Abstract—Through-the-wall radar (TTWR) systems designed for detecting, locating, and tracking humans are plagued by harsh clutter scenarios caused by the variety and abundance of furniture elements within the antenna’s field-of-view. This paper investigates the signatures of indoor clutter using radar cross section (RCS) and linear depolarization ratios (LDRs) in order to implement clutter suppression algorithms. The paper focuses on the analysis of common individual and composite pieces of indoor clutter for TTWR. The characterization of the wideband spectral properties for indoor clutter elements is accomplished using finite difference time domain (FDTD) techniques. Using FDTD, the spectral characteristics of clutter elements are obtained over a wide range of frequencies, different polarizations, and aspect angles. We compare and contrast the RCS responses between the different objects for analysis and use in TTWR. RCS results obtained from the simulations are compared to experimental data using a network analyzer and reasonable agreement is obtained. Clutter signatures are also compared to those of humans in order to design appropriate waveforms for maximizing the signal-to clutter ratio (SCR) in TTWR systems.