Phase Coded Costas Signals for Ambiguity Function Improvement and Grating Lobes Suppression

In this paper, a novel radar signal is proposed. It is based on a modification of Costas signals obtained by increasing the frequency separation of Costas frequency hops beyond the orthogonality condition. Indeed, Costas codes are well known for their good Range-Doppler properties. Their orthogonality condition states that frequency separation between frequency hops of the Costas code should be at most equal to the inverse of bit duration of the code. Increasing frequency separation beyond this condition is sometimes needed in radar applications. However, this leads to the appearance of grating lobes near the main temporal lobe of the autocorrelation function. The originality of the proposed approach, in this paper, consists in proposing a modification of Costas sub-pulses in order to overcome grating lobes problem. Indeed, we show that when introducing Phase coding in the sub-pulses, grating lobes are lowered significantly. The study is carried out for several phase codes. The proposed code design is validated through computer experiments.