Equivalent Transmission Line Research Articles

Multilayer graphene-based radiation modulator for adaptive infrared camouflage with thermal management

Graphene film is a promising thermal camouflage and thermal management material because of its thin, light, flexible structural characteristics and controllable broad-spectrum electromagnetic radiation modulation properties. In this study, a thermal radiation modulator (TRM) based on multilayer graphene (MLG) was studied by simulation and an equivalent transmission line model. The physical mechanism underlying the spectral characteristics and the sensitivity of infrared (IR) radiation modulation to the number of graphene layers is revealed. Furthermore, to solve the problem of thermal instability in the MLG-based TRM, a design scheme integrating a TRM and a meta-absorber is proposed. By electrical control of the MLG, the improved modulator can achieve dynamic emissivity modulation in the wavelength ranges of 3–5 µm and 8–14 µm for adaptive thermal camouflage while maintaining a high emissivity at 5–8 µm for radiative cooling. The compatibility of tunable IR emission and radiative heat dissipation enables graphene to be used for thermal camouflage in complex environments and at high temperatures. The results not only promote the exploration of advanced thermal camouflage materials or devices but also provide inspiration for the application of graphene in thermal management, thermophotovoltaics, IR displays and communications.

A Cable Harness Routing Method Based on the Expected Maximum Crosstalk

With the increasing number of interconnected cables in electronic systems, the crosstalk between interconnected cables has played an important role in the intrasystem interference performance. However, the traditional routing method based on the shortest path cannot solve the problem of cable crosstalk. In this article, a novel cable harness routing method based on the expected maximum crosstalk is proposed. First, the closed-form expression for crosstalk based on the electrically small assumption is derived from the multiconductor transmission line (MTL) equation. According to this expression, the concept of maximum overlap length corresponding to the desired maximum crosstalk is developed. In addition, a conservative strategy is proposed to deal with higher frequency cable routing. The proposed routing method consists of the escape graph and the routing algorithm based on the maximum overlap length. A Dijkstra’s algorithm variant with the maximum overlap length as the constraint condition is proposed. The proposed method is applied to two single-ended and differential signals cable harness routing cases and compared with the traditional method to show that the routing results of the proposed method would keep the crosstalk between cable harness branches below the expected maximum crosstalk.

Microwaves as Diagnostic Tool for Pituitary Tumors: Preliminary Investigations

To date, tumors, the second cause of death worldwide, are a modern medicine plight. The development of rapid, cost-effective and reliable prevention and diagnostics tools is mandatory to support clinicians and ensure patients’ adequate intervention. Pituitary tumors are a class of neoplasm, which calls for suitable and ad hoc diagnostic tools. Recently, microwaves have gained interest as a non-ionizing, non-invasive valuable diagnostic approach for identifying pathologic tissues according to their dielectric properties. This work deals with the preliminary investigation of the feasibility of using microwaves to diagnose pituitary tumors. In particular, it focuses on benign tumors of the adenohypophysis, e.g., the pituitary adenomas. It is assumed to access the region of interest of the pituitary region by following a trans-sphenoidal approach. The problem was modeled by developing an equivalent transmission line model of the multi-layered, lossy tissues (front bone of sphenoid sinuses, air in the sinuses, posterior bone of sphenoid sinuses, the pituitary gland and the tumor). The forward problem was developed to investigate the transmission coefficient for identifying the most favorable propagation conditions. Then, it was analyzed if, by the solution of an inverse problem, it is possible to reconstruct the permittivity and electrical conductivity profiles and identify the tumor presence. The results are promising since a maximum reconstruction error of 8% is found, in the worst case, thus paving the way for the use of microwaves for the diagnosis of pituitary tumors.

