Switchable active frequency selective surface (AFSS) absorber/reflector can work in opposite scattering state and be widely applied in the stealth field. At present, abundant researches on material design have been conducted to obtain excellent electromagnetic (EM) properties. However, there are few studies on the modulation effect of switchable AFSS absorber/reflector on the EM wave. In this paper, a time-domain digital-coding AFSS absorber/reflector is proposed to manipulate the spectral distribution of harmonic. The accurate control of each harmonic is achieved through AFSS modulating parameters. Then, a simple controller based on FPGA is designed. By coding “0” and “1” elements with controlled sequences, the AFSS can be switched flexibly in both absorbing and reflection states. On this basis, the imaging characteristics of time-domain digital-coding AFSS absorber/reflector are further analyzed, and distance transformation phenomena are described in detail. The SAR experiments are performed to demonstrate the required function of distance transformation.

Micro-Doppler characteristics have been widely utilized to discriminate the space targets. In this paper, the micro-Doppler parametric model (mDPM) is presented to fit the micro-Doppler characteristics of cone-shaped space targets. Then, the genetic algorithm-general parameterized time-frequency transform (GA-GPTF) method is proposed to estimate the parameters of mDPM accurately. Additionally, the ratio of the two parameters of mDPM is verified to be directly related to the physical attribute of scattering centers. It can be applied to discriminate the type of scattering centers quantitatively. Finally, the electromagnetic simulation and anechoic chamber experiment verify the accuracy of mDPM and the effectiveness of the scattering center discrimination method.

The discovery of electromagnetic (EM) metasurfaces has significantly advanced the free manipulation of EM waves. Further, the harmonic phenomena based on time-modulated metasurfaces (TMMs) have received much attention in communication and radar detection applications, which can reduce the efficiency of radar target detection. However, existing research on time-varying metasurface has neglected its potential to manipulate the scattering characteristics of polarized radar targets. When a linear polarization wave is incident on a metasurface, it will be reflected into two orthogonal polarization states of EM waves, thus directly affecting the polarized scattering of the target. Active Polarization conversion metasurfaces (APCM) can manipulate the polarization of electromagnetic waves, aligning well with polarimetric radar. In this work, a dual-polarization radar target feature manipulation (Pol-TFM) method based on APCM is proposed, which enables manipulation of the harmonic and energy distribution of radar echo signals in multiple polarization channels. Through this processing, virtual targets generated by harmonic effects become observable on the dual-polarized high resolution range profile (HRRP). This method also allows for the position manipulation of the virtual targets. Finally, echo signal experiments are conducted in dual-polarimetric channels to verify the effectiveness of the proposed method.

The accurate extraction of micro-Doppler (m-D) curves is crucial for target recognition for space targets. However, the strong overlap of m-D curves and the noise disturbance of multi-component non-stationary signals in the time-frequency domain make it a great challenge to separate these curves using conventional algorithms. To address this problem, a curve extraction algorithm for multicomponent m-D signals based on the reassociation Viterbi algorithm (RVA) is proposed in this paper. First, the Viterbi algorithm is combined with an adaptive curve removal method for curve detection in a multicomponent m-D signal. Then, a two-step association method based on distance and velocity is presented to achieve correct curve separation. In addition, a variable threshold algorithm is introduced to extract both strong and weak components. Finally, the improved validity and robustness of the proposed algorithm have been verified by experiments compared to conventional methods.

This paper presents a comprehensive measurement and calibration methodology for full-polarization characterization of radar targets at sub-terahertz (THz) frequencies. A novel three-object polarization calibration technique is proposed to address amplitude and phase imbalances in the measurement system. The method is implemented using a sub-THz radar cross-section measurement platform with twist waveguides for polarization switching. Experimental validation in an anechoic chamber demonstrates the method's effectiveness, achieving phase mismatch within 20°, polarization isolation better than 15 dB, and co-polarization amplitude imbalance below 2 dB. The calibrated data's accuracy is further confirmed through Cameron decomposition, showing excellent agreement with theoretical predictions. This work provides a robust framework for precise polarization characterization in the sub-THz regime, with potential applications in radar target recognition and imaging.

Micro‐Doppler (mD) characteristics of the ballistic targets have attracted great attention due to the potential in target discrimination. However, current investigations mainly focus on blunt‐nosed cone and cone‐cylinder‐shaped targets. In practical applications, ballistic targets are always designed as the streamlined shape due to smaller aerodynamic resistance and lower detectability. In this Letter, the mD characteristics of streamlined ballistic targets are analysed. Owing to the unique mD signatures, the sliding scattering centre induced by the reflection from the streamlined curved surface is particularly focused. Finally, simulation results via the electromagnetic computation verify the correctness of the analysis.