Spectral characteristics of mixed micro-Doppler time-frequency data sequences in micro-motion and inertial parameter estimation of radar targets

Time variation of micro-Doppler (mD) frequency is an important representation of target's micro-motions and intrinsic attributes in radar signals. For free rigid targets consisting of multiple scatterers, mixed mD time-frequency (TF) data sequences based on two-dimensional TF distributions of mD signals demonstrates effectiveness and simplicity to estimate targets' micro-motion and inertial parameters. In this study the authors further explore the feasibility of the estimation method by studying the spectral characteristics of the mixed sequence. The construction of mixed mD TF data sequence is introduced, and then the analysis of its spectrum is conducted with the help of mathematical derivation and simulations. It is found that one of observation angles plays a leading role in relative amplitudes of spectral components, and could accordingly determine the optimal radar observation region for given micro-dynamic targets. It could contribute to the proper placement of radar station, and help identify some desired spectral components accurately in the blind condition for the purpose of parameter estimation of micro-dynamic targets.