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This communication proposes a novel dual-band shared-aperture antenna hybridizing Fabry–Perot cavity antenna (FPCA) and folded reflectarray (FRA), which operates at both sub-6 GHz and millimeter-wave bands with a large frequency ratio of 1:4.6. This antenna is composed of two substrates, with metasurface printed on the upper substrate and reflector layer printed on the lower one. The metasurface works as partially reflective surface (PRS) of FPCA at the sub-6 GHz band while acts as polarization grid of FRA at the millimeter-waveband. Thus, the FPCA and the FRA are able to share the same aperture with high aperture reuse efficiency. A composite feed structure combining waveguide with microstrip patch antenna is used to feed at two bands, implementing shared-aperture feed. This antenna achieves high gains at two bands without complicated feeding networks. A prototype operating at 5.4 and 25 GHz bands is designed, fabricated, and measured to verify the idea. [ABSTRACT FROM AUTHOR]

In this article, a flexible, stretchable, and dynamically tunable attenuator based on coplanar waveguide (CPW) and graphene is proposed. Soft silicone elastomer and serpentine metal structure are used to realize the flexible, stretchable, and biocompatible characteristics of the CPW. A graphene sandwich structure (GSS) is placed on the upper surface of the CPW to dissipate the electromagnetic wave, achieving the dynamically adjustable characteristics of the stretchable attenuator. When the surface impedance of the GSS is tuned by applying a proper bias voltage, the simulated and measured results reveal that the attenuation tuning range is dynamically tuned from 4–11 dB with a low reflection below −10 dB. In addition, the fabricated attenuator is simultaneously optimized to work at conditions of the normal state, 180° bending and 130% stretching, with acceptable changes between insertion loss and return loss up to 6 GHz. The attenuator covers the medical frequency band of 2.4–2.483 GHz and the 5th generation (5G) communication frequency band of 3.5–3.8 GHz, which demonstrates that the attenuator has potential applications in stretchable electronic systems. [ABSTRACT FROM AUTHOR]

This letter presents a novel dual-band and shared-aperture Fabry–Perot cavity antenna (FPCA) with high aperture efficiency (AE) and high port isolation, which operates in both S- and C-bands with a frequency ratio of 1:1.45. This antenna is composed of a partially reflective surface (PRS), a frequency selective surface (FSS), and a ground plane. A microstrip patch working at 3.45 GHz and a dipole working at 5 GHz are acted as primary radiator, respectively. To form two separate FP cavities, the FSS layer shows passband characteristic for low frequency and stopband characteristic for high frequency. Since two resonant cavities share the same PRS layer, the utilization rate of the proposed antenna has been significantly improved. This scheme can be used to design shared aperture antenna with any frequency ratio. To verify this design concept, an antenna prototype is designed, fabricated, and measured. The measured results demonstrate that the proposed dual-band shared-aperture FPCA has −10 dB impedance bandwidth of 3.42–3.47 and 4.94–5.05 GHz with the peak gain of 13.7 dBi (at 3.45 GHz, 77% AE) and 16.8 dBi (at 5 GHz, 74% AE), the isolation between two ports is better than 30 dB, which agrees well with the simulated ones. [ABSTRACT FROM AUTHOR]

In this article, a dynamically tunable graphene-based absorber in Ku-band is proposed for the first time, the center frequency of which can be continuously tuned while maintaining an excellent absorption performance. It consists of a periodically patterned graphene sandwich structure (GSS) and periodic patches printed on the substrate backed with the ground. The periodically patterned GSS is directly deposited on the top surface of patches. By using the external bias voltage, the proposed absorber can provide a dynamically tunable operating frequency from 13.9 to 16.4 GHz, in which the absorptions remain above 0.92. To theoretically investigate the performance of the absorber, an equivalent circuit based on transmission-line is derived. We fabricate and measure some samples to experimentally verify the dynamical frequency tunability of the graphene-based absorber, which has never been really achieved before in microwave frequency. A good agreement between simulation and measurement is acquired. The whole thickness of the absorber is equal to $0.06\lambda $ , which provides a path forward for the realization of a dynamically tunable and ultra thin absorber. The design strategy can generally be applied to other wavelength region applications such as mechanical deformation and bolometric detector. [ABSTRACT FROM AUTHOR]

