Understanding of sidelobe cancellation

Sidelobe cancellation （SLC） It is an effective measure of radar anti-jamming , The suppression of sidelobe interference is achieved by adding several auxiliary antennas near the main antenna .
The main antenna of radar is generally a strong directional antenna , The main lobe gain of the antenna pattern is large , The side lobe gain is low , And the main valve is generally very narrow , And the side lobe covers most of the space . therefore , For interfering signals , The probability of entering the radar antenna from the sidelobe is very high , In order to suppress interference , Usually, the sidelobe gain is very low , But when the radar is in a very strong active jamming environment , The interference signal may drown the target signal .
In principle , Commonly used in SLC All the secondary antennas are omni-directional antennas or weak directional antennas , And the gain is equivalent to the sidelobe of the main antenna , The wave path difference caused by the different spatial positions of each antenna , Therefore, the interference signal received by each antenna has a fixed phase shift , Use the interference signal received by each auxiliary antenna , Weighted sum through adaptive algorithm , Subtract from the interference signal received by the main antenna , Adjust the weight adaptively , Minimize the interference power of the main channel , Eliminate the interference .
The adaptive algorithm for solving weight value is generally divided into open-loop and closed-loop , The principle is to minimize the power difference between the main antenna and the auxiliary antenna , By minimizing the mean square error , When the mean square error of shaving is 0 when , The best weight vector can be obtained , The specific formula can refer to teacher chenboxiao's 《 Analysis and design of modern radar system 》 A Book .
In general, in practical engineering , Due to broadband interference, there will be different responses in different distance units , To cope with broadband interference , Achieve better cancellation performance , Each pulse will be segmented , Solve the weight value in segments , Cancel .
Personal understanding ：
In the abstract , The initial pattern of the radar is determined by the main antenna , The positions of the main lobe and side lobe are also determined by the design of the main antenna . When there is active interference , The simplest method is to design a zero point for the antenna pattern in the direction of the interference source , In this way, the interference cannot enter the interference main lobe signal from the side lobe .
But the main antenna pattern is fixed , So by adding the weighted sum of auxiliary antennas （ Beam forming ）, Form a negative beam in the direction of the interference source , Offset the sidelobe beam in the direction of the interference source , It realizes the function of setting zero point for the pattern .
Because the direction of interference source is random , And some mechanical scanning radar antennas have been scanning , So we need to adjust the weight coefficient adaptively , Update the zero point of the pattern in real time .