Compact reconfigurable bandpass filter using quarter wavelength stubs for ultra-wideband applications

In this article, the design of a compact reconfigurable bandpass filter using quarter-wavelength open/short-ended stubs for Ultra-Wideband applications is presented. The filter has been designed using three quarter wavelength stubs. Stubs are designed for specific frequencies. At the designed frequency, the quarter-wavelength stub exhibits either bandpass or bandstop characteristics according to its short or open-circuited configuration, respectively. The proposed filter generates five passbands and twelve transmission zeros through four reconfigurable states. The direct and higher-order responses of each stub are effectively utilized to achieve five passbands, which are at 3.8 GHz – 7.8 GHz (notch band from 5.9 GHz to 6.4 GHz), 2.8 GHz − 5.9 GHz, 5.2 GHz − 8.0 GHz, 5.2 GHz – 5.88 GHz, and 1.7 GHz to 4.1 GHz. The filter is designed on FR-4 substrate and simulated in High Frequency Structure Simulator. To analytically validate the results, an equivalent transmission line circuit is extracted, and ABCD parameters have been derived. The S-parameters are derived from the ABCD parameters and plotted through MATLAB software. The designed filter is fabricated and tested. There is a good agreement between simulated and measured responses. The overall size of the filter is 24 × 15 × 0.8 mm3.

Numerical Analysis on the RF Characteristics of the Gyromagnetic Nonlinear Transmission Lines

The gyromagnetic nonlinear transmission line (GNLTL) is a special transmission line loaded with ferrite cores, which can be used as a kind of wideband high-power microwave (HPM) source due to the pulse modulation mechanism. This article carried out a series of simulations and analyses focused on the RF characteristics of GNLTL. Based on the classic transmission line model (TLM) method, a numerical model linking the transmission line equations and the microscopic magnetization dynamics equations was established. The simulations systematically studied the effects of key parameters on the output characteristics especially the RF characteristics, including the effects of transmission line geometry, excitation pulse, magnetic material, and the biasing magnetic field. The simulation results and analyses revealed that almost each parameter has effects on the output, and the effects of different parameters are different. The research introduced in this article preliminarily reveals how the output microwave varies with the parameters and provides a method to find the appropriate parameter values of a GNLTL.

Reactive Impedance Surface-Loaded Wideband Wide-Scanning Phased Array in Triangular Lattice

A phased array loaded with a reactive impedance surface (RIS) is proposed for wideband wide-scanning performance. The mushroom-like RIS structure, etched on the same printed circuit board (PCB) of the antenna, is introduced as a superstrate over the antenna aperture. The reactance of the RIS structure compensates for the scan impedance variation of the antenna during the beam scanning, explained by the equivalent transmission-line model. A superior scanning performance in all azimuth planes is achieved, and the scan blindness in the H-plane is alleviated, especially. The total compact design is capable of operating over a 2.3:1 (6 –14 GHz) bandwidth in broadside and over a 1.8:1 bandwidth in ±60° E-plane, ±70° D-plane, and ±65° H-plane scanning. The array is implemented in a triangular lattice, and edge elements in the E-plane are connected to metal walls for edge effect elimination. A 45-element ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 9$ </tex-math></inline-formula> ) array prototype is fabricated and measured. Active reflection coefficients are calculated, and scanning patterns are synthesized.

Antenna Current Calculation Based on Equivalent Transmission Line Model.

This paper provides a new way for spatial current/field profiles for frequency-selective surface analytical approximation. It confirms that the per unit length radiation resistance of an equivalent transmission line model for line antenna has little influence on the normalized current distribution. The two-wire equivalent transmission line model (typically used for transmitting line antenna) is applied to the receiving line antenna. In this case, the corresponding incident field is decomposed into odd and even mode for asymmetric distribution. A one-wire equivalent transmission line model is then introduced for any antenna composed of relative narrow strips. The incident field does not need to be decomposed. According to the simulation, the transmission line loss has little influence on the current distribution.

Analysis of Transient Response of ZPW-2000A Jointless Track Circuit Considering Frequency Variation.

