Equivalent Transmission Line Research Articles

Wideband and Large Angle Electromagnetically Induced Transparency by the Equivalent Transmission Line in a Metasurface

A classical structure for a U-shaped metasurface exhibiting a wideband and large angle electromagnetically induced transparency (EIT) effect in the terahertz range is proposed. One horizontal and two vertical strips, which represent the bright and dark modes, respectively, are created for the U-shaped structure. The finite integration time domain (FITD) and equivalent circuit method are compared with the EIT result. The EIT effect is affected by the length of the vertical bar and by the distance from the vertical bar to the symmetry axis. The results show that the asymmetry of the main structure in the x and y axes makes it easier to achieve the EIT effect. In addition, by changing the incident angle, the EIT effect always exists until the angle of the incidental electromagnetic wave is 85 degrees. These results have many potential applications for terahertz filtering, large-angle switching and sensors.

A TM30-/TM40-Mode Pattern-Reconfigurable Microstrip Patch Antenna for Wide Beam Coverage

A novel two-state multi-lobe pattern-reconfigurable microstrip patch antenna (MPA) for wide beam coverage is proposed, where two states are realized by two higher modes, and a multi-lobe pattern is employed for each state. First, the equivalent transmission line model is used to analyze the input impedances of the dual-mode MPA. By adjusting sizes of the capacitive coupling patches and profile of the MPA, the frequency bands of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> modes are controlled, yielding a band intersection. Second, by controlling the length of the radiating patch, the beam-level differences of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> -mode and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> -mode patterns are reduced, respectively. Third, two parasitic patches are also loaded. As a result, the mode-gain difference between TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> modes is small, and all the beam overlap levels are higher than -3 dB. The measured results show that the 3 dB beam coverage of the MPA at 2.9 GHz ranges from -68° to +73° in the xoz plane, and its maximum gain is 7.0 dBi. Furthermore, the two-state pattern-reconfigurable MPA has a 3-lobe pattern pointing at {0°, ±37°} for the first state and a four-lobe pattern pointing at {±17°, ±58°} for the second state. The measured results are in good agreement with the simulated ones.

Numerical investigation on signal transmission characteristic of electromagnetic measurement-while-drilling in underground coal mine

Signal transmission characteristic research of electromagnetic measurement-while-drilling is the theory basis for its application in underground coal mine drilling. However, the existing numerical models of signal transmission are conducted on oil and gas drilling. In this study, based on the equivalent transmission line theory, a numerical model considering the nearly horizontal signal channel for signal transmission in underground coal mine was proposed. Then, factors affecting the received signal strength, including hole depth, coal seam resistivity, excitation voltage and received distance were investigated. Results indicate that received signal strength decreases with the increase of hole depth and decrease of coal seam resistivity, and increasing excitation voltage and orifice received distance reasonably is an effective method to enhance received signal strength.

A Novel Meander Split Power/Ground Plane Reducing Crosstalk of Traces Crossing Over

In this paper, a novel meander split power/ground plane is proposed for reducing crosstalk between parallel lines crossing over it. The working mechanism of the meander split scheme is investigated by simulations and measurements. The LC equivalent circuit and transmission line model are developed for modeling interactions between the meander split and the signal lines. The proposed meander structure enhances electromagnetic coupling between split planes. The capacitive coupling across the split ensures signal integrity and magnetic coupling between adjacent finger shaped structures suppresses lateral wave propagation along the split gap, which in turn helps suppress the crosstalk. The effectiveness of the meander split remains valid over very wide frequency ranges (up to 9 GHz). Experimental results show that the proposed structure improves the signal quality and reduces the near/far end crosstalk over 30 dB and 50% in the frequency domain and time domain, respectively.

Compact ultrathin conformal metamaterial dual‐band absorber for curved surfaces

A compact, ultrathin conformal metamaterial dual-band absorber for curved surfaces has been presented in this article. The absorber unit cell composed of circular and split ring resonators which are connected with plus-shaped structure. The proposed absorber unit cell is compact in size (0.22λo × 0.22λo) and as well as ultrathin thickness (0.006λo), where λo is the wavelength at 5.8 GHz. The designed absorber gives two absorption tips at 5.8 and 7.7 GHz with more than 90% absorptivity. The full width at half maximum bandwidths are 220 MHz (5.67-5.89 GHz) and 250 MHz (7.58-7.83 GHz). The proposed conformal absorber is sensitive to the polarization angle and has a stable absorptivity over a wide range of incident electromagnetic wave. The parametric analysis and equivalent transmission line model have been investigated. The surface current and electric field distribution also discussed for understanding the absorption mechanism. To analyze the performance of proposed absorber on the curved surfaces, it is wrapped on the different radius of cylindrical surface and measured the absorptivity. Simulated and measured results have good agreement between them.

