Complementary sequences with high sidelobe suppression factors for ST/MST radar applications

Under ideal conditions, complementary code pairs produce no sidelobes. In practice, sidelobes are produced, among other things, when the period of the Doppler frequency shift as well as the time of coherence of clear air turbulence are comparable (or smaller) than the interpulse period. The intensity of sidelobes increases with the radar operating frequency and becomes a real problem in the upper VHF and UHF bands. In this paper, a new technique for reducing sidelobes originating from atmospheric characteristics for clear air radar systems using pulse coding is presented. For this, a generalized analytic expression for a sidelobe suppression factor applicable to any number of binary code sequences is first derived. This is then used to develop the technique, which in the case of complementary codes consists of manipulating the order of transmission of the code sequences. For such codes, improvements in sidelobe suppression of the order of 80 dB on the VHF frequency band are obtained. The modifications required to implement the technique into existing systems are very few and simple.