New quasi-complementary code sets for atmospheric radar applications

The basics of using low-autocorrelation binary sequences in high-resolution atmospheric radar experiments are briefly reviewed. An exact cancellation of correlation side lobes with repeated complementary code pairs is often not attained due to transmitter nonlinearities and due to poor coherence of atmospheric targets. Sulzer and Woodman (1984) have recently introduced quasi-complementary code sets (QCCS) of low-autocorrelation binary sequences, obtained by an extensive computer search, for which the side lobes nearly cancel on accumulation over the set. Improved performance of QCCS over complementary pairs has been confirmed in experiments with the Arecibo UHF radar. We report here an exhaustive computer search for a base set of 32-bit binary sequences with correlation side lobes at level 3. These codes are then combined in optimal QCCS of several even set sizes with a residual correlation side lobe level of 2, or 6 dB better than for a sample QCCS of 48 codes given by Sulzer and Woodman. A similar search for 64-bit codes, using a partial base set of ∼4000 codes with correlation side lobes at level 5 and 6, gives QCCS with a residual correlation side lobe level of 6.