Effect of Cross-Correlation on the Ambiguity Function in FMCW MIMO Radars

Radars based on combinations of multiple-input multiple-output (MIMO) and continuous frequency modulation (FMCW) technologies are being actively investigated. FMCW MIMO radars with slow inter-symbol modulation of the initial phase in the transmitting elements and inter-pulse accumulation in the receiving elements have a significant advantage due to the significantly reduced computational complexity. However, such systems have a number of disadvantages, one of which is the strong influence of correlation characteristics of the signals used on the spatial ambiguity function (AF). In this paper, we build a mathematical model of MIMO FMCW radar with 16 transmitting and 16 receiving elements and show the results of the study of the influence of cross-correlation distortions on the spatial AF for three types of modulating signals: Legendre polynomials, Walsh-Hadamard codes and Zadoff-Chu sequences. It is shown that without introduction of additional phase compensations of the received signals unacceptable distortions of AF for velocities, for velocities from 20% of the range occur.