In this article, propagation loss is investigated for a surface wave (SW) when enters from a scalar impedance surface (SIS) to a tensor impedance surface (TIS). This loss has two components: (a) loss due
In this article, propagation loss is investigated for a surface wave (SW) when enters from a scalar impedance surface (SIS) to a tensor impedance surface (TIS). This loss has two components: (a) loss due to change in the propagation direction and mode transformation of the SW and (b) loss due to the surface impedance mismatch between the SIS and the TIS. First, two analytical methods are presented to calculate the loss and then the methods are verified by a sample structure, which is fabricated with the printed circuit technology at 15.1‐15.75?GHz frequency bandwidth. The calculated total loss for the sample structure is 8.7?dB and 5.6?dB at 15.1 and 15.7?GHz, respectively, which is in good agreement with the measured results.
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This paper develops a framework for designing wideband reflectarray antennas. The proposed reflectarray is implemented as a scalar impedance surface composed of subwavelength elements, whose response is designed to realize a Besse...
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This paper develops a framework for designing wideband reflectarray antennas. The proposed reflectarray is implemented as a scalar impedance surface composed of subwavelength elements, whose response is designed to realize a Bessel filter response. The underlying unit cells therefore have maximum group delay bandwidth with no group delay ripples in the passband. It is shown that the reflectarrays designed using this Bessel filter approach exhibit wide bandwidth only limited by the order of the filter used to realize the Bessel filter. Simulated and measured antenna characteristics of the proposed reflectarray are presented for a C-/X-band reflectarray design. It is shown to have good beam characteristics and ultra-low temporal dispersion from 5 to 10 GHz, two attractive qualities accomplished simultaneously by the proposed reflectarray.
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An electronically controllable microstrip leaky-wave antenna (LWA) to steer the radiations at a fixed frequency is presented. The proposed LWA is composed of a corrugated microstrip line loaded by the varactor diodes with triangul...
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An electronically controllable microstrip leaky-wave antenna (LWA) to steer the radiations at a fixed frequency is presented. The proposed LWA is composed of a corrugated microstrip line loaded by the varactor diodes with triangular-modulated surface impedance. Due to the periodical modulation of the surface impedance, the guided waves can be converted into the leaky-wave radiations efficiently with frequency-scanning property. Furthermore, the surface impedance of the LWA can be reconfigured by changing the capacitance of the varactor diode through dc bias voltage, which will make the radiation beam steer in a large angle range accordingly at a fixed frequency. Both numerical simulations and experimental results show that the radiation beams can be controlled for continuously steering at each frequency from 5.5 to 5.8 GHz by changing the dc bias voltage from 0 to 20 V, in which the scanning angle can reach as high as 45°.
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The surface impedance and dispersion equation of a printed-circuit tensor impedance surface (PCTIS) are derived using a modified transverse resonance technique. A PCTIS consists of a subwavelength-patterned metallic cladding over ...
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The surface impedance and dispersion equation of a printed-circuit tensor impedance surface (PCTIS) are derived using a modified transverse resonance technique. A PCTIS consists of a subwavelength-patterned metallic cladding over a grounded dielectric substrate. The metallic cladding is analytically modeled as a tensor impedance sheet. An explicit expression is derived for the effective surface impedance of the PCTIS using a transmission-line approach. First, the surface-impedance expression is found for a printed-circuit scalar impedance surface using the transverse resonance technique. Next, a modified transverse resonance technique is applied to an idealized tensor impedance boundary condition (TIBC) to find its dispersion equation. Finally, the analysis of the printed-circuit scalar impedance is combined with that of the idealized TIBC to find the tensor surface impedance and dispersion equation of a PCTIS. A discussion of the principal axes and the propagation of TM and TE waves is provided. The special case of electrically thin PCTISs is also analyzed and discussed.
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A synthesis method for printed-circuit tensor impedance surfaces (PCTISs) is presented that allows arbitrary control of phase progression and power flow of guided waves. PCTISs consist of a subwavelength-patterned metallic claddin...
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A synthesis method for printed-circuit tensor impedance surfaces (PCTISs) is presented that allows arbitrary control of phase progression and power flow of guided waves. PCTISs consist of a subwavelength-patterned metallic cladding atop a grounded dielectric substrate. The cladding is modeled by an anisotropic tensor sheet admittance. The synthesis method employs field analysis to determine the required tensor sheet admittance values for a prescribed phase progression and power-flow direction. An inhomogeneous distribution of PCTIS unit cells can be used to design a 2-D metasurface capable of spatial control of surface waves. A collimator is designed to verify the proposed synthesis procedure and demonstrate its utility.
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Electrically triggered vacuum surface flashover switches (VSFSs) offer the advantages of rapid closure, high-pulsed repetition frequency, high reliability, and compact design for high pulse power technology. The output performance...