Research and application of the FETD method for the EM transient response of MTLs excited by HEMP

An efficient field-to-line coupling model in the time domain is developed combining the second-order decoupled multiconductor transmission lines (MTLs) equations and the finite-element time-domain (FETD) method for evaluating the electromagnetic (EM) transient response of MTLs over a lossy ground excited by a high-altitude EM pulse (HEMP). First, the incident HEMP electric fields on the lines are calculated as equivalent distributed sources introduced into the MTLs equations. Then, the discrete FETD equations for the lines against the HEMP, in which the effect of frequency-dependent parameters caused by the ground impedance is considered, are derived using the FETD method with current as the single iteration variable. Finally, the transient currents induced on the lines are obtained by assembling all the discrete FETD equations into the global FETD equation, and the transient induced voltages on the lines are calculated by discretising the coupled equations with respect to current and voltage. The proposed model is successfully compared with the finite-difference time-domain method via several examples. It is then employed to analyse the effect of various parameters on the transient currents including the polarisation and the incident angles of the HEMP, the conductivity, and the relative permittivity of the soil.

The Ultra-Low-k Dielectric Materials for Performance Improvement in Coupled Multilayer Graphene Nanoribbon Interconnects

The ultra-low-k dielectric material replacing the conventional SiO2 dielectric medium in coupled multilayer graphene nanoribbon (MLGNR) interconnects is presented. An equivalent distributed transmission line model of coupled MLGNR interconnects is established to derive the analytical expressions of crosstalk delay, transfer gain, and noise output for 7.5 nm technology node at global level, which take the in-phase and out-of-phase crosstalk into account. The results show that by replacing the SiO2 dielectric mediums with the nanoglass, the maximum reduction of delay time and peak noise voltage are 25.202 ns and 0.102 V for an interconnect length of 3000 µm, respectively. It is demonstrated that the ultra-low-k dielectric materials can significantly reduce delay time and crosstalk noise and increase transfer gain compared with the conventional SiO2 dielectric medium. Moreover, it is found that the coupled MLGNR interconnect under out-of-phase mode has a larger crosstalk delay and a lesser transfer gain than that under in-phase mode, and the peak noise voltage increases with the increase of the coupled MLGNR interconnect length. The results presented in this paper would be useful to aid in the enhancement of performance of on-chip interconnects and provide guidelines for signal characteristic analysis of MLGNR interconnects.

Equivalent Circuit Models of Finite Slot Antennas

We present a systematic approach to describe planar slot antennas embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semiinfinite or finite slots, fed by a delta-gap excitation. The solution entails only two basis functions, one located at the feed and the other at the termination. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end points. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end points: the reactances account for the reactive nature of the feed and the termination, while the resistances represent the radiated space waves, emerging from both the feed and the end points. This procedure can be used to derive the input impedance of planar slot antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot.

SPICE‐compatible admittance equivalent circuit for stochastic transmission line under external field illumination

For the stochastic transient analysis of transmission line with parameter uncertainties under plane wave illumination, a random admittance equivalent circuit model was presented. Based on the polynomial chaos theory and stochastic Galerkin method, the random transmission line equation was cast into the augmented deterministic transmission line equation. By virtue of eigenfunction decomposition and appropriate acceleration of convergence, a SPICE-compatible Foster form of admittance equivalent circuit model was obtained. The random boundary condition for non-linear loads was solved by applying the Gauss quadrature rule. Application examples validate the accuracy and efficiency of the presented methodology.

Miniaturised microstrip patch design based on highly capacitive defected ground structure with fractal boundary for X‐band microwave communications

This article proposes a new class of miniaturised microstrip patch design for wireless communications at 10 GHz. Antenna miniaturisation is achieved here by loading a highly capacitive modified Minkowski fractal (type-2) defected ground structure (MFDGS-II) exactly beneath the center of the radiating patch. The proposed methodology involves sensitivity analysis to select best DGS configuration. The resonant frequency corresponding to the patch is reduced from 16.832 GHz to 10 GHz incorporating MFDGS-II without any change in the physical size of the antenna. This enables a patch size reduction of as high as 68% and an overall volumetric reduction of 84% along with an improvement in bandwidth and efficiency of the antenna. A prototype of the proposed antenna is fabricated, and its performance parameters are measured. An equivalent transmission-line model is presented to explain the theoretical background behind the shift in the resonant frequency of the antenna. Our antenna prototype with a lower patch size of 0.20 λ 0 × 0.15 λ 0 , exhibits an impedance bandwidth of 270 MHz, a realised gain of 3.2 dBi with radiation efficiency of 98% centered at 10 GHz. The proposed compact antenna has the potential to meet the practical requirements for portable X-band wireless sensor applications.