In order to accurately analyze the influence of electromagnetic transient signals on the jointless track circuit when the electromagnetic transient signal propagates in the rail, it is necessary to consider the frequency-variable load terminated in the ZPW-2000A jointless track circuit and the frequency-variable loss inside the rail. A method is proposed for calculating the transient response of transmission lines system with frequency-variable end load of jointless track circuit. Firstly, the transmission lines model of jointless track circuit is established, based on multiconductor transmission lines theory, the model equation is deduced and discretized by finite difference time domain (FDTD). The vector fitting method is used to express the admittance of the tuning region in the track circuit, and the rational approximation function of the tuning region is derived from the poles, residues, and constants. The voltage and current at nodes in the tuning region are calculated by piecewise linear recursive convolution algorithm. Combined with the discrete transmission line equation, the current and voltage expression of the transient electromagnetic signal at the receiving end of the track circuit in time domain is obtained. Compared with state variable method, the error is less than 6%, which verifies the correctness of the proposed method. Finally, this paper studies the influence laws of different factors on the overvoltage at the receiving end of jointless track circuit and the weak links of jointless track circuit under the influence of transient electromagnetic signal. It provides theoretical reference for fault research and anti-interference analysis of ZPW-2000A jointless track circuit.

Stealth radome with an ultra-broad transparent window and a high selectivity transition band.

Stealth radome (SR), especially with an ultra-broad and nearly transparent window between two absorption bands, plays a crucial role in stealth techniques, antenna radomes, and so on. However, current devices have the defects of narrow transmission bands, high insertion loss, and wide transition bands between the transmission and absorption bands, which are unfavorable for the stealth of broadband radar and communication systems. In this paper, a novel SR with an ultra-broad and high-efficiency inter-absorption band transparent window is proposed by combining broadband resonance lumped circuits with a multi-layer cascaded frequency-selective surface (FSS). The equivalent circuit model (ECM) and transmission line method (TLM) are provided and analyzed as a guideline for the SR design. The SR consists of a resistive lossy layer loaded with wide passband lumped circuits and two stacked lossless FSS layers to collectively achieve the high selectivity and ultra-broad transmission band. Simulated results indicate that the proposed SR exhibits an ultra-broad passband from 8.2 to 11.2 GHz (31%) with transmission amplitude more than 0.85 and two 90% absorption bands over 6.8-7.8 GHz and 12-13 GHz, and the transition bands at both sides are only 0.4 GHz and 0.8 GHz, respectively. Our findings can stimulate the promising applications of SR in broadband stealth devices with integrated ultra-broad communication capability or in other electromagnetic (EM) compatibility facilities.

Multiband Monopole Smartphone Antenna With Bandwidth Enhancement Under Radiation of Multiple Same-Order Modes

A novel design approach to excite multiple applicable modes under an inverted-L antenna (ILA) for bandwidth enhancement is proposed. First, the working principle about how to excite multiple modes with the same order/electrical-length is theoretically investigated based on an equivalent transmission line model. Under this method, the antenna, in theory, breaks down the limitations in the number of applicable resonances and the number of available operating bands. Second, how to load parallel capacitor to shift resonant modes to the desired band is investigated, so as to achieve the enhanced-bandwidth in multiple working bands. With these arrangements, a simple dual-band ILA is proposed as an application example to highlight the merits of above approach. Herein, the same 0.25 and 0.75 wavelength modes are generated at different operating bands so that the balanced radiation performance can be well maintained at dual bands. This ILA has gained both the lower 4G band (1.71–2.69 GHz) and upper 5G band (3.3–4.2 GHz) as desired. As a result, it not only achieves two wide bandwidths of around 44.5% and 24%, but also keeps the electrically short length of around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15\lambda _{0}$ </tex-math></inline-formula> and a small clearance of 3 mm. The total efficiencies, ECC, and isolations are satisfactorily acquired for the MIMO system. All in all, it is believed that the approach proposed herein for realizing multiple resonances is a powerful alternative for multiband antennas.

Multi-wave, M-shaped rational and interaction solutions for fractional nonlinear electrical transmission line equation

In this paper, (2+1)− dimensional nonlinear fractional electrical transmission line equation (NLFETLE), which explains the wave variation in nonlinear systems, will be investigated. To convert our model into an ordinary differential equation (ODE) we adopt a conformable fractional (CF) operator. By combining exponential, polynomial, trigonometric, and hyperbolic functions, we will analyze multi-waves, periodic cross-kink, M-shaped rational and interaction solutions. We will also analyze degeneracies of hybrid waves through some graphical shapes.

