains were produced in the NbN film on the carbon fiber as a function of bias. The NbN grain size was controlled in the range between 10 and 25 nm. Without a bias, the usual (111) preferential orientation of the grains was observed in the NbN film on the carbon fiber. The intensity ratioI200/I111could be controlled between 0.74 and 0.4. Under an increased bias, the lattice parameter grew from about 0.4385 to about 0.4395 nm. This behavior may be due to a variety of reasons. The superconducting critical currentsjcin a self‐magnetic field are about 105A/cm2for NbN on carbon fibers (C‐NbN) and about 2×106for NbN on sapphire (S‐NbN). Various microstructures and, to some extent, also mechanical defects are thought to be responsible for this difference. At 13 T, the correspondingjcvalues are 2×104and 105A/cm2for NbN films of 1‐&mgr;m thickness. The extrapolatedBc2(4K) values for C‐NbN are about 30–35 T, for S‐NbN about 25 T. The nucleation conditions for NbN depended strongly on the substrate; this was found to be true for the existence of theB1 phase with respect to gas composition, microstructure, and deposition rate. The analysis of the composition of the films, which was performed by Rutherford backscattering and scanning Auger depth profiling, revealed uniform compositions with approximately 1‐at. % carbon and approximately 0.1‐at. % oxygen contaminations.