中文摘要：

在天波超视距雷达中，舰船等慢速目标的频谱通常靠近强大的海杂波谱，检测难度大，在短相干积累条件下，回波频谱的多普勒分辨率降低，进一步增加了目标检测难度。目前的海杂波抑制方法主要是循环对消法，但是传统的循环对消方法仅通过傅里叶变换后最大谱线来估计频率，频率估计精度不高，杂波残留严重，而且容易将目标信号也对消掉。针对该问题，提出了一种改进的循环对消算法，该算法中，首先给出了短相干积累下海杂波频率的高精度估计算法，利用最大的3根谱线进行插值来对粗估计得到的频率进行校正，从而精确估计海杂波频率，在此基础上估计时域的海杂波信号；为了避免将目标信号也对消掉，进一步给出了海杂波的频率界限，只在杂波界限内进行海杂波循环对消；与传统算法相比，所提算法能够对海杂波参数进行高精度估计，从而减少了对消过程中剩余杂波的能量，有利于舰船目标的峰值显露，而且杂波频率界限的使用能够避免将目标信号对消掉，提高了目标的检测效能。仿真和实测数据处理结果均表明，与传统循环对消法相比，所提算法能用更少的对消次数凸显出舰船目标，而且残留杂波能量更低。

英文摘要：

In sky-wave over-the-horizon radar system,it is difficult to detect ship because the spectrum of the ship target is very close to the strong ocean clutter.In addition,short coherent accumulation which re-duces the doppler spectrum resolution makes the detection even more difficult.Currently,the main ocean clutter suppression method is the cycle cancellation algorithm.But the traditional clutter cancellation algo-rithm estimates the clutter frequency only by the maximum spectrum line of Fourier transform,the estima-tion accuracy is low,which results in severe clutter residual,and thus the target signal is easy to eliminate. To solve the problem,a modified clutter cancellation algorithm is proposed in this paper.In the modified al-gorithm,we first give a precision clutter frequency estimation algorithm.The maximum three spectrum lines are used to make interpolation for correcting the coarse estimated frequency.Then the precision clutter fre-quency is obtained.On this basis,we can estimate the clutter signal in the time domain.To avoid cancelling the target signal,we give a sea clutter frequency margin in this paper.The cancellation only proceeds in the margin.Compared with traditional cycle cancellation algorithms,the proposed algorithm can get more accu-rate clutter parameter and reduce the energy of the residual clutter among the cancellation.This is beneficial for detecting the peak of target and performance improvement.Simulation demonstrates that the proposed al-gorithm have better clutter cancellation performance than the traditional ones.