A novel miniaturizedX‐bandcoplanar waveguidebranch‐linecoupler using T‐ and 𝜋‐type equivalent transmission lines

A novel miniaturized<scp>X‐band</scp>coplanar waveguide<scp>branch‐line</scp>coupler using T‐ and 𝜋‐type equivalent transmission lines

Power Changes of Electromagnetic Waves Across the Temporal Boundary in Simple Polar-Molecule Reactions

Microwave-assisted chemical reactions have been widely used, but the inhomogeneous heating limits further applications. The aim of this paper is to investigate the power transfer behavior in the simple polar-molecule reactions whose polarization changes with the proceeding of the reactions. At the temporal boundary, based on the continuity of charge and flux and the equivalent transmission line approach of the simple polar-molecule reactions, we discover the power changes in the reactions. The numerical results are in agreement with the theory of the temporal boundary. When the time scale of the component concentration variation is smaller than the wave period, the polarization is not continuous at the temporal boundary. The impedance of the reactions across the temporal boundary changes, and the reflection occurs. Moreover, when the dielectric property of the reactions decreases, the power of the waves increases after the temporal boundary and the waves experience a net energy gain. The results may be helpful in disclosing the non-uniform electromagnetic energy distribution in chemical reactions.

Analysis of waveguide polarizers using equivalent network and finite elements methods

Current research is dedicated to the development of new theoretical model for guide polarization converter with irises. New created model is derived based on the equivalent circuits and transmission line representations. Specific feature of the model consists in the possibility of account of irises thickness in the simulations by approximate single-mode method. Using equivalent lumped elements of the circuits we obtained general scattering matrices of the polarization transformer for fundamental modes of vertical and horizontal linear polarizations. Besides, numerical simulations and optimization of the device were carried out by finite elements method. Good agreement of obtained optimal sizes and polarization characteristics is observed. Provided by the polarizer phase difference between two orthogonal polarizations falls within range 90°±5° in the operating Ku-band. Calculated ellipticity coefficient is better than 1.5 dB. Developed model can be applied for designing of new waveguide polarization converters, filters and other waveguide components with irises.

On some new analytical solutions to the (2+1)-dimensional nonlinear electrical transmission line model

In the present paper, from the field of communications in physics and engineering, we select the (2+1)-dimensional nonlinear electrical transmission line equation to be studied. The model under study is one of the models that has important applications in the field of physics and telecommunications engineering. We acquire the soliton solutions by using two simple methods. We present some figures in two and three dimensions to show that these solutions actually have the properties of soliton waves.

Global Modeling of Millimeter-Wave Transistors: Analysis of Electromagnetic-Wave Propagation Effects

In this study, the transmission line concept and the electron transport theory are consolidated in a global modeling approach, the wave-electron-transport (WET) model, to account for the physical phenomena in millimeter-wave devices. No equivalent circuit model is required to represent the innate properties of the device. Hence, the model is reliable for both small- and large-signal analyses. The electrodes of a transistor act as coupled multi-conductor transmission lines at millimeter-wave bands. The WET model consists of a device solver to obtain solutions for carrier-transport equations of the intrinsic device, and an electromagnetic solver (EM solver) to provide solutions for the governing transmission lines equations. As it is crucial to transfer data between these two solvers, an interface scheme is also developed and included in the WET model. The extrinsic parameters of the device are extracted using a novel systematic technique merely based on the physical structure of the transistor. In this paper, the modeling procedure is applied to a fabricated GaN-HEMT device. Power sweep analysis has verified the accuracy of the proposed model under both linear and non-linear operations. Non-uniform voltage distribution caused by traveling waves over the electrodes is elaborately discussed to demonstrate the necessity of incorporating distributed effects.

