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.

In this paper, an active polarization conversion metasurface (APCM) operating in the X-band (8–12 GHz) is presented. Active unit cells consist of three metal layers and two substrate layers. Anisotropic metal patches, positive-intrinsic-negative (PIN) diodes, and bias lines are integrated into the surface layer to form a chiral structure. A simple and efficient polarization conversion function is realized in this designed structure. The operating mode is switched between linear-to-linear (LTL) polarization conversion and linear-to-circular (LTC) polarization conversion by switching the loaded PIN diode. In the LTL polarization conversion state, the polarization conversion ratio of APCM is over 90% in X-band. Reflected wave circular polarization axis ratio <3 dB in 8–12 GHz when in LTC state. The proposed structure is verified by experimental measurements.

Electromagnetic (EM) metasurfaces comprising artificially designed subwavelength unit cells have drawn considerable attention due to the EM properties beyond the limits of natural materials. As one of the representative structures, active polarization conversion metasurface (APCM) is switchable by loading active components. It provides great freedom to manipulate the polarization state of EM waves. However, the current research mainly focused on the application of communication and paid less attention to the radar effect of APCM. APCM redistributes electromagnetic wave energy in multi-polarization channels, so it will have great application potential in polarimetric radar. Herein, based on the fully polarimetric radar one-dimensional high resolution range profile, the radar effect of time-modulated metasurface is studied. For this purpose, a method of target scattering mechanisms manipulation and a polarization-insensitive structure of APCM are proposed. The amplitude-phase joint modulation method is specifically analyzed in detail. The distance transformation and virtual multi-target phenomena are further discovered. Virtual targets along the distance dimension are generated in multi-polarization channels, while the scattering mechanisms of k-order targets are effectively manipulated. The relationship between the target scattering matrix and the modulation parameters is obtained. It may provide an effective method for the application of active metasurface in fully polarimetric radars.

Interrupted-sampling repeater modulation (ISRM) can generate multiple virtual target images by sampling and forwarding radar signals to confront the inverse synthetic aperture radar (ISAR). However, the repeating delay is unavoidable and the system is complex. Moreover, numerous works mainly discuss the ISAR image deception based on periodic modulation, and the modulation effect is relatively limited. Active frequency selective surface (AFSS) can perform intermittent amplitude modulation to the reflected signal by varying target reflectivity, thus, it can achieve the function of ISRM. In this paper, the possibility of AFSS applied in the multiple virtual target generation is discussed, and an ISAR image-modulation method is proposed. The radar signal is periodically modulated by varying target reflectivity, which is accomplished by the AFSS-loaded PIN diodes. On this basis, the AFSS modulating frequency is randomly varied in a slow time domain. When the modulation signal is processed by the ISAR system, the produced target image is unfocused and cannot be recognized by radar. Simulation results are utilized to demonstrate the effectiveness of the proposed method.

Time-modulated metasurfaces have attracted much attention due to their flexible manipulation of electromagnetic waves. Time-varying response leads to spread-spectrum and reallocation of energy. Thus, an amplitude-phase joint modulation (TAJM) method is proposed based on a time-modulated active polarization conversion metasurface (APCM). Taking radar high resolution range profile (HRRP) as the object, the distance transformation and multi-target phenomena are further discovered. The proposed method achieves a flexible manipulation of target amplitude and phase. The relationship between the modulation parameters and HRRP feature is studied. It is revealed that the absorption depth is the dominant factor for the energy distribution of TAJM. The method can be applied to multi-target generation and target feature manipulation.

Metasurfaces exhibit remarkable abilities to manipulate electromagnetic (EM) waves and have inspired many applications in communication and radar systems. Recent advancements in metasurface research have promoted the development of various low-cost and low-complexity methods for the modulation of radar target high-resolution range profiles (HRRPs). However, existing metasurface-based methods lack the capacity to achieve simultaneous and precise control over the quantity, positions, and intensity of scattering centers in the modulated HRRP. This article addresses the challenge and proposes a radar target HRRP modulation method utilizing multifrequency time-varying metasurfaces (MFTVMs). This method allows for precise customization of the quantity, positions, and intensity of false scattering centers in HRRPs, which enables flexible modulation of HRRPs. By incorporating frequency variation into temporal modulation, the method introduces an additional degree of freedom in metasurface control, thereby enhancing the modulation capabilities of metasurfaces without compromising the effectiveness of original modulation methods. The theoretical and experimental analyses presented in this article substantiate the validity of the method. Furthermore, the concept of introducing frequency variation into the temporal control of metasurfaces may inspire further research in harmonic manipulations and radar applications.