Synthesis of Directional Modulation LFM Radar Waveform for Sidelobe Jamming Suppression

This study proposes a directional modulation linear frequency modulated (DM-LFM) waveform synthesis approach to enhance the sidelobe jamming suppression capacity in radar systems. The DM-LFM waveform expression is modeled with a transmit phase matrix in the phased array antenna. The DM-LFM waveform synthesis criterion is formulated to reduce the phase distortion and power loss in the desired beam direction and simultaneously maximize the mismatch between the transmit waveforms in the mainlobe and sidelobe jammer regions. Thereby, the DM-LFM waveform provides the beam with the freedom to scramble the radar transmit waveform toward the sidelobe. The transmit phase matrix is iteratively solved using a combination of the least ${P}$ -norm, the alternating direction method of multipliers (ADMM), and the limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) algorithms. Simulation results demonstrate that the DM-LFM has a moderate power loss of 2.7 dB and a minor phase error of 0.37° when using an eight-element phased array. In the jammer region, the peak level (PL) of the matched filtered output of DM-LFM is one order of magnitude lower than that of the traditional phased array (TPA). The sidelobe jamming suppression performance of DM-LFM improves, as the jammer region narrows and the number of antenna elements increases. The DM-LFM shows an excellent sidelobe jamming-resistant performance.