In this paper, a multi-band AMC-backed antenna system characterized with high gain and low-profile is proposed. It is constructed by placing a quad-band coplanar-waveguide (CPW) antenna over an AMC with four zero-phases in the reflection coefficient. The CPW antenna consists of an ornamental-pillar-shaped patch with the specially designed parasitic elements, and a defected ground structure (DGS), for the application in the frequency bands of 2.45, 3.5, 4.6 and 5.8 GHz. To improve the CPW antenna’s radiation performance, an artificial magnetic conductor (AMC) ground with four zero-phases of the reflection coefficient is designed and employed as the reflector. The AMC unit cell is composed of four metallic nested rings (FMNR), whose innermost ring is connected in series to four lumped capacitors. It is observed that the proposed quad-band AMC ground can not only increase the gains of the multi-band antenna greatly but also combine the two intermediate frequency bands of the antenna into a broadband one. The prototypes of the antenna and the AMC array with 5 × 5 unit cells were fabricated and measured. It is found that in comparison to the antenna without AMC, the AMC-backed antenna obtains a gain enhancement by amounts of 4.93, 5.92, 5.54 and 4.95 dB at the frequencies of 2.45, 3.5, 4.6 and 5.8 GHz. The 10-dB impedance bandwidths of the AMC-backed antenna include three bands of 2.13 – 2.87, 3.22 – 4.75, and 5.54 – 5.86 GHz, with the corresponding relative bandwidths of 14.8%, 38.4%, and 5.3%. The proposed antenna can be potentially applied to the applications in WLAN, WiMAX, and 5G mobile communication systems.

A miniaturized ultra-wideband (UWB) implantable antenna with hybrid polarization is proposed in this paper. The antenna has a surface size of 10×9.8 mm2, which consists of a tree-shaped radiation patch and a horseshoe-shaped defected ground structure (DGS). Because of the specially designed radiation patch and defected ground plane, the implantable antenna has realized ultra-wideband characteristics. By adding a superstrate to the antenna system, the circular polarization has been introduced to the antenna. A prototype of the antenna was fabricated and measured when it was buried inside a ground pork environment. The simulated and measured results show a fairly good agreement. A measured impedance bandwidth from 2.33 to 11.36 GHz (131%), and three wide axial ratio (AR) bandwidths of 4.4-5.2 GHz (16.67%), 6.6-8 GHz (19.18%), and 10.4-10.8 GHz (3.77%) were obtained. Furthermore, the link budget analysis and specific absorption rate (SAR) were further analyzed. It seems that the proposed antenna has a wide bandwidth, which covers the bands of the ISM, 5G, WiMAX, Wi-Fi, and satellite communication.

A hybrid framework for solving the non-uniqueness problem in the inverse design of isomorphic metasurfaces is proposed. The framework consists of a representation learning (RL) module and a variational autoencoder-particle swarm optimization (VAE-PSO) algorithm module. The RL module is used to reduce the complex high-dimensional space into a low-dimensional space with obvious features, with the purpose of eliminating the many-to-one relationship between the original design space and response space. The VAE-PSO algorithm first encodes all meta-atoms into a continuous latent space through VAE and then applies PSO to search for an optimized latent vector whose corresponding metasurface fulfills the target response. This framework gives the solution paradigm of the ideal non-uniqueness situation, simplifies the complexity of the network, improves the running speed of the PSO algorithm, and obtains the global optimal solution with 94% accuracy on the test set.

A multiband co-planar nested electromagnetically induced transparency (EIT) metamaterial based on dual modulation of vanadium dioxide (VO₂) and graphene is proposed. The single-layer structure comprises a pair of metallic T-type resonators (TRSs), a pair of VO₂-TRS with equal size, and a centrally positioned crossed graphene layer. These three layers of TRS with varying sizes undergo bight-bight coupling, enabling efficient modulation of the three-band EIT-like effect through the combination of VO₂ and graphene. Moreover, three distinct modulation mechanisms in the hybrid EIT metamaterials are revealed: 1) the number of EIT windows decreases as the surface temperature falls in the VO₂-TRS integration; 2) the centrosymmetry is broken during the I-shaped graphene integration process, allowing dynamic control of EIT switching and transmission strength under different polarization incidences; 3) redistribution of the surface electric field in the crossed graphene layer. The three EIT windows close one by one as the Fermi level increases with a maximum modulation depth (MD) of 89.4%. The designed structure achieves a maximum transmission coefficient of 0.95 and a maximum group delay of 27.6 ps in the terahertz (THz) band, indicating excellent transmission performance and slow-light characteristics. This work demonstrates the potential application of multiband THz slow-light devices and modulators.