This communication presents a Fabry–Pérot resonator antenna (FPRA) with the dual-band dual-orthogonal circular polarization (CP). The whole FPRA consists of a linearly polarized (LP) microstrip patch antenna and a chiral metamaterial (CMM) superstrate. The LP microstrip antenna serves as the feed system, while the CMM superstrate has the function of polarization transformation. The CMM also works as a partial reflective sheet to form an FPRA. The ray-tracing method in the circular base is introduced to describe the mechanism of this type of FPRA. Furthermore, the procedure of controlling the frequency ratio of two bands is discussed as well. An antenna prototype is fabricated to validate the simulated results. In the frequency band from 7.24 to 7.36 GHz, the proposed FPRA produces right-handed CP wave. However, left-handed CP wave is achieved when the frequency ranges from 7.96 to 8.14 GHz. The realized gains reach 12.98 dBic at 7.28 GHz and 13.25 dBic at 8 GHz, respectively. [ABSTRACT FROM AUTHOR]

Metasurfaces, a new class of planar metamaterial, are attracting intensive attention due to their exceptional abilities to manipulate the electromagnetic waves. In this paper, a metasurface based on graphene ribbons is developed to realize beam reconfiguration of microwaves. With the use of chemical vapor deposition-grown single-layer graphene or multilayer graphene (MLG), a reflection response with the phase difference of $\pi $ and a relatively large amplitude can be achieved. Different reflection angles of arranged arrays demonstrate the possibility of designing binary-phase-based metasurface, such as coding metasurface using resistive materials. Besides, the direction of the reflected beam can be changed by varying the sheet resistance of MLG with a fixed structure, combined with the electrically connected configuration of the proposed structure, this result further shows the great potential of graphene in developing switchable devices for beam reconfiguration at microwaves. [ABSTRACT FROM AUTHOR]

Radar-absorbing materials are used in stealth technologies for concealment of an object from radar detection. Resistive and/or magnetic composite materials are used to reduce the backscattered microwave signals. However, nontunable characteristics or the required complex structure hampered the application of these materials. Here, multilayer graphene-based frequency selective surfaces (MLGFSS), which reach a size of 150 mm $\times $ 150 mm, are designed and fabricated. By properly changing the growth temperature of MLG using the chemical vapor deposition approach and designing the pattern of graphene layer, the impedance matching condition can be satisfied at different frequencies. As a result, two kinds of absorbers with different working bandwidths are realized. The performances of the proposed absorbers are analyzed using full-wave simulation and are also tested with experimental results. Our method of fabricating large-area MLGFSS avoids the direct contact between the stencil mask and graphene, and guarantees the integrity and quality of patterned graphene structure. A good agreement between simulation and measurement results demonstrates that such ultrathin MLGFSS is very useful in the design of graphene-based functional devices at microwave frequencies. [ABSTRACT FROM AUTHOR]

In this paper, a dynamically tunable substrate-integrated-waveguide (SIW) attenuator using graphene is first presented. Two graphene sandwich structures are placed inside an SIW, which serve as conductivity-tunable E-plane septum. By applying biased voltage to the graphene, the attenuation can be dynamically changed; meanwhile, the reflection can still keep at a relatively low level. A closed form of the attenuation is also proposed, and the mechanism of the attenuator is theoretically analyzed in detail. Furthermore, a prototype operating from 7 to 14.5 GHz has been fabricated and measured. Both the theoretical calculation and the numerical simulation results have a good agreement with the experimental results, which present the attenuation ranges from 2 to 15 dB with a stable 7.5-GHz wideband while the bias voltage changing from 0 to 4 V. [ABSTRACT FROM AUTHOR]

This communication presents a 32\,\times\,32 high-gain patch array antenna fed by the substrate integrated waveguide (SIW) structure at W-band. The array antenna consists of two layers to achieve a compact topology, which allows for mass production using a standard PCB fabrication process. The wideband feeding network is placed in the bottom layer while the radiating patches are on the top layer. This configuration also resolves the trade-off between gain and bandwidth of conventional SIW array antennas. Measured gain of the 32\,\times\,32 antenna array is within the range 28.81–29.97 dBi in the working bandwidth of 91–97 GHz. Measured impedance bandwidth covers the same frequency band for \vert S 11 \vert < -10~dB. The cross-polarization of the antenna array is less than 40 dB at the beam direction. Good agreement between the simulated and measured results validates our design. [ABSTRACT FROM PUBLISHER]