Leaky coaxial cables are not only used for radio coverage but also for indoor positioning and navigation. For positioning with RF fingerprinting the received signal power levels at various positions are measured and stored in a radio map. The accuracy of this positioning method strongly depends on the reliability of the radio map. Therefore, the power level fluctuations have to be suppressed, to get a higher localization accuracy. With approaches like averaging the measured power levels by frequency, time, place and antenna polarization some improvement was achieved, but the reachable indoor positioning accuracy could not be used for practical application. In this paper constructive approaches are investigated to suppress power level fluctuations by using ferrite cores and variations of slot apertures.