Motivated by the extraordinary modulation capability of the electromagnetic (EM) metasurface technique, a time-modulated metasurface-assisted moving target jamming method is proposed for the synthetic aperture radar (SAR) in this article. A time-modulated metasurface with real-time and flexible manipulation characteristics for the reflection phase of the EM wave under both normal and oblique incidences is designed, fabricated, and measured, respectively. It is capable of achieving composite phase modulation, which combines the advantages of the cosinusoidal-phase and subsection-phase modulations. Based on the designed metasurface, a spectral distribution with a series of discrete harmonic frequency components with varied frequency offsets and amplitudes can be formed. Furthermore, the composite phase modulation signal generated by the time-modulated metasurface is applied to interfere with the ground moving target indication (GMTI) for the SAR system, and the jamming effect of the metasurface on the moving target detection is analyzed in detail. The validity of the proposed jamming method is verified through theoretical analysis, metasurface modulation measurements, and SAR-GMTI experiments. Theoretical analysis and experimental results demonstrate that the adoption of the time-modulated metasurface modulation technique allows for the generation and detection of multiple discrete false moving targets with varying azimuth spacings and amplitudes for the victim SAR-GMTI system. The proposed method achieves effective moving target jamming and deception, expanding the application scenarios of metasurfaces in the field of radar electronic countermeasures.

Synthetic aperture radar (SAR) is an advanced radar system capable of high-resolution imaging of targets under all-weather and all-day conditions. Therefore, effective jamming against SAR imaging systems is an important application scenario for achieving stealth and camouflage in modern information warfare. In this paper, a novel jamming imaging architecture based on the time-modulated metasurface is proposed capable of realizing two-dimensional (2D) jamming and camouflage for SAR imaging systems. Firstly, a dual-polarized and conformal time-modulated metasurface is designed, fabricated, and measured, respectively. A high degree of freedom in the manipulation of scattered waves is fully verified under the flat and conformal states of the designed tunable metasurface. On this basis, using this electromagnetic metasurface as the hardware foundation, a 2D multiple phase sectionalized modulation signal model is established and generated by the metasurface to create 2D and highly realistic false targets, achieving camouflage and jamming of protected targets against SAR imaging. The proposed method is thoroughly validated utilizing simulated SAR data and satellite RadarSat-2 data, demonstrating its efficiency, flexibility, and high deception capabilities. These findings establish a general paradigm for the application of time-modulated metasurfaces in novel information electronic warfare.

Metasurfaces have shown unparalleled controllability of electromagnetic (EM) waves. However, most of the metasurfaces need external spatial feeding sources, which renders practical implementation quite challenging. Here, a low‐profile programmable metasurface with 0.05λ₀ thickness driven by guided waves is proposed to achieve dynamic control of both amplitude and phase simultaneously. The metasurface is fed by a guided wave traveling in a substrate‐integrated waveguide, avoiding external spatial sources and complex power divider networks. By manipulating the state of the p‐i‐n diodes embedded in each meta‐atom, the proposed metasurface enables 1‐bit amplitude switching between radiating and nonradiating states, as well as a 1‐bit phase switching between 0° and 180°. As a proof of concept, two advanced functionalities, namely, low sidelobe‐level beam scanning and Airy beam generation, are experimentally demonstrated with a single platform operating in the far‐ and near‐field respectively. Such complex‐amplitude, programmable, and low‐profile metasurfaces can overcome integration limitations of traditional metasurfaces, and open up new avenues for more accurate and advanced EM wave control within an unprecedented degree of freedom.

It is a challenging task to design a passive jamming method capable of both high fidelity and flexibility against synthetic aperture radar (SAR) imaging. Motivated by recent advances in the electromagnetic metasurface technique, a novel subsection-shift-Doppler-frequency jamming method based on the phase-tunable metasurface is proposed for the SAR system. Inspired by the realistic interference effects of the shift-frequency and segmented modulations, the proposed method flexibly imposes the subsection-shift-Doppler-frequency modulation on the SAR echo by the phase-tunable metasurface loaded with varactor diodes, which is designed to realize the continuous and real-time phase modulation through an external control system. Consequently, multiple false targets with flexible and controllable azimuth positions and verisimilar topological structures are generated instead of the protected target after receiving and processing the jamming signal by the victim SAR system. The influence of the phase-tunable metasurface modulation parameters on the jamming imaging effect is derived in theory. Simulations and experiments on satellite RadarSat-2 data are performed to verify the effectiveness of the proposed method. The theoretical analysis and experimental results show that the proposed method achieves the jamming imaging performance with high fidelity, high flexibility, low zero power, and low cost, effectively combining the advantages of traditional active and passive jamming.

Ground moving target indication (GMTI) in the synthetic aperture radar (SAR) system enables high-resolution, all-weather, and all-day imaging and detection of moving targets, posing a significant threat to high-value moving targets. Inspired by the flexible modulation capability of the electromagnetic metasurface technique, a cosinusoidal phase modulation jamming method based on tunable metasurfaces against the SAR-GMTI system is proposed in this paper. Firstly, the cosinusoidal phase modulation signal model generated by the tunable metasurface is investigated and discussed. Benefiting from the continuous phase control as well as flexibly adjustable modulation index and modulation frequency of the cosinusoidal phase modulation, the jamming signal with multiple false moving targets can be effectively constructed with a small phase variation. This characteristic effectively broadens the operational bandwidth. Subsequently, a novel dual-polarized tunable metasurface based on varactors is designed and implemented to achieve continuous phase modulation of radar signals. Owing to the rotational symmetry of the back-to-back open-ring resonators, the proposed metasurface enables independent and flexible control of two orthogonal polarizations. On this basis, the SAR-GMTI jamming performance of the cosinusoidal phase modulation with different modulation indices and modulation frequencies generated by the designed tunable metasurface is comprehensively analyzed theoretically and experimentally verified. It indicates that the high-quality SAR-GMTI jamming performance with high fidelity and flexibility can be achieved by appropriately adjusting the values of the modulation index and the modulation frequency, generating and detecting multiple false moving targets with different azimuth positions and large amplitudes at low SCNR while ensuring a small phase range.

Liquid crystals (LCs) are a kind of anisotropic materials with tunable dielectric properties in the microwave frequency band, which is of great significance for designing reconfigurable microwave devices such as beam-steering antennas, tunable phase shifters, or filters. Accurate characterization of the dielectric properties of LCs is crucial for designing and optimizing reconfigurable microwave components. In this article, a method for characterizing the dielectric properties of LCs is proposed based on epsilon-near-zero (ENZ) metamaterials. The measurement device is first designed using a waveguide-based ENZ structure. When LC-materials under tests (MUTs) are filled into the coupling tunnel, the strong electromagnetic intensity within ENZ metamaterials is fully utilized to sensitively detect the transmission response. In addition, biased circuits and preconditioned alignments are also designed and integrated to extract complex dielectric permittivities of anisotropic materials. Particularly, due to the metallic structure of the measurement device, a temperature control system consisting of a sensor and heating device can effectively and precisely control LC-MUTs’ temperature so that dielectric responses of LC-MUTs under different temperatures can be obtained. On this basis, according to the measured transmission parameters, the perturbation method is used to calculate complex dielectric permittivities of LC-MUTs. A prototype is fabricated and tested to verify the method. Complex dielectric permittivities of two LC-MUTs are extracted at 1.9 GHz, which verifies the effectiveness of the method. Note that the dielectric properties of a powder sample are also investigated using the same device, demonstrating the universality of this method. This work provides an alternative method for accurately measuring the complex permittivity of solid, liquid, and powder dielectric materials.