An efficient SPICE-compatible circuit model for transmission line response excited by an electrically short dipole inside a metallic cavity

ABSTRACTFor the transmission line response excited by an electrically short dipole inside a rectangular cavity, a SPICE-compatible broadband Foster type equivalent circuit is presented. The electric field inside a cavity is represented by the eigenmode decomposition of Helmholtz equation, while the current of transmission line is expanded using the eigenmode of transmission line equation. The field-to-line coupling effect is described by the Agrawal formula. The convergence of the circuit is accelerated by the extraction of quasi-static inductances and capacitances. The validity and efficiency of the presented method is verified both in frequency and time domain. Also, the effects of lossy filling material are discussed. Besides, in order to show the aggravation effect of metallic cavity on the electromagnetic interference, the induced currents on the transmission line with and without a metallic casing are given and compared.

Design of Checkerboard AMC Structure for Wideband RCS Reduction

In this paper, we propose a method for designing checkerboard surfaces using strategically placed artificial magnetic conductors (AMCs) for wideband radar cross section (RCS) reduction. The theoretical analysis shows that the reflection phases of the two AMCs should be linear. The cancelation conditions of checkerboard structure are analytically derived using an equivalent transmission line model, and the ideal impedance conditions of the two AMCs are obtained, which serve as guidance to select patterns of two AMCs unit. A planar checkerboard surface with two kinds of AMC elements is designed for wideband RCS reduction. A 10 dB RCS reduction is observed for approximately 91.5% of the relative bandwidth (3.77–10.14 GHz) under normal incidence. A prototype of the proposed checkerboard surface is fabricated, and the measurements results show good coincidence with the synthetic studies. The bistatic RCS of the checkerboard surface is considered for both transverse electric and transverse magnetic polarizations under oblique incidence.

On the resonant frequencies of dual‐band patch antennas

A square patch radiator supports both TM 01 and TM 10 modes with equal resonant frequencies. Feeding the patch in its diagonal can excite both modes with equal amplitudes and phases. By utilising this property, an effective technique is proposed to realise dual-band dual-polarised patch antenna. While the lower resonant frequency can be calculated using an existing analytical formula, an expression of the higher resonant frequency is still missing in the literature. To this end, an approximate expression of the higher resonant frequency is devised using the equivalent transmission line model in this work. It is a function of the distance between the shorting post and the feeding location. In order to validate the accuracy of the expression, three different antenna configurations are designed and manufactured. Good agreements between theoretical, simulated, and measured results are observed.

The Design of Optical Circuit-Analog Absorbers through Electrically Small Nanoparticles

In the last few years, the perfect absorption of light has become an important research topic due to its dramatic impact in photovoltaics, photodetectors, color filters and thermal emitters. While broadband optical absorption is relatively easy to achieve using bulky devices, today there is a strong need and interest in achieving the same effects by employing nanometric structures that are compatible with modern nanophotonic components. In this paper, we propose a general procedure to design broadband nanometer-scale absorbers working in the optical spectrum. The proposed devices, which can be considered an extension to optics of microwave circuit-analog absorbers, consist of several layers containing arrays of elongated nanoparticles, whose dimensions are engineered to control both the absorption level and the operational bandwidth. By combining a surface-impedance homogenization and an equivalent transmission-line formalism, we define a general analytical procedure that can be employed to achieve a final working design. As a relevant example, we show that the proposed approach allows designing an optical absorber exhibiting a 20% fractional bandwidth on a thickness of λ/4 at the central frequency of operation. Full-wave results confirming the effectiveness of the analytical findings, as well as some considerations about the experimental realization of the proposed devices are provided.

A MPI-Based Parallel FDTD-TL Method for the EMI Analysis of Transmission Lines in Cavity Excited by Ambient Wave

At present, the existing electromagnetic interference (EMI) analysis methods for the cavity with transmission lines (TLs) often need a large number of meshes to satisfy certain accuracy, which would seriously affect the calculation time, memory, and efficiency. Therefore, this paper presents a time-domain parallel method consisting of finite-difference time-domain method, TL equations, and message passing interface library. This method has two obvious advantages: one is that it does not need to mesh the TLs, which can reduce a lot of computational memory; and the other is that it can run on multiple processors or computers to save a lot of computational time. In order to verify the accuracy and validity of this method, the intracavity transmission of multiconductor TLs and coaxial cable under ambient wave excitation is simulated numerically and compared with the traditional method. The results show that the method can be well applied for the EMI analysis of the TLs in cavity under ambient excitation.

