Sidelobe Suppression in Pulse Compresssed Radar Signal

Abstract

Radio Detection And Ranging, RADAR, is a system that is used to detect and track a target at distant location with its other features (like velocity, direction etc.). The system uses various techniques to enhance its efficiency in terms of different physical parameters. Pulse compression technique provides the radar designers with an ability to combine the benefits of low power transmitters and the larger pulse wavelength to maintain the energy content of the pulse, in turn, the process elevates the range detection ability of high duration pulses and the resolution capacity of short pulses. To enhance the bandwidth of the high duration pulses so that better range resolution capability can be achieved, modulation in frequency and phase is done. Frequency or phase modulation is employed to a long duration pulse before it is transmitted and the received pulse is then passed through a filter to get its energy accumulated into a short pulse. Usually, matched filter is a common choice for pulse compression. Due to the high sidelobe peaks associated with the mainlobe in the matched filter output, which is simply an ACF of the input pulse, they have the possibility of masking the weaker targets near the stronger ones. So, the high sidelobes are needed to be suppressed to avoid such circumstances. Normally, the matched filter output has the sidelobe level of -13.5dB which can be improved by the use of the techniques like adaptive filtering, weighting through the use of windows etc. The windowing technique, besides suppressing the sidelobe also reduces the SNR which leads to reduction in rate of false alarm rate. A stepped frequency train of LFM pulses is an efficient method to enhance the overall bandwidth of the signal and maintaining the instantaneous bandwidth at the same time. But they are associated with the ambiguous peaks whose peak value is similar to the mainlobe peak and are also known as the grating lobes which have the potential of masking the smaller targets. So, it becomes necessary to suppress or nullify them by proper adjustment of the design parameters..