Location estimation of a capsule endoscope in the gastrointestinal (GI) tract is a challenging task, as radio frequency signals encounter a high loss and highly dynamic channel propagation environment. In this paper, the possibility of using a radar system for capsule localization is investigated at frequencies of 2.4 GHz, 3.4 GHz, 4.8 GHz and 5.8 GHz respectively. Based on our theoretical analysis, the system at 2.4 GHz exhibits better performance. Therefore, in the next step a detailed analysis of the RF propagation in the human abdomen is presented with the aid of numerical simulations using Finite-Difference TimeDomain (FDTD) method. Our simulation results show that a radar system at 2.4 GHz can be considered for tracking the capsule if a high sensitivity receiver is deployed. In addition, we provide an in-depth study investigating the effect of antenna position and polarization on the received signal strength. The studies show that vertical polarization of the antenna outperforms other linear polarization because it provides better signal strength in the center of the human abdomen.