A new concept of the coding phase gradient metasurface (CPGM) is proposed, which is constructed using the phase gradient metasurface as the coding elements. Different from the previous coding metasurface (CM), both the coding sequences and gradient phases in the coding elements are designed to manipulate the electromagnetic (EM) wave for the CPGMs, and thus the manipulation will be more flexible. As an example, wide-band, wide-angle CPGMs with zero and non-zero phase gradient based on Pancharatnam-Berry (PB) phase are achieved using the co-polarization reflection unit cells under circularly polarized (CP) wave incidence. Both theoretically calculated and numerically simulated scattering patterns of the designed CPGMs demonstrate the expected manipulations. Additionally, two kinds of random CPGMs with different phase gradients are designed for radar cross section (RCS) reduction, and the measured RCS reveals a good accordance with the simulation.

Metasurfaces have been extensively investigated to achieve radar cross section (RCS) reduction over a wide frequency band. In this paper, we propose the design of a novel metasurface with a transmission window within the wide RCS reduction band. The function of this metasurface is similar to rasorbers, whereas the mechanism behind the wideband RCS reduction is scattering cancellation rather than absorption. To this end, the ideal reflection and transmission properties of the metasurface unit cell are firstly revealed. And then an anisotropic unit cell composed of multilayered metallic patterns is designed to obtain the desired reflection and transmission properties. The bottom layer is composed of the typical patch-grid-patch bandpass frequency selective surface, which allows for high transmission in the transparent window and also behaves as a metallic-like reflection sheet in the RCS reduction band. Two metasurfaces, with checkerboard and aperiodic configurations, respectively, were designed, fabricated and measured, as a proof-of-concept demonstration. A good agreement between the simulations and measured results provides a solid verification for our design. The results here provide an alternative method to open a transparent window within the RCS reduction band and may find potential applications in stealth radomes.

Spin light manipulation based on chiral metasurfaces is a striking hotspot that has intrigued huge attention. Circular dichroism, a unique phenomenon of chiral atoms/molecules, has been regarded as another auxiliary dimension for guiding electromagnetic waves, which has been explored in the field of artificial material sciences yet a challenging issue. Here, a generic strategy based on dynamic chiral meta-atom for revealing strong circular dichroism as well as applicable electromagnetic functionality is proposed in microwave regime. We demonstrate a dynamic metasurface that enables the fully independent holograms reconstruction for one circular polarization or the other at the active operating state. On the other hand, the electromagnetic scattering is realized for lowering observable backward reflection at the passive state. Numerical simulation and experimental verification are conducted to manifest the feasibility. It is expected that the proposed strategy can be applied to broaden the horizon for dynamic chiral meta-devices and may find applications in information encryption, anti-counterfeiting, and other dynamic systems.

In this paper, we propose the design of antennas with low radar cross section (RCS) based on dispersion engineering of spoof surface plasmon polaritons (SSPPs). The antenna consists of a feeding monopole and a SSPPs guiding structure placed vertically on a metal ground. By comprehensively engineering the weak and strong dispersion regimes of the SSPPs structure, the cut-off frequency of SSPPs can be made close to the upper operating frequency of the feeding monopole. In this way, the SSPPs structure serves as a high-efficiency radiator in the operating band and as a broadband absorber out of band, leading to low RCS out of band. As an example, a C-band antenna with low RCS in X band was designed, simulated and measured. Both the simulation and experiment results show that the antenna can radiate in C-band, with average gain 6dB and fractional bandwidth 28%. In order to evaluate the RCS reduction performances, a 5×5 antenna array was fabricated and the mono-static RCS was measured. The measured results show that the mono-static RCS is reduced by more than 10dB in the whole X-band (8.0-12.5GHz), with a maximal reduction above 30dB. The design method provides an effective alternative to low-RCS antennas.

In this paper, a low radar cross section (RCS) patch antenna is proposed, which is realized by engineering dispersion property of metamaterial absorbers (MAs). Dispersion curve of the MA consists of weak linear regime with low insertion loss and asymptotic non-linear regime with strong absorption. By changing geometric parameters, dispersion property of the MA can be engineered, so that cut-off frequency is shifted freely, as well as the strong absorption band being changed. Thus, if cut-off frequency of the MA is very close to the upper bound frequency of a patch antenna, the patch antenna will obtain polarization-independent low RCS property out of band or in-band cross-polarized and out-of-band co-polarized low RCS properties by replacing the radiation patch with the modulated MA. For verification, a C-band patch antenna with RCS reduction performance in X-band is designed, fabricated and measured. Both the simulated and measured results agree well and verify that the antenna achieves average gain about 5 dB in 7.2∼7.7 GHz. To assess the RCS reduction performance of the proposed patch antenna, we fabricated a 5×5 antenna array. The measured results indicate that mono-static RCS of the array is decreased by more than 10 dB in the entire X band for co-polarized and cross-polarized wave normal incidence compared with metallic plate with the same area.