Jia Yuan Yin

Broadband Frequency-Selective Spoof Surface Plasmon Polaritons on Ultrathin Metallic Structure

We propose an ultrathin metallic structure to produce frequency-selective spoof surface plasmon polaritons (SPPs) in the microwave and terahertz frequencies. Designed on a thin dielectric substrate, the ultrathin metallic structure is composed of two oppositely oriented single-side corrugated strips, which are coupled to two double-side corrugated strips. The structure is fed by a traditional coplanar waveguide (CPW). To make a smooth conversion between the spatial modes in CPW and SPP modes, two transition sections are also designed. We fabricate and measure the frequency-selective spoof SPP structure in microwave frequencies. The measurement results show that the reflection coefficient is less than -10 dB with the transmission loss around 1.5 dB in the selective frequency band from 7 to 10 GHz, which are in good agreements with numerical simulations. The proposed structure can be used as an SPP filter with good performance of low loss, high transmission, and wide bandwidth in the selective frequency band.

Ultra Wideband Polarization-Selective Conversions of Electromagnetic Waves by Metasurface under Large-Range Incident Angles

We propose an ultra-wideband polarization-conversion metasurface with polarization selective and incident-angle insensitive characteristics using anchor-shaped units through multiple resonances. The broadband characteristic is optimized by the genetic optimization algorithm, from which the anchor-shaped unit cell generates five resonances, resulting in expansion of the operating frequency range. Owing to the structural feature of the proposed metasurface, only x- and y-polarized incident waves can reach high-efficiency polarization conversions, realizing the polarization-selective property. The proposed metasurface is also insensitive to the angle of incident waves, which indicates a promising future in modern communication systems. We fabricate and measure the proposed metasurface, and both the simulated and measured results show ultra-wide bandwidth for the x- and y-polarized incident waves.

Capacitive-coupled Series Spoof Surface Plasmon Polaritons

A novel method to realize stopband within the operating frequency of spoof surface plasmon polaritons (SPPs) is presented. The stopband is introduced by a new kind of capacitive-coupled series spoof SPPs. Two conventional H-shaped unit cells are proposed to construct a new unit cell, and every two new unit cells are separated by a gap with certain distance, which is designed to implement capacitive coupling. The original surface impedance matching is disturbed by the capacitive coupling, leading to the stopband during the transmission of SPPs. The proposed method is verified by both numerical simulations and experiments, and the simulated and measured results have good agreements. It is shown that the proposed structure exhibits a stopband in 9–9.5 GHz while the band-pass feature maintains in 5–9 GHz and 9.5–11 GHz. In the passband, the reflection coefficient is less than −10 dB, and the transmission loss is around 3 dB; in the stopband, the reflection coefficient is −2 dB, and the transmission coefficient is less than −30 dB. The compact size, easy fabrication and good band-pass and band-stop features make the proposed structure a promising plasmonic device in SPP communication systems.

Direct Radiations of Surface Plasmon Polariton Waves by Gradient Groove Depth and Flaring Metal Structure

An efficient method to radiate surface plasmon polaritons (SPPs) directly using metallic corrugated strip with gradient grooves and flaring structure has been proposed, in which the gradient grooves are used to overcome the big mismatch of wavenumbers between SPP modes and radiated spatial waves while the flaring structure provides impedance matching in wide frequency band. Both numerical simulations and measurement results suggest good direct radiation performance of the proposed structure in a wide frequency band from 5 to 20 GHz, in which the measured radiation patterns show a high gain level of 9.9 dBi on average, and the average efficiency can achieve 92%. The proposed direct radiation structure is of great application values in communication systems and integrated circuits.

Compact Feeding Network for Array Radiations of Spoof Surface Plasmon Polaritons

We propose a splitter feeding network for array radiations of spoof surface plasmon polaritons (SPPs), which are guided by ultrathin corrugated metallic strips. Based on the coupled mode theory, SPP fields along a single waveguide in a certain frequency range can be readily coupled into two adjacent branch waveguides with the same propagation constants. We propose to load U-shaped particles anti-symmetrically at the ends of such two branch waveguides, showing a high integration degree of the feeding network. By controlling linear phase modulations produced by the U-shaped particle chain, we demonstrate theoretically and experimentally that the SPP fields based on bound modes can be efficiently radiated to far fields in broadside direction. The proposed method shows that the symmetry of electromagnetic field modes can be exploited to the SPP transmission network, providing potential solutions to compact power dividers and combiners for microwave and optical devices and systems.