Co‐linear polarization decoupling of two feeding ports in a single patch antenna without radiation patterns deterioration

In this paper, a novel decoupling scheme is proposed to suppress the mutual coupling between the two ports of a single patch antenna (SPA), while maintaining the radiation properties of each port with co-linear polarization, co-radiating aperture, and broadside radiation patterns without deterioration in gain. For this purpose, a pair of λ/4 nonradiative stubs are introduced and loaded symmetrically in the SPA. Thanks to the good feature that the nulls of the composite fields of TM20 and TM30 modes are present only near the coupled port, both radiating apertures of the SPA can operate simultaneously. Moreover, the decoupling principle, equivalent transmission-line models, and design guidelines are extensively illustrated. The measured results show that each port of the SPA has a broadside radiation pattern with co-linear polarization and about 7-dBi gain under isolation improvement. As such, this two-port SPA, with the size of 0.41*0.37*0.04*λ03, can be equivalent to a two-patch antenna array with 0 edge-to-edge distance. Most importantly, the proposed decoupling method is achieved without compromise in the three degrees of freedom (i.e., co-polarization, similar radiation pattern, and co-radiating aperture), which is a tough challenge nowadays. This decoupling approach allows the two-port SPA could be an alternative solution in MIMO systems or in-band full-duplex systems

A reduced-order extrapolated finite difference iterative scheme for uniform transmission line equation

In order to find the numerical solutions of the two-dimensional (2D) uniform transmission line equation, we first establish a fully second-order finite difference (FD) scheme in matrix-form and analyze the stability and convergence of the FD solutions by matrix analysis. Then we employ a proper orthogonal decomposition (POD) method to establish a reduced-order extrapolated FD (ROEFD) scheme containing very few unknowns for the 2D uniform transmission line equation and also make use of the matrix analysis to analyze the stability and convergence for the ROEFD solutions. Finally, we employ some numerical experiments to validate the effectiveness of the ROEFD scheme.

Realistic modeling of the grounding system transient behavior with frequency dependence

For better protection of electrical networks, modeling the transient behavior of grounding systems is now fundamental before the realization step. In this work we propose a new modeling approach which permits a quick and efficient analysis of the grounding systems.In the proposed approach we solve the transmission lines equations using the Finites Differences (FD) taking into account the different electromagnetic couplings that occur during the spatial discretization of the grounding electrodes. To achieve this objective we complete the general transmission lines equations by introducing the coupling terms between the different parts of the grounding system and we calculate the self and mutual per-unit length parameters according to the geometrical position of the elements (cells). We therefore use rather the term non-uniform Transmission Lines (nuTL). This new modeling offers the advantages of calculating in a single step the currents and voltages at all the points of a grounding system, also taking into account the frequency dependence. Compared to already existing full-wave electromagnetic models our modeling is realistic because its numerical implementation is simple, retains good precision and the calculation times are much reduced.

Complementary frequency selective surface pair-based intelligent spatial filters for 5G wireless systems

AbstractFrequency selective surface (FSS)-based intelligent spatial filters are capturing the eyes of the researchers by offering a dynamic behavior when exposed to the electromagnetic radiations. In this manuscript, a concept of creating complementary structures which stems from Babinet’s principle is illustrated. A hybrid complementary pair of FSS (CPFSS) comprising double square loop FSS (DSLFSS) and double square slot FSS (DSSFSS) on either side of the dielectric substrate is proposed. DSLFSS offers band-pass behavior and can be placed as a superstrate, whereas DSSFSS behaves as a band-stop intelligent spatial filter that blocks the radiations falling on it, thus making them applicable for use as a substrate. The technique utilized for analyzing DSLFSS and DSSFSS structures is based on the equivalent circuit modeling and transmission line methodology. The CPFSS structure offers the design simplicity, hence, suitable for placing them with the printed patch antenna radiators in wireless networking devices operating in sub-6 GHz 5G spectrum. DSLFSS offers band-pass behavior ranging from 2.99 to 5.56 GHz, whereas DSSFSS offers band-stop behavior ranging from 2.85 to 5.42 GHz covering all n77 (3.3–4.2 GHz), n78 (3.3–3.8 GHz), and n79 (4.4–5 GHz) bands of FR1 spectrum of sub-6 GHz 5G range. The passband and the stopband offered by the two structures of CPFSS geometry are stable to oblique angles of incidence and the proposed design also offers polarization-independent behavior. The thickness of the dielectric region existing within the pair of designed structures is critical for the location of the passbands and the stopbands. The impact of the overall thickness of the dielectric substrate on the passbands and stopbands is also reported in this article.