The mainlobe jamming suppression technique is one of the key techniques of radar electronic counter- countermeasure (ECCM). In the view of multistatic radar, the interference signals received with different view angles would be highly coherent, on the contrary, the target echoes would be independent due to the radar cross section (RCS) of target would randomly fluctuate as the variation of view angle. As a consequence, After the interference signals have been aligned, a steering vector can be found of interference signals, the energy of the interference signals will be concentrated in a single-rank subspace whereas the energy of the target echo signals will be scattered throughout the whole signal space of the multistatic radar. By exploiting this phenomenon, a new mainlobe interference suppression method for multistatic radar is proposed. In this method, the projection matrix is trained based on the time domain sampling data. The interference signals received by multiple node radars with different view angles can be effectively suppressed through the noise subspace projection operation. Then, a general likelihood ratio test detector used for the residual signals after projection operation is derived. The results of simulations indicate that the proposed method can effectively suppress various kinds of mainlobe jamming and improve the detection performance. Furthermore, this method is adaptive to the variation of the interference pattern and the geometric configuration of the node array.

In a distributed multiple-radar architecture, the spatial scattering properties of targets can be utilized to counter active deception jamming effectively. When the cooperative detection is performed, the difference in spatial scattering property makes the Hermitian distance of a false target considerably different from that of a physical target. The Hermitian distance of a false target increases with the raise of jamming-to-noise ratio, whereas the one of a physical target obeys an identical Beta distribution for all signal-to-noise ratios, which leads to the former much greater than the latter, especially in high jamming-to-noise ratio. Making full use of the difference, a novel method is proposed based on the Neyman-Pearson lemma to discriminate physical and active false targets in this paper. The proposed method overcomes the dependence of the available method on the prior information about the jamming environment. What's more, the proposed method can keep a constant misjudgement probability for physical targets and discriminate targets effectively in one pulse repetition interval. The theoretical analysis and simulation verify the feasibility and validity of the proposed discrimination method.

In a distributed multiple-radar architecture, the spatial scattering properties of targets can be utilized to counter active deception jamming effectively. When cooperative detection is performed, the available method to discriminate active false targets needs to know the precise jammer location, and its performance will suffer significant deterioration with little location error. Aiming at the problem, we propose a novel method to discriminate false targets based on Hermitian distance. The difference in spatial scattering property leads to the difference in the Hermitian distances of different target combinations. The Hermitian distance between two false targets is much greater than that between two physical targets or that between a physical target and a false target, especially in high jamming-to-noise ratio. Based on the difference, hypothesis testing is performed to discriminate false targets. The proposed method does not require any prior information about the jamming environment and can discriminate the targets effectively in one pulse repetition interval. Moreover, the proposed method can restrict the upper bound of the misjudgement probability for physical targets. The theoretical analysis and simulation verify the feasibility and validity of the proposed discrimination method.

Due to the silent operation of the receiver station in a multistatic radar system, it is difficult for the jammer to generate the cooperative active deception target for the multistatic radar system. Making use of the spatial diversity property, a data level fusion method is proposed to counter the active deception jamming in this paper. According to the spatial correlation difference in physical target and active false target motion states, the deception velocity of the physical target, which is obtained by the radial velocity of each receiver, obeys the Gaussian distribution with zero mean, and the one of the active false target obeys the Gaussian distribution with the mean being its true deception velocity. Based on this fact, the active false target and physical target are discriminated by the deception velocity testing. The proposed deception velocity-based (DVB) method can keep a constant misjudgment probability for physical targets and discriminate active false targets effectively, especially in large deception velocity cases. The simulation verifies the feasibility and validity of the proposed discrimination method. Moreover, the proposed method can be combined with the location information association method to enhance the ability to discriminate the range–velocity joint deception of false targets.

The orbital angular momentum (OAM) of a vortex electromagnetic wave (VEW) has gained attention as a newly explored information carrier. OAM modes provide vortex azimuth resolution, which is a new degree of freedom (DOF) in radar application. Due to the special characteristics of the vortex azimuth domain, VEW shares compound Doppler information of two-dimensional (2D) speed. This paper proposes a 2D target velocity estimation method for VEW radar. The Doppler effect of VEW is first analyzed. Based on the relativity of tangential speed and OAM mode, a pulse-by-pulse OAM mode-changing strategy is designed. Then, a modified Radon–Fourier transformation (RFT) is proposed to estimate the compound Doppler frequency while range migration is compensated. In addition, decoupling and ambiguity-solving procedures are applied to the compound Doppler frequency estimation to obtain tangential and radial speed estimations separately. According to the simulation analyses, the effectiveness of the proposed method is verified.

Within a complex sea or ground surface background, multipath signals are strongly correlated or even completely coherent, which leads to signal cancellation when conventional optimal beamforming is performed. Aiming at the above problem, a coherent signal-receiving algorithm is proposed based on oblique projection technology in this paper. The direction of arrival (DOA) of incident signals is estimated firstly by the space smoothing-based MUSIC method. The composite steering vector of multipath coherent signals is then obtained utilizing the oblique projection matrix constructed with the estimated angles. The weight vector is thereby derived with the minimum variance distortionless response criteria. The proposed oblique projection-based beamformer can receive the multipath coherent signals effectively. Moreover, the proposed beamformer is more robust and converges to optimal beamformer rapidly without aperture loss. The theoretical analysis and simulation verify the validity and superiority of the proposed coherent signal beamformer.