In this paper, we introduce a precise real-time 3D indoor localization concept using a combination of the MISAS (multilateral inverse synthetic aperture secondary radar) approach and SMCM (sequential Monte Carlo method). The synthetic aperture approach is a promising locating technique with effective multipath suppression. However, its practical use is restricted by the huge computational load of the reconstruction algorithms. We use a weighted-particle set -which we reduce subsequently by resampling -to represent the PDF (probability density function) instead of the highly complex, standard, grid-based approach. Simulation runs and experiments, carried out with a 5.8 GHz FMCW secondary radar system with a bandwidth of only 140 MHz, show that a robot TCP (tool center point) can be localized in 3D in the mmrange using a few hundred particles and operating in a dense multipath environment. This novel extension is a promising solution for real-time, 3D MISAS localization applications.