Spoof Surface Plasmonic Waveguide Research Articles

Terahertz dual-beam leaky-wave antenna based on composite spoof surface plasmon waveguide

Terahertz dual-beam leaky-wave antenna based on composite spoof surface plasmon waveguide

A novel dual-beam terahertz leaky-wave antenna based on spoof surface plasmon waveguide

A novel dual-beam terahertz leaky-wave antenna based on spoof surface plasmon waveguide

Independently controllable dual band filtering characteristics of a spoof surface plasmonic waveguide employing compound slot structure

The dual band filtering characteristics of a spoof surface plasmonic waveguide (WG) loaded with a composite slot structure are studied in the present paper. The proposed composite slot structure enables the plasmonic WG to work at dual bands in the microwave region, where the working bandwidth can be flexibly adjusted with a broad isolation band between them. In particular, the second bandwidth can be adjusted independently without affecting the first passband by controlling the special parameter of the composite slot. As a demonstration, the measurement results of the proposed prototype filter illustrate that the plasmonic filtering WG has a dual bandpass performance with excellent frequency selectivity, where the insertion loss of the dual-band filter is less than −3 dB in the frequency from 2.7 GHz to 6.7 GHz and 7.7 GHz to 9.1 GHz, and the stopband rejection level is lower than −10 dB from 6.9 GHz to 7.5 GHz. Compared with the traditional dual band plasmonic filtering WG, the proposed filter has compact physical size, lower insertion loss in the passband and stronger isolation ability between the two passbands.

Compact spoof surface plasmonic waveguide with controllable cutoff frequency and wide stop band

To adjust the transmission band while keeping the width of a spoof surface plasmon polariton (SSPP) waveguide unchanged, periodic cells with T-shaped conductor branches on both sides are used. By controlling the top lateral strips of branches, the adjustable range of cutoff frequencies can reach approximately 3.5 GHz. Thus, compromised regulation of the field confinement and transmission loss is easily achieved, improving the transmission performance of SSPP modes. By loading open conductor rings onto T-shaped branches to construct a split ring resonator (SRR), a band-rejection filter is realized. When multiple SRRs with gradient lengths are loaded onto one side of the SSPP waveguide, a broad stop band with a relative bandwidth of 18% is achieved. The proposed structures are also advantageous for the miniaturization of microwave circuits.

Spoof surface plasmon analysis based on Marcatili’s method

Motivated by surface plasmon polariton waveguides in the optical regime, spoof surface plasmon (SSP) waveguides have received a lot of attention in terahertz and millimeter wave frequencies. Most research on these kinds of waveguides is numerical. However, some limited analytical work can be seen in the literature. In this paper, one type of SSP waveguide that is composed of a rectangular corrugation with finite lateral width on the ground is considered, and an analytical method, which is inspired by Marcatili’s method, is proposed in order to calculate the dispersion curve of the first mode. The results of this analytical method and a numerical commercial eigenmode solver are compared. The accuracy of this method by varying different geometrical parameters is shown. Finally, it is shown that this method works well in predicting the electromagnetic fields of the first mode.

Broadband bandpass filter with double‐layered spoof surface plasmon waveguide as main transmission line

In this article, double-layered spoof surface plasmon waveguide (DLSSPW) which consists of double-layered metal gratings is used as a main transmission line for realizing a broadband bandpass filter with a center frequency of 1.5GHz and a relative bandwidth of 80%. Four equally spaced short-circuited double-stripped lines are used as resonators and mounted on the main transmission line. Efficient conversion from the quasi-transverse electromagnetic (TEM) waves in the coplanar waveguide to spoof surface plasmon polaritons (SSPPs) in the DLSSPW is achieved by using gradient double-layered metal gratings and sector-structure impedance matching circuit. This filter has lower insertion loss than using single-layered spoof surface plasmon polaritons, as the DLSSPW has tighter field confinement and lower radiation loss. Moreover, due to the slow-wave effect of DLSSPW, the main-part length of the filter is shorter than microstrip-form counterpart by 30%. The measured S-parameters of the plasmonic bandpass filter agree well with the simulated ones, validating the good features.

