Yong Yang

Sea clutter exhibits complex, time-varying statistical characteristics due to variations in radar operational parameters and sea surface conditions, which severely degrade the false alarm control performance of conventional constant false alarm rate (CFAR) detectors. To achieve effective false alarm suppression without compromising detection performance in time-varying heterogeneous sea clutter, this paper proposes a dual-radar fusion detection scheme for two independent X-band staring radars deployed at different positions, featuring a cascaded architecture of signal-level fusion and false alarm discrimination. In the first stage, a relatively low threshold is adopted for signal-level fusion detection under the Rayleigh clutter assumption, thereby enhancing the target detection probability. Subsequently, a two-stage discriminator suppresses false alarms generated in this preliminary stage by exploiting the feature differences between targets and false alarms in pulse continuity and instantaneous frequency stability. Comparative evaluations on four datasets of real sea clutter measurements under sea state 3 demonstrate that the proposed scheme achieves superior detection performance and more robust false alarm control than existing multi-radar fusion detection methods, while exhibiting favourable adaptability to variations in wave height and wave direction.

Direction finding methods with single-channel time-modulated arrays (TMA) have simple hardware structures, which can significantly reduce the cost of passive direction finding systems. However, the existing methods did not consider the polarization factors in signal propagation and array configuration. When the polarization mismatch occurs between the incident signal and the receiving array, the accuracy of direction estimation decreases substantially. To solve this, a joint estimation approach is proposed to estimate the parameters of incident direction and polarization for an arbitrary polarized radiation source, using single-channel alternating polarization time-modulated arrays (AP-TMA). By extracting multi-harmonic signals and employing polarization projection weighting, robust direction finding and polarization estimation performance are achieved. The proposed approach is validated through simulations and experiments.

To address the vulnerability of single-polarization deception jamming and simply modulated dual-polarization jamming to discrimination by dual-polarization radars, this paper proposes a deception jamming method based on joint fast–slow-time polarization modulation (FSPMJ). First, in the slow-time domain (across multiple pulses), the polarization azimuth of the jamming signal is designed according to the target’s polarization ratio distribution. Subsequently, with the target polarization degree as the optimization objective, the polarization phase difference of the jamming signal is solved using an interior-point optimization algorithm, establishing the initial polarization state for each pulse. This process is iterated to design the polarization state for the first half of each pulse. Then, in the fast-time domain (within a single pulse), a polarization state orthogonal to the pre-generated first-half state, is constructed to serve as the polarization state for the latter half of each pulse. Finally, the effectiveness of the proposed method is validated through combined simulation and measured data using a Support Vector Machine (SVM) algorithm. Results demonstrate that compared to single-polarization deception jamming and existing polarization-modulated jamming, this method reduces the false target discrimination rate of dual-polarization radars by 35.4% without requiring complex target scattering matrices.

In this paper, a comprehensive overview of radar detection methods for low-altitude targets in maritime environments is presented, focusing on the challenges posed by sea clutter and multipath scattering. The performance of the radar detection methods under sea clutter, multipath, and combined conditions is categorized and summarized, and future research directions are outlined to enhance radar detection performance for low-altitude targets in maritime environments.

Radar target echoes undergo fading in the presence of specular reflection, which is adverse to radar detection. To address this problem, this paper proposes a radar detection method that uses a single transmitting antenna and three receiving antennas. The proposed method uses the maximum absolute value of the difference in the radar received signal power among the three receiving antennas as the test statistic. First, the target echo in the presence of specular reflection is analyzed. Then, selection of the required number of radar antennas and the heights at which they must be situated are discussed. Subsequently, analytical expressions of the radar detection probability and the false alarm probability are derived. Finally, simulation results are presented, which show that the proposed method improves radar detection performance in the presence of specular reflection.

The parameter estimation in the forward scatter radar (FSR) network is the focus of attention in the radar field. In this letter, a parameter estimation method using the crossing time difference and the Doppler rate is proposed in the FSR network. The continuous position and the velocity estimation of the uniform moving target are realized. Then, the factors affecting the estimation accuracy are theoretically analyzed, including parameter measurement error and receiver locations. The effectiveness and the adaptability of the method are validated through Monte Carlo simulations. Compared with the parameter estimation method only based on the crossing time, higher accuracy can be achieved, and fewer receivers or transmitters are needed, so it should be easier to be deployed in the real application.