An Active Wideband and Wide-Angle Electromagnetic Absorber at Microwave Frequencies

Two-dimensional (2-D) metamaterials (MTMs) can be used to create perfect electromagnetic absorbers. In this letter, a novel active MTM absorber with non-Foster loads is proposed. For obliquely incident plane waves with both transverse-electric (TE) and transverse-magnetic (TM) polarizations, its effective circuit model is analytically demonstrated, accounting the material losses. Based on the circuit model, a stability characterization is introduced to give the design principles for the non-Foster elements to achieve a wideband and wide-angle metamaterial absorber (MA). These active elements are achieved by a two-port non-Foster circuit based on the resonant tunneling diodes. For the purpose of verification, a sample active MA design is presented, exhibiting a high electromagnetic absorption rate for wideband and wide-angle incidence for both TE and TM polarizations at microwave frequencies, as compared to its passive counterpart.

Dynamic excitation of spoof surface plasmon polaritons

We propose dynamic control to excite spoof surface plasmon polaritons (SPPs) in the microwave frequency. Using switchable devices, the excitation of spoof SPPs can be turned on and off depending on the DC voltages applied on the switchable devices. To demonstrate the dynamic mechanism, a switchable spoof SPP waveguide is proposed and fabricated in the microwave frequency. Both simulation and measurement results show good performances of the dynamic control in exciting spoof SPPs.

Realization of Low Scattering for a High-Gain Fabry–Perot Antenna Using Coding Metasurface

We present a novel method to design a conventional Fabry–Perot (F-P) antenna but with low scattering. Combining a coding metasurface and an F-P antenna together could effectively reduce the scattering and keep high gain simultaneously. The coding element consists of two layers of square metallic patches printed on both sides of a dielectric substrate. The bottom metallic patch helps form a partially reflecting surface (PRS) for the F-P antenna, while the upper metallic patch is utilized to construct the coding metasurface with an optimized coding sequence, aiming to reduce the scattering of the F-P antenna by redirecting electromagnetic energies in all directions. Based on the specially designed coding metasurface, a good scattering reduction without degrading the radiation performance of the F-P antenna is achieved. Both simulated and experimental results demonstrate the excellent performance of the proposed antenna, with a peak measured gain of 19.8 dBi and a significant scattering reduction in the frequency range of 8–12 GHz.

Frequency-Controlled Broad-Angle Beam Scanning of Patch Array Fed by Spoof Surface Plasmon Polaritons

Frequency-controlled broadband and broad-angle beam scanning is proposed using a circular-patch array fed by planar spoof surface plasmon polaritons (SPPs). Here, a row of circularly metallic patches is placed near an ultrathin planar spoof SPP waveguide. When the SPP wave is transmitted through the waveguide, the circular patches are fed at the same time. Because of the phase difference fed to the patches, the proposed structure can realize wide-angle beam scanning from backward direction to forward direction as the frequency changes, breaking the limit of traditional leaky-wave antennas. Both numerical simulations and measured results demonstrate good performance of the proposed structure. It is shown that the scanning angle can reach 55° with an average gain level of 9.8 dBi. The proposed frequency scanning patch array is of great value in planar integrated communication systems.

Ultra-wideband filtering of spoof surface plasmon polaritons using deep subwavelength planar structures

Novel ultra-wideband filtering of spoof surface plasmon polaritons (SPPs) is proposed in the microwave frequency using deep subwavelength planar structures printed on thin and flexible dielectric substrate. The proposed planar SPPs waveguide is composed of two mirror-oriented metallic corrugated strips, which are further decorated with parallel-arranged slots in the main corrugated strips. This compound structure provides deep subwavelength field confinement as well as flexible parameters when employed as a plasmonic waveguide, which is potential to construct miniaturization. Using momentum and impedance matching technology, we achieve a smooth conversion between the proposed SPPs waveguide and the conventional transmission line. To verify the validity of the design, we fabricate a spoof SPPs filter, and the measured results illustrate excellent performance, in which the reflection coefficient is less than −10 dB within the −3 dB passband from 1.21 GHz to 7.21 GHz with the smallest insertion loss of 1.23 dB at 2.21 GHz, having very good agreements with numerical simulations. The ultra-wideband filter with low insertion loss and high transmission efficiency possesses great potential in modern communication systems.