Spatial Multi-Polarized Leaky-Wave Antenna Based on Spoof Surface Plasmon Polaritons

A leaky-wave antenna (LWA) is proposed on the basis of an ultrathin spoof surface plasmonic (SSP) waveguide, which can convert SSP waves into spatial multi-polarized radiation waves. The SSP waveguide is composed of a metallic strip line with periodic unit cells, and each unit consists of two orthogonally beveled slots. The feature of the single-conductor SSP waveguide determines that the leaky-wave radiation pattern is omnidirectional in the azimuth direction around LWA. Due to the design of orthogonally beveled slots, different polarized radiations can be achieved along the azimuth direction. Simulation results show that left-handed circularly polarized (LHCP), right-handed circularly polarized (RHCP), and linearly polarized (LP) radiations are achieved in different azimuth directions simultaneously, which are further validated by the experimental measurement. We also demonstrate a purely single polarized radiation by placing a metal reflector close to LWA, and the polarization is reconfigurable among LHCP, RHCP, and LP by mechanically rotating LWA.

A spoof surface plasmon leaky‐wave antenna with circular polarization

In this article a circularly polarized (CP) leaky-wave antenna (LWA) based on spoof surface plasmon (SSP) is proposed. Corrugated circular patches are loaded on either side of the SSP waveguide periodically and asymmetrically, which enables continuous CP beam steering from backward to forward quadrant eliminating “the open stopband” at broadside. The antenna exhibits an impedance bandwidth of 43.5% (<−10 dB) and a 3-dB axial-ratio bandwidth of 27.8%; within the impedance bandwidth from 4.5 to 7 GHz the radiation beam can be steered from 120° to 70°. With a ground plane placed underneath, the antenna can achieve average radiation gain and efficiency of about 10 dBic and 84.2%, respectively, showing a radiation gain increase of about 3 dB over that without a ground plane. The proposed SSP-based CP LWA is expected to find applications in wireless communication systems based on planar antennas.

Controllable Filtering Structure Using Magnetic Coupling Between Spoof Plasmonic Waveguide and Solid Dielectric Resonators

The structure and electrical characteristics of a dielectric resonator (abbreviated as DR hereafter) loaded plasmonic waveguide with controllable bandwidth are investigated in the present research. By loading the high permittivity dielectric medium on a spoof surface plasmonic waveguide, the working bandwidth of the filtering structure can be regulated flexibly due to the resonant effect of the loaded cylindrical DR. The DR is home-made and possesses the permittivity of 25.66, tanδ of 5.3 × 10 -5 and stable temperature coefficient of -6.3 ppm/°C in microwave region. After the DR is loaded, the filtering structure can form the transmission zero on the edge of the pass band, regulating the bandwidth as well as increasing the out-of-band rejection. By controlling the height between the loaded DR and the substrate, or adjusting the inter-distance between the DRs, the relative bandwidth of the filtering structure can be effectively tailored.

Spoof surface plasmonic waveguide and its band-rejection filter based on H-shaped slot units

To reduce the transverse width of the SSPP (spoof surface plasmon polaritons) waveguide, the complementary structure of the SSPP waveguide based on the H-shaped conductor periodic unit is used. In this structure, periodic H-shaped slots are cut in the conductor film on the substrate interface. Fed by the coplanar waveguide with flared ground planes, this SSPP waveguide with a small width can achieve broadband transmission characteristics below 10 GHz. Inserting small H-shaped conductor units inside the slot can form the complementary split ring resonators, and the band-stop filter is realized without increasing the lateral dimension of the original SSPP waveguide. The experimental results show that the notch frequency of the proposed filter can be effectively regulated by the height of embedded H-shaped conductor units.

A planar strongly confined spoof surface plasmonic waveguide with compact cells

ABSTRACTA new planar waveguide structure, based on spoof surface plasmon polaritons (SSPPs), is proposed featuring compact size, low loss, and good subwavelength field confinement. Compared with the rectangular- and trapezoidal-type cells in the conventional spoof surface plasmonic waveguides (SSPWs), the proposed cell has 50.7% and 27.8% size reduction at the same cut-off frequency, respectively. Moreover, the simulated electrical field distributions show that there are good improvements in the field enhancement and subwavelength confinement. To further validate the transmission characteristics of the proposed waveguide, coplanar waveguide (CPW) and corresponding transition structures are used to get a high efficient mode conversion. A CPW-SSPW-CPW structure on a dielectric board is designed, fabricated, and measured in the microwave region. Good agreement is achieved between the simulated and measured results. The last results show that the proposed waveguide has low insertion loss and flat group delay in an ultra-wideband from 2.4 to 10.3 GHz.

