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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.

In this paper, a novel compact bandpass filter (BPF) with a wide out-of-band rejection is proposed. It can achieve broadband characteristics by combining hollow bowtie-type spoof surface plasmon polaritons (SSPPs) with complementary H-type defected grounded structures (DGSs) through aperture coupling. Compared with the conventional SSPP unit cells, the hollow bowtie-type structure exhibits much better slow-wave characteristics. The introduced slant antenna type port-coupling can produce a very strong high-performance rejection outside the high frequency stopband. Simulation results show that the SSPPs-DGS-based BPF has an excellent band pass characteristics in a broadband range with − 3dB fractional bandwidth of 43.5% at center frequency f 0 of 2.04 GHz. The return loss in the passband is better than − 12 dB. Furthermore, because of the multiple transmission zeros generated in upper-stop-band, the designed BPF has an extremely strong out-of-band rejection of -40dB from 1.5 f 0 to 4 f 0 ( f 0 is the center frequency). The designed SSPPs-DGS-based BPF is fabricated by conventional printed circuit board (PCB) technology with a compact size of only 0.68λ g *0.34λ g (λ g is the wavelength at the center frequency). The measured results have a good agreement with the simulation ones, which verifies the rationality and feasibility of the design. The miniaturized wideband BPF with broad out-of-band rejection may make it has good application prospect in the new generation microwave communication field.

A compact low-profile end-fire antenna based on spoof surface plasmon polaritons (SSPPs) has been proposed. At the junction, where the antenna connects to the transmission line, there is a 180 degree balun structure for achieving end-fire radiation. Subsequently, two symmetrical transmission lines are introduced, with two parasitic patches loaded on the transmission lines for optimizing the S-parameters of the antenna. The addition of the balun structure ensures that the SSPP units operate as dipoles within the frequency band. Furthermore, the dispersion parameters of the SSPP units are simulated and analysed. The Hansen-Woodyard condition is applied to derive the maximum end-fire gain at the terminal. The results show that the end-fire antenna operates in the frequency range of 18–20 GHz, with an average gain of 10.1 dBi and a peak gain of 10.6 dBi. The proposed end-fire antenna is miniaturized and low-profile compared to conventional antennas.The simulation and measurement results are in good agreement within the operating frequency band, thus showing that the proposed design has a great potential for future wireless communication applications.

This study investigates the use of spoof surface plasmon polaritons (SSPPs) as an effective feeding mechanism for antennas functioning within the extremely high-frequency (EHF) range. A novel method is proposed for feeding a dielectric rod antenna with SSPPs, featuring a simple design made from FR-4 material with a relative permittivity of 4.3. In contrast to traditional tapered dielectric rod antennas and their feeding configurations, this design shows promise for achieving a gain of up to 16.85 dBi with an antenna length of 7.6 λ0. By carefully optimizing the design, impedance matching and directional radiation characteristics were obtained at 7.3 GHz. Simulations were conducted using CST Microwave Studio to validate and evaluate the design’s performance. The enhanced gain, improved impedance bandwidth, and use of cost-effective materials such as FR-4 present a compelling case for adopting this design in future wireless communication technologies. Additionally, the remote sensing properties of the feeder can be utilized for concealed object detection, material characterization, and the analysis of the spectral properties of materials.

Controlling energy flow in waveguides has attractive potential in integrated devices from radio frequencies to optical bands. Due to the spin-orbit coupling, the mirror symmetry will be broken, and the handedness of the near-field source will determine the direction of energy transport. Compared with well-established theories about spin-momentum locking, experimental visualization of unidirectional coupling is usually challenging due to the lack of generic chiral sources and the strict environmental requirement. In this work, we design a broadband near-field chiral source in the microwave band and discuss experimental details to visualize spin-momentum locking in three different metamaterial waveguides, including spoof surface plasmon polaritons, line waves, and valley topological insulators. The similarity of these edge waves relies on the abrupt sign change of intrinsic characteristics of two media across the interface. In addition to the development of experimental technology, the advantages and research status of interface waveguides are summarized, and perspectives on future research are presented to explore an avenue for designing controllable spin-sorting devices in the microwave band.