Combined sky‐wave and surface‐wave monostatic high‐frequency (CSSM‐HF) radar is a new type of mono‐static high frequency (HF) radar that uses multiple combined propagation modes of skywave and surface wave to detect targets. However, the detection range of different propagation modes partially overlaps, which results in multiple mode echoes from one target. To track the target in the presence of multi‐mode echoes, a new multi‐mode target tracking algorithm is proposed in the study, which uses the detection range as a priori knowledge. In CSSM‐HF radar, the possible propagation mode of the target echo is related to the position of the target itself. Therefore, the study uses the detection range simulation results as a priori knowledge to construct a propagation mode judgment module to effectively improve the calculation efficiency and performance of the tracking algorithm. The simulation results show that the proposed algorithm can effectively track the target in the presence of multi‐mode echoes and the tracking performance of the target with lower abscissa speed is better. In addition, the mode judgment module directly affects the performance of the algorithm. The tracking performance will be reduced when the output of the mode judgment module has an error mode.

The characteristics of the radar returns for unmanned aerial vehicle (UAV) are useful for radar detection and classification of the UAV. In this study, the authors carried out an experiment in an anechoic chamber to measure the fully polarimetric echoes of a fixed‐wing UAV in X‐band. With the measured data, they analysed the distribution of the radar cross‐section of the UAV. They also analysed the distributions of the phases and polarisation ratios of the UAV returns in various polarisation modes. They found that the radar cross‐sections of the fixed‐wing UAV in HH and VV polarisation modes obey lognormal distribution. The radar cross‐sections of the UAV in VH and HV polarisation modes obey Weibull distribution. The means of the radar cross‐section in co‐polarisation modes are 8–10 dBsm higher than those in cross‐polarisation modes. The phases of the UAV echo in HH, HV, VH and VV polarisation modes are uniformly distributed within 0 and 2 π . The amplitudes of the polarisation ratios of the UAV echo are well fitted by lognormal distribution.

This article addresses the polarization scattering matrix (PSM) estimation problem of a point-like moving target. For the alternating measurement scheme, the radial displacement of the target would generate an additional phase error between two columns of the measured target PSM. Due to the decline in the performance of the traditional pulse integration (PI) method when the target is moving, the pulse compensation (PC) is discussed. Then, methods of measurement selection (MS), measurement selection with three polarizations (MS-3-Pol), and measurement selection with two nonorthogonal polarizations (MS-2-Pol) are proposed. By the estimated Doppler frequency, PC can be applied for the uniform moving target. The performance of PC degrades significantly when the target's velocity is inaccurate or unknown. However, methods of MS, MS-3-Pol, and MS-2-Pol can still be used. As the three methods do not require any a priori information about the target motion, they are suitable for situations when the target is in nonuniform motion. The MS method is sensitive to the structure of the measured PSM. Due to the three polarizations (3-Pol) scheme, MS-3-Pol is robust even for a target with small cross-polar scattering parameters. Furthermore, by the assumption of reciprocity, the 3-Pol can be simplified into a new scheme with two nonorthogonal polarization. Then, MS-2-Pol is able to estimate the moving target PSM, even if the cross-polar echoes of the target are close to zero. Compared with PI and PC, the performance of the proposed methods is irrelevant to the state of the target motion. Furthermore, when the signal-to-noise ratio is greater than 10 dB, the polarized correlation coefficients of MS-3-Pol and MS-2-Pol can be above 0.95. All the conclusions presented in this article are validated by the experimental results.

In order to obtain the target polarization scattering matrix (PSM), a simultaneous polarimetric measurement scheme is designed in this letter. As a complete measurement scheme, one of its hardware implementations is analyzed, and the methods of PSM estimation are proposed. Instead of employing the linear frequency modulation (LFM) waveforms with opposite slopes, the proposed scheme uses the amplitude-modulated LFM waveforms with a unitary slope. Then, the PSM estimations can be obtained from the measurements. The experimental results demonstrate that the proposed scheme has a potential advantage for the PSM measurement. When the signal-to-noise ratio is greater than 24 dB, the means of polarized correlation coefficients keep higher than 0.9. All these conclusions are verified by numerical experiments.