In this communication, a millimeter-wave (MMW) pattern reconfigurable Vivaldi antenna utilizing graphene-based tunable resistor is proposed. First, a modified Vivaldi antenna with high front-to-back ratio is achieved by equal proportion slotting on the ground patch. Then, a pattern reconfigurable antenna consisting of a pair of back-to-back modified Vivaldi antennas with two graphene nanoplate pads symmetrically loaded on the feed line is proposed to realize dynamical manipulation of gain. By applying bias voltage from 0 to 4 V, the resistance of the graphene pad can be gradually reduced from 200 to 20Ω. Two slots located on the ground allow two graphene pads to be dc interruption for independent resistance control. By varying the resistance of two graphene pads, the radiation pattern of Vivaldi antenna can be manipulated from two opposite beams to a single beam. Finally, a prototype antenna centering at 30 GHz with a bandwidth of 16.6% is fabricated and measured, which realizes reconfigurable radiation beams at 90° and/or 270° with three states.

In this article, a novel class of dynamically tunable filtering attenuators with high selectivity and continuously tunable attenuation is proposed through the comprehensive design of graphene sandwiched structure (GSS), microstrip line, and half-mode substrate integrated waveguide (HMSIW). The GSSs are loaded on microstrip resonators to reduce the resonance intensity, which results in a valid attenuation in the passband. A co-design method of GSS, microstrip resonator, and HMSIW coupling structure based on the equivalent circuit model is proposed to minimize the impact of graphene on the selectivity of filtering attenuator. A transmission zero located on the upper band is also introduced to enhance the selectivity. By varying the bias voltage on GSSs, a controllable attenuation from 1.7 to 8.4 dB can be obtained over the operating bandwidth centering at 1.72 GHz while preserving good selectivity. It is worth mentioning that the out-of-band suppression of the proposed filtering attenuator is also reduced from 40 to 50 dB. Another tunable filtering attenuator based on microstrip short-ended resonators is also designed to verify the method. Finally, a prototype is fabricated and measured and the measured results are in good agreement with the simulation results.

A novel dual-polarized frequency-selective rasorber (FSR) using an omnidirectional planar resistor based on graphene flake is presented in this article. The FSR exhibits a low-loss transmission window above an absorption band. It consists of a lossy layer and a lossless bandpass frequency-selective surface (FSS). In the lossy layer, a central symmetric graphene-metal hybrid structure is formed by connecting four metal strip-based resonant circuits with a square graphene flake. A low insertion loss transmission band is obtained by removing the resistance out of the parallel resonant circuits. Moreover, equivalent circuits are utilized to demonstrate the working mechanism. The proposed FSR exhibits a good absorption performance from 8.15 GHz to 13.8 GHz, and a low insertion loss of 0.15 dB obtained at 16GHz. Finally, a prototype FSR is fabricated and good agreement between the simulated and the measured results is obtained. The FSR has further advantages of avoiding the process of welding multiple lumped resistors per unit, thereby greatly reducing the number of lumped components and improving the planar integration of the structure.

In this article, we present a via-based hybrid metal–graphene metamaterial absorber with miniaturized periodicity, broad absorption band, and large-angle radar cross Section (RCS) reduction. The unit cell of the absorber is composed of a cross-shaped graphene film, four metal arrow-shaped patterns, and four cylindrical vias. By extending the length of vias and folding the shape of the pattern on the top, the unit size of this proposed absorber is reduced greatly, while its absorption performance maintains. Furthermore, the adopted hybrid metal–graphene structure avoids loading multiple lumped elements, and the complexity and the cost of the fabrication are reduced by screen-printing technology. Because of the elements with miniaturized periodicity, the proposed absorber can shift the grating lobe (GL) out of the absorption band when illuminated by a large-angle oblique incident wave. A prototype absorber is fabricated and measured. The period of the proposed absorber is about $0.045\lambda _{L}$ at the lowest operating frequency. To the best of our knowledge, it is the smallest among the reported counterparts. Experimental results show that the absorber exhibits broadband absorption around 2.73~7.54 GHz and efficient RCS reduction with no GL under a large incident angle. The equivalent circuit analysis, full-wave simulation, and measurement results are in good agreement.

A novel transparent and broadband diffusion metasurface that is composed of digital coding elements is presented. A coding unit shares a symmetric circular quasi-Minkowski closed-loop shape that is capable of generating 1 bit coding (with two phase states of 0° and 180°) elements by using different geometric scales. To improve the optical transmittance of metasurface, the top layer of the coding elements adopts the metal rings with ultrathin linewidth with the optical transmittance of above 97% theoretically, whereas the bottom layer adopts hexagonal ring mesh metallic film with the optical transmittance of 95.4% and high electromagnetic interference (EMI) shielding effectiveness. Moreover, an optimized random distribution of coding elements is elaborately designed to realize diffusion patterns with numerous uniform grating lobes resulting in significant suppression of the backward peak energy level. Finally, a prototype diffusion metasurface is fabricated and good agreement between the simulated and the measured results is obtained. The results demonstrate a significant polarization-insensitive diffusion property with about 10 dB scattering reduction in a broadband from 10.5 to 19.5 GHz, reaching a fractional bandwidth of 60%, as well as show good scattering reduction properties for oblique incident waves. The proposed optical transparent diffusion metasurface has further advantages of opening up a new route for tailoring the exotic microwave scattering features with simultaneously high transmittance such as window and other transparent applications in visible frequencies and can be extended for imaging and communications.

In this paper, a multilayer reflective polarization conversion metasurface with both high frequency selectivity and low profile is proposed. The frequency selective polarization conversion metasurface (FSPCM) is composed of four metal layers separated by three substrates. The cross-shaped patch on the top layer is connected to the folded microstrip line on the bottom layer with two via holes through the circle slots inside two ground layers, which converts the linearly polarized electromagnetic incident wave into cross-polarized wave after reflection. The second-order response can extend to the third-order response by introducing a coupled half-wavelength microstrip resonator on the bottom metal layer, which achieves high frequency selectivity with a transmission zero and high polarization conversion rate (PCR) without increasing the thickness. The equivalent circuit analysis, structure simulation and experimental demonstration are conducted in detail, the frequency selectivity of the fabricated FSPCM at the lower and upper band-edge is 94 and 192 dB/GHz, respectively, PCR is more than 97% from 4.85 GHz to 5.12 GHz, and the thickness is only 0.028λ₀, where λ₀ is the free space wavelength at the center operating frequency. Our findings pave a new way for enhancing the anti-interference capability and electromagnetic compatibility in applications of communication system, microwave imaging and stealth technology.