Quasi-line waves represent a distinct class of propagation modes along non-complementary impedance surfaces, offering an alternative to the conventional line waves typically formed by complementary impedance surfaces. In this study, we introduce a novel design for quasi-line waves utilizing non-dual, purely inductive impedance structures. By incorporating multilayer graphene, our design achieves wide bandwidth and extended propagation lengths in the terahertz range, with field concentration localized at the edges of the inductive surfaces. This configuration enables unidirectional wave propagation, with graphene integration providing precise control over bandwidth and transmission characteristics. Unlike traditional line waves, which are constrained to specific terahertz frequency ranges, our quasi-line mode—guided by self-inductive impedance surfaces—demonstrates significantly broader bandwidth and enhanced electric field intensity. The performance of this mode is strongly influenced by capacitance variations between impedance surfaces, exceeding the singularity limitation of conventional line waves. Our proposed structure demonstrates superior performance in both bandwidth and mode singularity within the terahertz spectrum, surpassing traditional line wave designs.

A novel miniaturized broadband low-pass filter (LPF) is proposed based on the integrated square dumbbell and meander (SDBM) structure spoof surface plasmon polaritons (SSPPs). Compared with the conventional H-shaped and square dumbbell structure SSPP unit-cells, the integrated SDBM structure can effectively reduce its asymptotic frequency, revealing much better slow-wave characteristics. A broadband LPF is designed by integrating two types of SDBM structure SSPP unit-cell to enhance out-of-band suppression. Finite element method (FEM) simulations demonstrate that the SDBM structure SSPPs-based LPF exhibits excellent lowpass characteristics across a broadband range of 0–2.24 GHz, achieving a remarkably high out-of-band rejection level of − 27 dB in a broadband range of 2.39–8.7 GHz. An equivalent LC circuit model is established for the proposed SDBM-structured SSPPs-based LPF, exhibiting a reasonable consistency with the FEM results. The designed LPF is skillfully realized utilizing conventional PCB manufacturing techniques, achieving with a size of only 0.238 λ c  × 0.12 λ c (λ c is the wavelength at cut-off frequency). The experimental results exhibit a remarkable consistency with the simulated data, thereby validating the soundness and practicality of the proposed design. The proposed broadband LPF featuring robust out-of-band rejection, demonstrates significant potential for integration into compact microwave and terahertz (THz) circuits, paving the way for advanced applications in these frequency bands.

A periodically corrugated metal metasurface can support spoof surface plasmon polaritons (SSPPs) at lower frequencies (e.g., terahertz (THz) and microwave ranges). In this paper, we explore a multi-bands SSPPs waveguide composed of a composite periodic metal groove (CPMG) and derive the theoretical dispersion formulas by the modal expansion method (MEM) under the deep subwavelength condition. The numerical experiments and analytical calculations are used to give a general analysis about the properties of the SSPPs on the composite periodic waveguides. It is demonstrated that the SSPPs waveguides of CPMG with multi-grooves in one period give better near-field confinement benefiting from the more electromagnetic (EM) hotspots at the surface of their periodic structure. Numerical simulations are employed to verify the theoretical analysis and demonstrate good agreement with the analytical results. The calculation methodology presented in this paper can be applied to address the miniaturization, compact design aspects of THz devices and highly sensitive trace sensing fields.

In this paper, a novel wideband antenna with a simple structure and low profile based on spoof surface plasmon polaritons (SSPPs) is proposed. The structure consists of periodically modulated corrugated metal strips as transmission lines, a CPW feed, and a ground metal plate as an antenna reflector. The SSPP transmission line is used to convert quasi-TEM to SSPP mode and achieve optimal impedance matching. The prototype of the end-fire antenna has been designed and fabricated. The simulation results show that this antenna can achieve a gain of 10.19 dB, a bandwidth of 146%, and an efficiency of 90% in a wide operating band from 7 to 45 GHz. The proposed design illustrates great potential that includes high efficiency, good directivity, high gain, wide bandwidth, and easy manufacturing.

The future wireless communications require different kinds of modulation functions to be integrated in a single intelligent device under different scenarios. Here, we propose a multi-scheme digital modulator to achieve this goal based on integrated spoof surface plasmon polaritons (SPP) in different frequency bands. By constructing switchable spoof SPP units, the propagating wave in the proposed spoof SPP waveguide can be manipulated in amplitude domain, frequency domain, and phase domain. As a proof of concept, the integrated multi-scheme digital modulator is experimentally verified to achieve at least three kinds of modulations, including amplitude shift keying, phase shift keying, and frequency shift keying, in a single digital spoof plasmonic waveguide. The simulated and measured results show that the modulator has excellent property of field confinement and is capable of frequency-domain modulation. Hence, the multi-scheme modulation property makes the proposed SPP digital modulator be an effective and reliable candidate for efficient manipulations of SPP waves and for advanced modulation technology