Anti-jamming MTI radar using variable pulse-codes

Abstract

A pulsed Doppler radar is vulnerable to advanced repeat-back jamming techniques. Rapidly advancing technology producing inexpensive, high performance commercial off-the-shelf (COTS) components enable the construction of an electronic countermeasure (ECM) system capable of exploiting this vulnerability. This thesis addresses this threat by examining the nature of this vulnerability and developing a modification to the pulsed Doppler/MTI radar system. Pulsed Doppler radar systems use pulse compression waveforms such as pseudonoise (PN) coded binary phase-modulated sequences. Repeat-back jamming listens, stores, and repeats back the radar's transmitted signal to block out all other return signals. If a different PN-code is used for each pulse, the radar receiver will be minimally affected by the jamming. However, a varying PN code creates range sidelobe variation that degrades the integrated signal-to-clutter ratio by a factor of 1/N2 where N is the code length. This severely limits the ability to perform Doppler and Moving-Target Indication (MTI) processing for clutter suppression on the radar return. To recover this performance loss several receiver filtering and digital signal processing techniques are tested. PN code selection for optimum filter performance is explored resulting in a 7-dB signal-to-clutter performance recovery for a 32-bit code. Digital pulse compression, matched filtering, and adaptive digital equalization filtering methods are applied to the radar return to equalize differences created by variable PN codes. Different equalization algorithms with various subsets of PN-codes are presented and simulated with data sets modelled after existing radar systems. Successful correction reduces clutter, minimizes the performance degradation to MTI due to variable pulse-codes, and resists some types of DRFM jamming.