A novel reconfigurable polarization conversion method based on a metasurface turned by PIN diodes is proposed herein. The proposed metasurface consists of one layer of a dielectric and two layers of metal surfaces. When the diode is in an OFF-state, a wideband linear to circular (LTC) polarization converter is realized. The results show that the metasurface can achieve LTC polarization conversion in the frequency range of 11.8-24.1 GHz, and the axial ratio (AR) reveals that the 3-dB bandwidth is approximately 68.5%. When the diode is in the ON-state, a dual-band linear to linear (LTL) polarization converter is realized, with the 3-dB bandwidths of 10.5-13.9 GHz and 17.7-27.2 GHz, achieving a polarization converter ratio (PCR) greater than 90%. The dc bias circuit of the PIN diode is etched on the reflectance surface. Therefore, no additional feeding lines are introduced, which can decrease the impact on the active metasurface; this metasurface has practical applications in microwave communication systems.

In this paper, metasurfaces are designed, fabricated and experimentally demonstrated to transmit and receive a mixed-mode orbital angular momentum (OAM) vortex wave. Firstly, the theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce the mixed-state vortex wave. Then, simulations and near-field scanning experiments are performed to verify that mixed-state vortex waves can be generated and received by using metasurfaces. The receiving experiments for mixed-mode OAM beam are conducted in the near-field zone, covered frequency band from 4.5 GHz to 7.0 GHz. In transceiving experiments, the TX is the proposed reflective metasurface generating the mixed-state OAM wave (P = 2, l₁ = 1, l₂ = 2), which is composed of square loop elements. The RX is an OAM receiving metasurface composed by crossed dipole elements, which can receive OAM mode l = 1 in vertical polarization but OAM mode l = 2 in horizontal polarization. Experimental results show that mixed-state vortex waves can be detected, received and separated by pure OAM-mode transmitting and receiving reciprocal metasurfaces. The proposed method paves an effective way to generate and detect the OAM vortex wave of mixed modes for microwave wireless communication and detection applications.

This letter proposed a method to achieve angular selectivity of electromagnetic waves. Based on odd-mode resonant frequency selective surface (FSS), we can obtain varying frequency responses under different incident angles and polarizations. Angular selectivity for a given angle can be achieved at a fixed frequency. To further improve the angular selectivity, quarter-wave stacks principle is used to design the odd-mode FSS into angular selective surface (AGSS) with several bilayers. Multi bilayers AGSSs are analyzed and compared which indicates that our proposed method can effectively achieve angular selectivity from 20 to more than 70 for TE or TM polarizations. A 6-bilayer AGSS with perfectly transmission angle at 30 under TE polarization has been measured and the measurement agrees well with the simulation which further verifies the feasibility of our method.

In this article, we proposed a harmonic-absorbed frequency selective rasorber (HA-FSR). It consists of a non-resonant frequency selective surface (FSS) with inductive square loops, capacitive patches, and resistive sheet-based absorbers. The non-resonant FSS is of harmonic-suppression (HS) feature, which is free of spurious harmonic transmission bands up to three octaves of the main passband. We introduced resistive sheets on both sides of the HS-FSS to perform wideband absorption. Full-wave simulated and measured results both show that the proposed HA-FSR owns main passband with -3-dB bandwidth of 3 GHz at the X-band and -10-dB absorption band from 20 to 30 GHz. The frequency range of harmonic-absorption covers from around two to three octaves of the passband. The proposed HA-FSR can be applied in electromagnetic (EM) shielding and low-observable platforms.

In this Letter, we present a cylindrical conformal holographic impedance metasurface for orbital angular momentum (OAM) generation. The conformal holographic metasurface is designed by establishing the element library and deducing the formula of holographic tensor impedance modulation. The feasibility of the scheme is verified by simulations and experiments. Simulated and experimental results are in good agreement with theoretical analysis. The results show that OAM vortex wave energy can be generated efficiently by a cylindrical conformal impedance metasurface, which can provide a reference for OAM communication and vortex radars with conformal devices.

A harmonic suppressed (HS) frequency selective rasorber (FSR) based on square loops resonators and resistive-film sheets is presented in this paper. The frequency selective rasorber is designed by cascading the band pass FSS and broadband absorber together which owns a main pass band at center frequency of 8GHz, with harmonic transmission windows suppressed and out-of-band reflection absorbed from 12GHz to 26GHz. Lossless FSS with band pass response and lossy absorber with broadband absorption are analyzed by equivalent circuit model respectively. The frequency range of harmonic suppression covers three octaves of main pass band frequency. Besides, the measured results agree well with the simulated ones. The proposed harmonic suppressed FSR could be used as radome in enhancing anti-interference performance of wireless communication system and improving stealth performance of radar platform.