In the HF ground-wave OTH radar

the movement of the radar brings about the spreading of the first order Bragg lines.It is difficult to pick up and measure the ship targets of the cover-up in the spread first order Bragg lines for the shipboard environment.In this paper

the causation of the spread spectrum are firstly analyzed

then it is suggested to use single null beam to pick up the ship targets and use pair null beam to detect targets direction.At last the method is simulated and the validity of detecting method of targets direction is attested for the HF ground-wave OTH radar.