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In this article, a tunable linear-to-circular polarization converter (LTCPC) in terahertz (THz) regime using the graphene transmissive metasurface is proposed, which is composed of two resonant layers containing the metal and graphene resonators separated by a dielectric spacer. The linearly-polarized wave with normal incidence can be transformed to the circularly-polarized wave. The operating band can be dynamically regulated in THz band by electrically controlling the Fermi energy (E f) of the graphene sheets rather than reforming the structures. The optimized result of axial ratio (AR) band which is less than 3 dB is located at 2.64-3.29 THz (the relative bandwidth is 21.92%) in the case of E f = 0.1 eV. The physical characteristics of graphene are explored and the relevant operational results of the presented LTCPC are elucidated in this article. Compared with the conventional LTCPC, our design provides a more effective implementation method for wide applications, and it offers a further step in graphene controllable devices.

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In this article, a VO 2 -based tunable omnidirectional circularly polarized (CP) antenna is designed. The proposed antenna combines copper and metamaterial VO 2 . By utilizing the characteristics of insulator-metal phase transition of VO 2 , we can change the length of the resonant branches to achieve tunable working bandwidth. The proposed antenna is composed of a modified floor loaded with VO 2 and copper resonant branches, a top patch with slits, and 14 shorting vias connecting the top path and bottom floor. Different from the traditional electric controlled antennas, antennas based on metamaterial VO 2 do not need to design complicated circuit structures and can be easily tailored by the external temperature (T). The simulated results illustrate that when T ≥ 68 C (state I), the proposed antenna has a 10-dB impedance bandwidth of 15.9% (2.09-2.45 GHz), and a 3-dB axial ratio (AR) bandwidth of 23.4% (2.04-2.58 GHz). When T < 68 C (state II), it has a bandwidth of 6.5% (2.38-2.54 GHz) with S 11 below −10 dB, and a bandwidth of 19.9% (2.39-2.92 GHz) with AR below 3 dB. K E Y W O R D S omnidirectional circular polarization, phase transition, tunable antenna, VO 2

In this article, a tailored coplanar waveguide (CPW) circularly polarized (CP) antenna is designed, whose operating band can be adjusted in a large range by the gravity field through rotating the antenna vertically. Due to the fluidity of liquid metal mercury, which is packaged in the antenna's glass containers, when the antenna is rotated, mercury will lead to different metal resonant units in different directions under the influence of gravity. This antenna utilizes CPW whose metal reflective surface and the main radiating patch are on the same side of the dielectric substrate. The dielectric substrate is made of FR4, and the metal radiation patch and the metal reflective ground are made of copper. Two metal branches separated from the main radiation patch are connected to the main radiating patch by a glass container. To verify concept of the design, equivalent prototypes have been fabricated and measured. The measured results are roughly consistent with simulated results within a reasonable error range. The measured results show that when the antenna turns 90° counterclockwise along the x‐axis (state I), the 10‐dB return loss bandwidth is 13.5% (4.54~5.2 GHz), and the 3‐dB axial ratio (AR) bandwidth is 13.8% (4.5~5.17 GHz). When the antenna turns 90°clockwise along the x‐axis (state II), the 10‐dB return loss bandwidth is 23% (3.73~4.7 GHz), and the 3‐dB AR bandwidth is 23% (3.73~4.7 GHz) within the antenna operating range. In the cases of two different working states, the proposed antenna can effectively cover the 5G communication band.