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Electrically triggered vacuum surface flashover switches (VSFSs) offer the advantages of rapid closure, high-pulsed repetition frequency, high reliability, and compact design for high pulse power technology. The output performance of the pulsed power system, as well as the lifetime of VSFS, is limited by the plasma impedance during the VSFS turn-on process. This article presents a theoretical calculation of the plasma impedance based on experimental measurements and second-order Taylor series, and the mathematical expressions of plasma impedance and ohmic loss are performed. From the experimental waveform and the theoretical calculation of the expression, the variation curve of the plasma impedance is derived. Finally, the influencing factors (operating voltage, loop resistor, discharge capacitor, trigger resistor, and trigger voltage) are investigated. The experimental results indicate that an increase in operating voltage can increase the plasma resistance drop rate and can reduce the plasma ohmic loss. The same trend is also achieved by decreasing the loop resistor. Moreover, the discharge capacitance, trigger voltage, and trigger current only affect the ON-state stage and the trigger process, and the impact on the plasma resistance and ohmic loss during the closing process is weak.
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Metasurfaces composed of subwavelength unit cells usually require a large number of unit cells which lead to complicated design and optimization. Aggressive discretization in metasurface designs can significantly reduce the number...
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Metasurfaces composed of subwavelength unit cells usually require a large number of unit cells which lead to complicated design and optimization. Aggressive discretization in metasurface designs can significantly reduce the number of unit cells within a period, resulting in large unit cell sizes. The enlarged unit cells will encounter negligible mutual couplings when combined together, hence making straightforward the process of metasurface design. These advantages combine to allow the design of a novel class of metasurfaces which support the high efficiency redirection of electromagnetic (EM) waves over a wide bandwidth and operation angle. Moreover, an aggressively discretized metasurface can realize diffraction mode circulation. In this work, we propose a simple transmissive metasurface which can realize diffraction mode circulation by refracting plane waves from angles of $\mathrm {-45^{\circ }}$ , $\mathrm {0^{\circ }}$ , and $\mathrm {45^{\circ }}$ to angles of $\mathrm {0^{\circ }}$ , $\mathrm {45^{\circ }}$ , and $\mathrm {-45^{\circ }}$ , respectively. The power efficiency of each anomalous refraction is more than 80% at the design frequency of 28 GHz, and the 3 dB power efficiency bandwidth is 11%. We fabricated and measured the metasurface, the experiment results agree well with the simulation results.
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Using anisotropic holographic metasurfaces to transform the creeping waves into circularly polarized (CP) beams has initiated the quest for tangible applications in different disciplines. However, the present designs are only limi...
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Using anisotropic holographic metasurfaces to transform the creeping waves into circularly polarized (CP) beams has initiated the quest for tangible applications in different disciplines. However, the present designs are only limited to the planar impedance surfaces with rare studies concerning the linear-to-circular polarization converting holographic metasurface over the conformal platforms. In this article, we demonstrate the perfect transformation of linearly polarized (LP) surface waves into CP waves through cylindrical anisotropic holographic metasurfaces consisting of gradient H-shaped slits etched on the periodic circular patches. Especially, the linear-to-circular polarization conversion rate can always maintain a very high level for the beam synthesis no matter how the curvature of the metasurface changes, and such high-purity CP beams also demonstrate very good quality of steerable characteristics over conformal surfaces. Our approach, using anisotropic holographic metasurfaces to transform the creeping waves into high-purity CP beams, should pave the way for more advanced functional meta-device designs over the nonplanar impedance surfaces.
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In this work, we investigate the far-infrared wave properties for a ferroelectric material, i.e., lithium tantalate (LiTaO3), in the double-negative region, i.e., both the real parts of permittivity and permeability are negative. ...
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In this work, we investigate the far-infrared wave properties for a ferroelectric material, i.e., lithium tantalate (LiTaO3), in the double-negative region, i.e., both the real parts of permittivity and permeability are negative. The analysis has been done based on the calculated surface impedances for three model structures, i.e., material occupying semi-infinite space (structure I), material of a slab immersed in free space (structure II), and a layered structure made of film on a dielectric substrate (structure III). It is found that the surface impedance spectrum exhibits resonant behavior. In structure I, there are only two resonant points, which arise mainly from the pole of permeability and the zero of permittivity. In structure II, multiple resonances can be found, and they strongly rely on the film thickness. Finally, we specifically investigate the substrate resonant phenomenon in structure III.
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Surface waves are demonstrated theoretically to propagate along periodically corrugated surfaces made of non-conductive lossless materials with positive permittivity. An analytic derivation of the surface wave dispersion relation ...
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Surface waves are demonstrated theoretically to propagate along periodically corrugated surfaces made of non-conductive lossless materials with positive permittivity. An analytic derivation of the surface wave dispersion relation is presented in the case of the deeply subwavelength period of a corrugated structure using impedance boundary conditions (IBCs) at the interfaces. Thus obtained dispersion relation is verified numerically and limitations as well as the physicality of IBCs when modeling surface waves are discussed. Finally, suitable materials, potential experimental realization, and sensing applications of surface waves in the terahertz spectral range are discussed.
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