Ambiguity function and accuracy of the hyperbolic chirp: comparison with the linear chirp

In this study, the authors derive the ambiguity function (AF) of a narrowband and a wideband hyperbolic chirp. They calculate the second derivatives of the squared amplitude of the narrowband complex AF and use them to calculate the Fisher information matrix (FIM) of the estimators of the target range and velocity. The FIM is then used to calculate the Cramér–Rao lower bounds (CRLBs) of the variance of the estimators and to carry out an analysis of estimation performance and a comparison with the case of a linear chirp with a rectangular and a Gaussian amplitude modulation. The analysis and the calculations of the CRLB are also extended to a train of hyperbolic chirps. Results corroborate that at narrowband the hyperbolic chirp is less Doppler tolerant than the linear chirp and show that the hyperbolic chirp provides a comparable measurement accuracy to the linear chirp. Results at wideband corroborate the superior Doppler tolerance of the hyperbolic chirp with respect to that of the linear chirp.