Analytical studies on waves in nonlinear transmission line media

In this study, we introduce the lossy nonlinear transmission line equation, which is the dissipative-dispersive equation and an important problem of electrical transmission lines. For the engineers and physicist, the equation and its exact solutions are important so to obtain the exact solutions; one of the modifications of auxiliary equation method based on Chebyshev differential equation is studied. The results are discussed and given in details. Recently, the studies of lossy transmission line equation have been challenging, thus, it is believed that the proposed solutions will be key part of further studies for waves in nonlinear transmission line media, which has mixed dissipative-dispersive behavior.

Novel synthesis formulas to design square patch frequency selective surface absorber based on equivalent circuit model

A new procedure is presented to design electromagnetic absorbers based on resistive square patch frequency selective surface (FSS) over grounded dielectric. The periodicity (p) and the distance between two adjacent squares in the lattice (w) are two unknowns to be solved, given the thickness and permittivity of the substrate, surface impedance of the square patches and the desired reflectivity in some specified frequency. Equivalent circuit model and transmission line method are employed here. Previously reported analysis formulas to calculate the square patch FSS admittance are exploited and novel synthesis formulas are extracted based of them. The final synthesis equations to calculate p and w are presented in term of polynomials. Usually an absorber is supposed to have a maximum reflectivity r in a frequency band [f1, f2]. The (p, w) pairs for reflectivity less than r in f1, define an area in p-w plane. The intersection of the so-called area with the similar one defined by f2 specifies all possible (p, w) pairs. Finally the results are tested and verified by the commercial full wave simulator Ansys-HFSS as well as some experimental design. There is a good agreement between the expected results with the full wave analysis and practical test.

Transmission line method for the simulation of fiber Bragg gratings.

A new method for the analysis and design of fiber Bragg gratings (FBGs) based on the theory of transmission lines has been developed and verified both theoretically and experimentally. The method is an extension of the coupled-mode theory and utilizes the equivalent transmission lines in order to simulate any type of grating, with an easy and direct implementation. The method provides the ability to analyze the optical devices without using full wave approaches, while also facilitating the incorporation of core materials with a complex or non-linear refractive index, non-uniform distributions of the grating's refractive index, and tilted and phase-shifted gratings. The approach also allows the design of the grating for a given reflection spectra. Numerical results of the method's application on a randomly varied inscription of the refractive index of a FBG have also been simulated and discussed. Using this method, the characteristics of an erbium-doped (ED)-FBG have been simulated and the predictions verified experimentally.

METHOD OF STRIP LINES’ TE MODES CHARACTERISTICS CALCULATION

The paper is devoted to the calculation of the electromagnetic field in a stripline based transmission line for the TE-modes. TE-mode is one of the closest to the main mode, especially at the high frequencies, and should be considered in the multiple-mode resonators. Moreover, TE-mode is the main mode in the slotline at ane frequency. The method of solving the electromagnetic field problem of computing the characteristics of TE-modes of the slotlines is proposed. The proposed method is based on a rigorous electrodynamic approach and has no restrictions on the geometric and electrophysical parameters of the lines. The problem is reduced to the eigenvalues and eigenvectors problem, which is solved by the 2D finite element method applied to the cross-section of the line. The resulting solutions provide the possibility of obtaining the distribution of the component of the electromagnetic field and calculate the integral characteristics of the stripline, such as effective dielectric permittivity, which defines wavelength in the line, and characteristic impedance, which describes the relation between current and voltage in the equivalent transmission line. The distribution of the electric field components in the slotline is shown. The results of the effective dielectric permittivity and characteristic impedance calculation for the slotline with various geometrical and electrophysical parameters at different operating frequencies are presented. The obtained values of the effective parameters are in good agreement with other known calculated and measured results. The proposed method can be applied to any structures of strip lines in an arbitrary medium with any dielectric or metal objects placed near the line. Thus, such a method is suitable for the analysis and design of micro mechanically tunable devices as well.

The antireflective properties of DMSO-doped-PEDOT:PSS films at THz frequencies

The antireflective properties of DMSO-doped poly (3,4-ethylenedioxythiophene):poly (4-styrenesulfonate) (PEDOT:PSS) thin films produced by spin coating at THz frequencies is reported. The reflected pulses from the silicon substrate are observed to change with the doping concentrate and the thickness of the DMSO-doped-PEDOT:PSS films. Theoretical analysis based on an equivalent transmission line circuit model has been used to understand the experimental results. Excellent antireflective properties is achieved by 10 vol% DMOS-doped-PEDOT:PSS films. The normalized main pulse transmittance remains as high as 70%, and the minimum reflected pulse transmittance is only 3% at 0.52 THz. This work paves the way for PEDOT:PSS-based THz antireflection coating.