Flexibly designed spoof surface plasmon waveguide array for topological zero-mode realization.

We propose a flexibly designed photonic system based on ultrathin corrugated metallic "H-bar" waveguide that supports spoof surface plasmon polariton (SPP) at microwave frequencies. Five designs were presented, in order to demonstrate flexibility according to varying height, period, core width, rotation, and shifting on the "H-bar" unit of the waveguide. The propagation constant between two hybrid designs of period and height structure was then shown in order to study the coupling effect. Next, we constructed a coupled waveguide array that followed the Su-Schrieffer-Heeger (SSH) model. This model was constructed by a hybrid design with the identical propagation constant of each waveguide, except it had dimerized spacing. The propagation feature of topological zero mode was then observed as theoretically expected in the dimerized array. Our proposed spoof SPP waveguide array has great flexibility to be used as a powerful experiment platform, particularly in photonic simulation of the quantum or topological phenomena described by Schrödinger equation in condensed matters.

Spoof surface plasmonic waveguide devices with compact length and low-loss

A spoof surface plasmon polaritons (SSPPs) waveguide structure with periodic T-grooves is proposed and investigated in this paper. Compared to the conventional plasmonic waveguide with periodic rectangular-grooves, the proposed waveguide support the guided SSPPs wave with enhanced propagation confinement. Moreover, the waveguide with T-grooves can achieve 39.4% decrease in length compared with the rectangular-grooves waveguide. The propagation properties of the SSPPs with enhanced confinement are able to improve by adjusting the shape dimensions of T-grooves. The effects of bend radius of 90° T-grooves waveguide on propagation performance are analyzed, and the good transmission characteristics of waveguides with small bend radius are verified. The experimental verifications of the T-grooves plasmonic waveguide filter and 3 dB power divider in microwave region are realized, S21-parameter of waveguide filter is very close to 0 dB from 0 GHz to 5.6 GHz. And 3 dB power divider achieves very good power equipartition from 0 GHz to 5.5 GHz.

2D circularly polarized antenna array fed by spoof surface plasmonic waveguide

A two-dimensional high-gain circularly polarized (CP) patch array antenna operating in Ku band is proposed in this article. To excite a novel spoof surface plasmonic transmission line (SSP-TL), which is mounted vertically on the ground, a waveguide with a transition are used for the momentum and impedance matching. A SSP-TL 4-way power divider is then used to feed a 4 × 7 circular patch array by travelling waves. Therefore, the CP radiation is generated on the patches located between the parallel SSP-TLs. Avoiding the deterioration in axial ratio, 90° phase difference between adjacent SSP-TLs is designed by tuning the height of the SSP-TLs, as the dispersion property is influenced by the height of the corrugations obviously. The simulated maximum gain of 20.6 dBi is achieved at 15.2 GHz, together with the axial ratio of 0.8 dB. A prototype is fabricated and measured to validate the proposed antenna array.

Ultra-Low-Loss High-Contrast Gratings Based Spoof Surface Plasmonic Waveguide

Large metallic losses and short propagation lengths associated with surface plasmons (SPs) have long been considered as the obstacles which severely limit the practical applications of surface plasmonic waveguides. In this paper, we introduce the concept of dielectric spoof SPs (SSPs) and show that subwavelength high-contrast gratings (HCGs) offer a route to effectively suppress the losses and hence dramatically increase the propagation length of surface electromagnetic waves. We experimentally realized a wideband ultra-low-loss high-confinement plasmonic waveguide constructed by a high refractive-index dielectric array with deep-subwavelength periodicity on a metal substrate. Simulation and measurement results on the near-field distributions and S-parameters at microwave frequencies provide explicit evidences of strong field localization and show excellent transmission efficiency of HCGs-based SSPs across a broad frequency band. More importantly, the propagation length of the HCGs-based SSPs is proved to be at least more than one order of magnitude larger than that of metallic gratings-based SSPs at the same or even higher level of field confinement. Thus, the SSPs as experimentally realized in this paper hold great promise for numerous practical applications in ultra-low-loss and long-range transmission SP devices and circuits and may open up new vistas in SP optics.

