Novel Dual-band Band-Pass Filters Based on Surface Plasmon Polariton-like Propagation Induced by Structural Dispersion of Substrate Integrated Waveguide

Holographic inspired high-performance circular polarized spoof surface plasmon polariton leaky-wave antenna excited by a novel launcher

The holographic technique is one of the simplest methods for designing antennas based on metasurface. This paper presents a spoof surface plasmon polariton (SSPP) leaky-wave antenna (LWA) based on the concept of impedance modulated metasurfaces by the anisotropic holographic technique. Instead of parasitic elements, anisotropic SSPP elements are exploited to achieve radiation with circular polarization. The characteristics of the SSPP elements are obtained by the aperture field estimate method. The hologram surface consists of hollow cross-bars unit cells. The anisotropy of each unit cell is achieved by combining the transformation optic method and the particle swarm optimization algorithm. A major challenge of the SSPP LWA based on modulated impedance surfaces is to find a suitable excitation technique. This study proposes a waveguide strip line launcher for excitation to minimize interference on the radiation pattern beam. The designed launcher provides a good impedance matching from 8 to 20 GHz, with an impedance bandwidth of 142%. The peak gain, radiation efficiency, axial ratio (AR) bandwidth, and side lobe level at the design frequency of 18 GHz are 19.7dBi, 93%, 11%, and - 12.1 dB, respectively. After optimizations and simulations are conducted using MATLAB and CST software, the proposed antenna is fabricated, and its radiation characteristics are measured. The measured results agree well with the simulated ones, indicating the high validity of the method.

Dual-band ESSPP-SSPP transmission line with independently controllable cutoff frequencies

In this work, an effective spoof surface plasmon polariton (ESSPP)-SSPP transmission line (TL) is proposed, which can operate in dual bands. Unlike SSPP TL, our ESSPP-SSPP TL allows for relatively accurate parameter estimation, independent control over each cutoff frequency, and low insertion loss. We provided the dispersion relation and closed-form formulas for calculating each cutoff frequency and explained the mechanism behind the independent controllability of each cutoff frequency. This allows us to quickly estimate the structural parameters with an analytical design approach. By leveraging the dispersion of the ESSPP-SSPP mode, we designed a dual-band filter operating in the millimeter-wave range, and its performance was validated through experimental measurements. This work paves the way for the development of novel SPP-like microwave/millimeter-wave devices.

Terahertz dual-band bandpass filter based on spoof surface plasmon polaritons with wide upper stopband suppression

In this paper, a terahertz (THz) dual-band bandpass filter based on spoof surface plasmon polaritons (SSPPs) with wide upper stopband suppression is proposed. The filter utilizes two types of SSPP unit cells loaded on a double-sided quasi-SSPPs transmission line to achieve dual-band filtering responses and wide upper stopband suppression simultaneously. The performance and bandwidth of the filter's passbands can be adjusted by modifying the SSPP unit cells within the dual-band filtering part. The detailed design method is provided to enhance understanding of the operating principle of the presented filter. The simulation results of the designed THz filter demonstrate its excellent dual-band filtering performance. It features a wide stopband spanning from 0.91 to 1.45 THz with |S21| < -35 dB. To validate the proposed approach, a microwave filter with a similar design is implemented. Finally, the simulated and measured S-parameter responses of the filter are provided for comparison and evaluation.

Dispersion curve engineering for automated topology design of a unit cell in spoof surface plasmon polaritons

In this paper, an automatic design method is proposed for unit cell in spoof surface plasmon polaritons (SSPP) with an almost arbitrary dispersion curve. In this method, the pixel configuration is considered for the unit cell and, by using the binary particle swarm optimization method, the proper topology of the unit cell is explored so as to reach the target dispersion curve. Unlike the traditional method of controlling the dispersion curve, which is performed based on changing the geometric parameters of the predetermined unit cell, in this method, there is no need to know the shape of the unit cell, and the dispersion curve of the modes of SSPP unit cell can be controlled independently with more freedom. Two unit cell samples are designed in order to show the efficiency of the procedure. In the first sample, the dispersion curve is designed to have the lowest asymptotic frequency; in the second sample, the dispersion curve of the second mode is controlled independently from the first mode and is changed arbitrarily. SSPP transmission lines which are related to the unit cells of the two samples are designed, and it is demonstrated that measurement and simulation results are greatly in line with each other.

Stepped waveguide metamaterials as low-loss effective replica of surface plasmon polaritons

Surface plasmon polaritons (SPPs) have attracted intensive attention for the unprecedented developments of light-matter interactions in optics and photonics, providing a feasible method for light confinement and transmission at a subwavelength scale. However, SPPs traditionally suffer from large losses due to the intrinsic dissipations and absorptions, which hinder further development and applications of SPPs. Here, we theoretically and experimentally investigate the concept of stepped waveguide metamaterials behaving as low-loss effective replicas of SPPs. The proposed structure without natural plasmonic material maintains the identical field configuration to that in regular SPP but avoids the inherent losses, outperforming regular low-loss SPP design with natural plasmonic materials on SPP propagation lengths. Furthermore, stepped waveguide metamaterial exhibits excellent compatibility in direct interconnections with arbitrary regular SPP and potentially represents a feasible route toward new SPP devices with low-loss advantages.

Waveguide effective plasmonics with structure dispersion

Plasmonic phenomena on the surface between metal and dielectric have received extensive attention, and have boosted a series of exciting techniques. Plasmonics describes the interaction between light and electronics and shows great potential in nanophotonics, optoelectronic devices, quantum physics, and surface-enhanced spectroscopy, etc. However, plasmonic phenomena are always suffering from the inherent loss issue of plasmonic materials at optical frequency, which has restricted further applications of plasmonics. In this review, we focus on the technique of waveguide effective plasmonics, which is a feasible low-loss realization of plasmonic metamaterials in lower frequency based on the structural dispersion. This review provides the underlying physics of the waveguide effective plasmonics and its applications varying from classical plasmonic concepts to novel effective plasmonic devices. Finally, we make a brief discussion on the direction of future researches and a prospect of the potential applications.

A Spoof Surface Plasmon Polaritons (SSPPs) Based Dual-Band-Rejection Filter with Wide Rejection Bandwidth

This paper presents a novel single-layer dual band-rejection-filter based on Spoof Surface Plasmon Polaritons (SSPPs). The filter consists of an SSPP-based transmission line, as well as six coupled circular ring resonators (CCRRs) etched among ground planes of the center corrugated strip. These resonators are excited by electric-field of the SSPP structure. The added ground on both sides of the strip yields tighter electromagnetic fields and improves the filter performance at lower frequencies. By removing flaring ground in comparison to prevalent SSPP-based constructions, the total size of the filter is significantly decreased, and mode conversion efficiency at the transition from co-planar waveguide (CPW) to the SSPP line is increased. The proposed filter possesses tunable rejection bandwidth, wide stop bands, and a variety of different parameters to adjust the forbidden bands and the filter’s cut-off frequency. To demonstrate the filter tunability, the effect of different elements like number (n), width (WR), radius (RR) of CCRRs, and their distance to the SSPP line (yR) are surveyed. Two forbidden bands, located in the X and K bands, are 8.6–11.2 GHz and 20–21.8 GHz. As the proof-of-concept, the proposed filter was fabricated, and a good agreement between the simulation and experiment results was achieved.