This paper proposes a dual-band eight-antenna array for multiple input and multiple output (MIMO) applications in 5G mobile terminals. The designed MIMO antenna array comprises eight L-shaped slot antennas based on stepped impedance resonators (SIRs). The required dual-resonance can be obtained by adjusting the impedance ratio of the SIR, and good impedance matching can be ensured for each antenna element by tuning the position of the microstrip feed line. The experimental results show that a measured return loss of higher than 10 dB and a measured inter-element isolation of greater than 11.2 dB have been obtained for each antenna element with a simulated total efficiency of larger than 51% across the long term evolution (LTE) band 42 (3400–3600 MHz) and LTE band 46 (5150–5925 MHz). In addition, the measured envelope correlation coefficient (ECC) is lower than 0.1 between arbitrary two antenna elements and the proposed MIMO antenna array realizes a simulated channel capacity of higher than 36.9 bps/Hz within both operation bands. Furthermore, the MIMO antenna array can maintain acceptable radiation and MIMO performance in the presence of specific anthropomorphic mannequin (SAM) head and human hands.

A class of millimeter-wave E-plane waveguide bandpass filters (BPFs) based on spoof surface plasmon polaritons (SSPPs) have been presented in this article. Three kinds of SSPPs, with different patterns coated on the dielectric substrate, are inserted into the E-plane of WR-10 standard rectangular waveguide for the design of BPFs. To clarify the filtering characteristics of the proposed BPFs, the dispersive properties of different SSPP unit cells are investigated and discussed. The electromagnetic simulation results demonstrate that the bandwidths and center frequencies of the proposed E-plane waveguide BPFs can be flexibly adjusted by controlling the asymptotic frequencies of SSPP unit cells. For verifying the design feasibility, these three E-plane waveguide BPFs are fabricated and measured. Good agreement between measurements and simulations indicates that the proposed idea will be a good candidate for the BPF design with low insertion loss and flexible adjustment of center frequency and bandwidth.

In this paper, a dual circularly-polarized (CP) multi-beam antenna is proposed for future vehicular radar applications. The antenna is composed of two pillbox reflector beamforming networks (BFNs) and a series-fed microstrip line based dual CP leaky-wave antenna (LWA) array, which has a symmetrical structure and can obtain both left hand circular polarization (LHCP) and right hand circular polarization (RHCP) by switching the exciting current direction of the microstrip line. Besides, a shorted stub is loaded in the LWA to suppress the open-stop band (OSB), and thus achieve the broadside radiation and good impedance matching of the LWA. To realize the dual-polarized radiation characteristic with low-cost passive beam scanning capability, two pillbox BFNs are connected at both sides of the LWA to share the LWA aperture. The two different BFNs can excite different CP radiation patterns. A prototype of the proposed antenna is fabricated in the frequency band 23.5–24.5 GHz, and the measured results approve that the proposed antenna can realize ±36° beam scanning range with −4.0 dB crossover level, and the gain is higher than 17.7 dBi in the operating band. The advantages of the proposed antenna, including low-profile, low-cost, passive beam scanning ability, and dual circular polarization, make it an attractive choice for low-cost millimeter-wave radar applications.

In this letter, an active metasurface for vortex beam generation is proposed. This metasurface can transform the incident plane wave into beams carrying orbital angular momentum (OAM) of three different orders. This active metasurface is composed of an array of varactor diodes loaded unit cells. The transmission phase of each metasurface unit cell can be fully controlled by the capacitance of the varactor diodes. Different modes of vortex beams can be separately generated by simply changing the transmission phase distribution on the metasurface aperture. The properties of the proposed active metasurface are demonstrated by simulation and measurement results, which have a good agreement with each other.

A hybrid implicit explicit-finite-difference time-domain (HIE-FDTD) method is used to simulate a graphene-based absorber. Both the interband conductivity and intraband conductivity of the graphene are incorporated into the HIE-FDTD method directly through an auxiliary difference equation. Because the time step size in the proposed method is not confined by the fine spatial cells in the graphene layer, the simulation time of the proposed method is greatly reduced compared with that of the conventional FDTD method. By using the proposed HIE-FDTD method, a graphene-based absorber is simulated and analyzed. The numerical result shows that the operating frequency of the absorber is tunable through controlling graphene's chemical potential. It also shows that the interband conductivity has an important effect on the performance of the graphene device, especially at the frequency band larger than 10 THz.

This paper proposes a new design of dual-band reactively loaded annular slot antenna (ASA) for dual-sense circular polarization radiation. Two concentric annular slots excited by a common microstrip feedline are employed to realize dual-band operation. Each slot can radiate a circularly polarized (CP) wave with a specified sense at its one or one-and-a-half wavelength resonance, given that an appropriately valued reactive component, i.e. capacitor or inductor, is introduced at a pre-determined location. A small frequency ratio (FR) can be achieved between the two oppositely-sensed CP bands when a capacitor and an inductor are loaded, respectively, onto the inner and outer annular slots. Contrarily, two oppositely-sensed CP bands that possess a large FR can be yielded when an inductor and a capacitor are loaded onto the inner and outer annular slots, respectively. For experimental verification, two antenna prototypes with FRs of 1.63 and 2.41 have been designed, fabricated, and measured. The measurement results exhibit a good agreement with the simulation ones. Details of design concerns and experimental results are presented and discussed.