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A metasurface-based low-profile crossed dipole antenna with wide circularly polarized bandwidth for 2.45 GHz ISM band wireless communications is proposed and fabricated in this article. Consisting of four slit-loaded rectangular patches, the double-sided printing crossed dipoles are fed by a pair of vacant-quarter printed rings which circularly polarized (CP) radiation could be generated. With slits loaded, by properly combining the fundamental mode of the two inverted L-shaped dipole, the slot mode and extra resonance generated by the AMC surface, a wideband circularly polarized operation can be obtained. After optimization, the final design with an overall size of 0.44k 0 3 0.44k 0 3 0.1448k 0 at 2.4 GHz had measured a 31.6% (2-2.75 GHz) impedance bandwidth and 3 dB axial ratio bandwidths of measured were 23.2% (2.1-2.65 GHz), respectively. In addition, the antenna performed a small gain variation (7.0-7.5 dBic) and a front-to-back ratio (FBR) of over 25 dB across the whole CP region. K E Y W O R D SAMC, circularly polarized, low profile, wideband | I NT ROD UCTI ONNowadays, in the fields of electronic countermeasure and communication, circular polarized technique has been widely used. When two degenerate modes of equal amplitude and phase difference of 908 were excited, a circular polarization (CP) could be achieved. 1 To achieve CP radiation, several printed monopoles have been proposed.2-11 LP and CP operations were achieved by a multiband coplanar monopole antenna with the trapezoidal structure adopted in ref. Recently, with intensely studied in metamaterials (MTMs), the performance of the traditional CP patch antenna has been improved by utilized MTMs. Improvements of enhancements in bandwidth and an overall reduction in size were included. For an overall size of 0.77k 0 3 0.77k 0 3 0.06k 0 , a 3 dB AR bandwidth of 15% was achieved by a diagonal slot-loaded square patch over a 458-oriented reactive impedance surface (RIS).14 An artificial ground structure was applied in a truncated corner square patch in ref. 15, where an AR bandwidth of 20.4% and an overall size of 0.78 k 0 3 0.80 k 0 3 0.096 k 0 has been achieved. To achieve an overall size of <0.3 k 0 3 0.3 k 0 3 0.03 k 0 , MTMs-based single-feed CP patch antennas [16][17][18][19] have been implemented, but narrow 3-dB AR bandwidths (only 5% or less) were exhibited. In refs. 16,20,21, it proposed an AMC and has since been widely applied. Then, a wide CP operation were obtained, but significantly radiation performances and enhancing the bandwidth of and the size of an antenna could be both reduced by applying such surfaces.Int J RF Microw Comput Aided Eng. 2018;28:e21173.

This paper introduces an effective solution for improving isolation in linear antenna array. The array is composed of three-element E-plane single feed patch antennas (the overall size is 0.59 λ 0 × 1.02 λ 0), which are closely placed with approximately 0.037 λ 0 , where λ 0 is the free-space wavelength at 4 GHz. The decoupling structure consists of T-shaped and rectangular ring shaped defect ground structure (DGS) with six metal-vias. The decoupling mechanism is illustrated by investigating the current vector on the ground plane. The current distribution indicates that the decoupling structure along the outer edge of the radiation patch sever as coupling current converter to produce reverse current opposite to the direction of the ground coupling current, which transmits along the outer edge of the radiation edge. The measured results show that the enhancement in the isolation at 4 GHz is 10.8 dB for |S21|, 17.5 dB for |S23| and 16.6 dB for |S31|. After applying the decoupling structure, the 10-dB impedance bandwidth (3.95-4.04 GHz) of antenna 1 remains unchanged. Meanwhile, the 10-dB impedance bandwidth of the antenna, which is located in the middle of the three-element antenna array, increases by 86 MHz (from 114 MHz to 200 MHz). When the decoupling structure is loaded, the maximum gain only decreases by 0.12 dB (from 3.94 to 3.82 dB). The decoupling structure has the advantages of simple structure, easy processing, and independent design of the array, so it can be applied to multielement patch array, such as massive multiple-input multiple-output (M-MIMO) system. INDEX TERMS Linear antenna array, defect ground structure (DGS), mutual coupling, isolation.

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Abstract-Electromagnetic (EM) problem model for anisotropic plasma in kDB coordinates system is set up. And the model includes almost all the respects of EM-problems for anisotropic plasma. Based on shift-operator finite difference time-domain (SO-FDTD) method, Maxwell equations and EM-field constitutive equations are solved and discrete difference scheme of each EM-field component is obtained. Then the propagation characteristics of eigen wave are expressed by the two components of electric displacement vector as well. Lastly, three typical examples are calculated by SO-FDTD method, and the results verify the effectiveness and exactness of SO-FDTD method in kDB coordinates system.