Structure Optimization of Phase-Coded Sounding Signals

Pulse compression with a small sidelobe level is one of challenges in designing of modern radar, sonar or ultrasound imaging systems. It may be performed by means of matched filter, that is by correlating the received sounding signal with a stored replica of the transmitted signal. The advantage of the pulse compression method is the increase of the average transmission power while retaining the range resolution corresponding to a short pulse. Phase coding is one of the early techniques for pulse compression of radar signals. Polyphase sequences, which have low sidelobe levels, ensure an easily detectable peak in the output of a matched filter, in other words an easy detection of a received sounding signal. In this paper, an evolutionary algorithm combined with a local optimizer is used to search for polyphase codes with a small sidelobe level of an aperiodic autocorrelation function. The evolutionary algorithm is based on a floating-point representation and the Gaussian mutation is used to produce offspring for the next generation. The self-adaptation mechanism is used to control the mutation operator during the evolutionary process. This research demonstrates that optimization methods can effectively find polyphase sequences with low autocorrelation and seems to be very promising for the future research in area of computer optimization for polyphase codes synthesis.