The range-dependence of clutter spectrum for forward-looking airborne radar strongly affects the accuracy of the estimation of clutter covariance matrix at the range under test, which results in poor clutter suppression performance if the conventional space-time adaptive processing (STAP) algorithms were applied, especially in the short range cells. Therefore, a new STAP algorithm with clutter spectrum compensation by utilizing knowledge-aided subspace projection is proposed to suppress clutter for forward-looking airborne radar in this paper. In the proposed method, the clutter covariance matrix of the range under test is firstly constructed based on the prior knowledge of antenna array configuration, and then by decomposing the corresponding space-time covariance matrix to calculate the clutter subspace projection matrix which is applied to transform the secondary range samples so that the compensation of clutter spectrum for forward-looking airborne radar is accomplished. After that the conventional STAP algorithm can be applied to suppress clutter in the range under test. The proposed method is compared with the sample matrix inversion (SMI) and the Doppler Warping (DW) methods. The simulation results show that the proposed STAP method can effectively compensate the clutter spectrum and mitigate the range-dependence significantly.

This paper creates a new hybrid Space-Time Adaptive Processing (STAP) algorithm that combines Direct Data Domain (D3) method and Space-Time Multiple-Beam (STMB) algorithm, which can effectively suppress discrete interference in the nonhomogeneous clutter environment. In the proposed hybrid algorithm, the D3 method is applied to process the discrete interference in the primary range cell, and the residual clutter is suppressed by the STMB algorithm. The performance of the proposed hybrid STAP algorithm is demonstrated in a simulation.

The double threshold detecting strategy is widely used for spatially distributed target detection in practical systems. However, the detector is limited in terms of robustness and effectiveness. In this paper, an improved double threshold detector is proposed that avoids these shortcomings. In the proposed detector, the energy in range cells that exceed the first threshold is accumulated and then the output of the accumulator is compared with the second threshold for detection. The threshold selection strategy is derived to guarantee the constant false-alarm rate (CFAR) property. A simulation shows that the proposed detector is superior to the conventional approach in terms of both robustness and effectiveness.