Diffraction radiation based on an anti-symmetry structure of spoof surface-plasmon waveguide

Spoof surface-plasmon (SP) modes can be excited efficiently and propagate along the surface of double-layer corrugated metallic strips with anti-symmetry. Here, we propose a spoof SP structure with diffraction radiation, which is achieved by introducing phase-reversal geometry into the SP waveguide structure with a π-phase shift for adjacently reversed units. At the junction between two adjacent units, the discontinuity of the periodic structure can be viewed as a perturbation to generate space harmonics, thereby enabling efficient conversion of SP modes into free-space radiation modes. We demonstrate experimentally that the resultant radiation is analogous to Cherenkov radiation wakes, which occurs in the form of a radiation cone. The vast majority of the energy based on the surface wave is emitted into the free space. We expect that the proposed method could be an alternative to transforming the spoof SP modes into the radiation modes.

Enhanced terahertz sensing with a coupled comb-shaped spoof surface plasmon waveguide.

A comb-shaped waveguide based on the excitation of coupled spoof surface plasmon (CSSP) mode is investigated, and is found to have a pronounced effect for the enhancement of fingerprint detection sensitivity in the terahertz (THz) regime. Composed of two oppositely oriented metal stripes with single-side comb-shaped corrugations, the waveguide is formed due to the coupling of SSP modes supported by metal corrugations on both sides and the mode is tightly localized between the central gap, which provides a perfect site for accommodating the samples in THz sensing. The effective detection of thin-layer lactose is given as an example to demonstrate the sensitive detection of it at a thickness of only a few microns. A transmission spectrum through the waveguide with a pronounced dip at its characteristic absorption frequency of 0.529THz is shown, which can never be observed using the transmission through a lactose layer with the same thickness.

Broadband transition between microstrip line and spoof SP waveguide

A broadband transition from microstrip line to spoof surface plasmon (SP) waveguide is proposed. The transition transforms the guided wave into a spoof SP polariton in a broad microwave frequency band. A back-to-back transition sample is fabricated using the proposed method. Good agreement between the measurement and simulation is obtained. The measured results show an insertion loss <2 dB and a return loss below −11 dB from 2.2 to 10 GHz. The proposed broadband transition may pave a way for advanced conventional plasmonic integrated microwave devices and circuits.

Feasibility of spoof surface plasmon waveguide enabled ultrathin room temperature THz GaN quantum cascade laser

AbstractWe propose and study the feasibility of a THz GaN/AlGaN quantum cascade laser (QCL) consisting of only five periods with confinement provided by a spoof surface plasmon (SSP) waveguide for room temperature operation. The QCL design takes advantages of the large optical phonon energy and the ultrafast phonon scattering in GaN that allow for engineering favorable laser state lifetimes, and the SSP waveguide provides the optical confinement for the ultrathin QCL. Our analysis has shown that the waveguide loss is sufficiently low for the QCL to reach its threshold at the injection current density around 6 kA/cm2 at room temperature.

Defining Material Parameters in Commercial EM Solvers for Arbitrary Metal-Based THz Structures

Frequency-domain solvers are used extensively for modeling arbitrary metal-based terahertz structures. Four well-known commercially available electromagnetic (EM) modeling software packages include HFSS™, CST Microwave Studio®, EMPro, and RSoft. However, there are a number of operational issues that relate to how they can be used to obtain more meaningful and accurate results. Even experienced users of these and similar software packages may not fully appreciate some of the subtle ambiguities in defining boundaries and material parameters for use in THz applications. To this end, a detailed comparative study has been undertaken, in consultation with all four vendors. First, in order to avoid introducing ambiguities, frequency dispersion in materials has to be clearly defined from first principles; in both intrinsic and effective forms. Different frequency dispersion models are then introduced for `metal-like' materials. To act as benchmark structures, conventional air-filled metal-pipe rectangular waveguides, associated cavity resonators and a spoof surface plasmon waveguide have been simulated, using a raft of different approaches; with a view to illustrating quantifiable weaknesses in commercial software packages for simulating arbitrary metal-based THz structures. This paper highlights intuitive and logical approaches that give incorrect results and, where possible, makes recommendations for the most appropriate solutions that have hitherto not been given in Technical Notes.