Transmission Line Equivalent Circuit Research Articles

A Design Method and Application of Meta-Surface-Based Arbitrary Passband Filter for Terahertz Communication.

A meta-surface-based arbitrary bandwidth filter realization method for terahertz (THz) future communications is presented. The approach involves integrating a meta-surface-based bandstop filter into an ultra-wideband (UWB) bandpass filter and adjusting the operating frequency range of the meta-surface bandstop filter to realize the design of arbitrary bandwidth filters. It effectively addresses the complexity of designing traditional arbitrary bandwidth filters and the challenges in achieving impedance matching. To underscore its practicality, the paper employs silicon substrate integrated gap waveguide (SSIGW) and this method to craft a THz filter. To begin, design equations for electromagnetic band gap (EBG) structures were developed in accordance with the requirements of through-silicon via (TSV) and applied to the design of the SSIGW. Subsequently, this article employs equivalent transmission line models and equivalent circuits to conduct theoretical analyses for both the UWB passband and the meta-surface stopband portions. The proposed THz filter boasts a center frequency of 0.151 THz, a relative bandwidth of 6.9%, insertion loss below 0.68 dB, and stopbands exceeding 20 GHz in both upper and lower ranges. The in-band group delay is 0.119 ± 0.048 ns. Compared to reported THz filters, the SSIGW filter boasts advantages such as low loss and minimal delay, making it even more suitable for future wireless communication.

An efficient and accurate semi-analytical matching technique for waveguide-fed antennas

Several RF and microwave radiating devices, such as horn antennas, Fabry–Perot cavity antennas, and aperture-fed focusing devices, are excited through rectangular waveguides. The impedance matching of the overall system (from the waveguide feed to the radiating aperture) is a task of crucial importance that is often addressed by means of brute-force parameter-sweep full-wave analyses or blind optimization algorithms. In both cases, a significant amount of memory and time resources are required. For this purpose, we propose here a simple, yet effective solution, which only requires a single full-wave simulation and a semi-analytical procedure. The former is used to retrieve the antenna input impedance at the end of the waveguide port excitation. The semi-analytical procedure consists in a transmission-line equivalent circuit that models two waveguide discontinuities (namely two capacitive irises) within the waveguide section, whose position and geometric features are finely tuned to obtain a satisfactory impedance matching around the working frequency. The proposed method is shown to be effective in diverse and attractive application-oriented contexts, from the impedance matching of a Fabry–Perot cavity antenna to that of a wireless near-field link between two aperture-fed focusing devices. A remarkable agreement between full-wave simulations and numerical results is found in all cases. Thanks to its versatility, simplicity, and a rather low demand of computational resources, the proposed approach may become an essential tool for the effective design of waveguide-fed antennas.

Stepped Impedance Optimum Short-Circuited Stub 1–6 GHz and 6–10 GHz Bandpass Filters for Multi-standard Radio

This article presents two ultra-broadband bandpass filter (BPF) designs for multi-standard applications, operating from 1–6 GHz and 6–10 GHz, with wide stopband characteristics. 1–6 GHz BPF (Filter 1) is based on the circuit model for an optimum distributed bandpass filter consisting of 3 shunt short-circuited stubs separated by non-redundant unit elements. By varying the length ratio between the unit elements and stubs and introducing stepped impedance in the unit elements, a 143% fractional bandwidth (FBW) is achieved, which is 20% higher than that obtained through the conventional optimum shunt short-circuited stub method. In addition, a stepped impedance elliptic lowpass filter was cascaded to achieve wide stopband characteristics from 7 GHz to 20 GHz. Filter 2 (6–10 GHz) is constructed by cascading a shunt short-circuited stub optimum high pass filter having a stepped impedance unit element with a stepped impedance low pass filter. The analytical model, transmission line equivalent circuit model, and full wave electromagnetic simulated model are presented along with the measured results. The measured in-band return loss of Filter 1 and Filter 2 is >12 dB, and the measured insertion loss is < 2 dB. The measured group delay of Filter 1 and Filter 2 is <0.8 ns.

Effect of binder on the electrochemical performance of activated carbon electrodes obtained from waste hazelnut shells: Comparison of PTFE and PVDF

In this study, the electrochemical performance of the electrode materials based on two commonly used binders –poly(vinylidene difluoride) (PVDF) and poly(tetrafluoroethylene) (PTFE)– was introduced. The electrochemical performance of the activated carbon electrodes was explored by performing cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. The results showed that the activated carbon electrode prepared at 500 °C with PTFE (AC-500-PTFE) exhibited higher capacitance values at low current rates than the one with PVDF (AC-500-PVDF). The results also revealed that the capacitance values of the AC-500-PVDF electrode for the current rates higher than 1.5 A g−1 were higher than the AC-500-PTFE electrode. The implemented transmission line equivalent circuit model for impedance showed that the capacitance inside the pores was higher for the AC-500-PVDF, and the higher capacitance on the electrode surface was obtained for the AC-500-PTFE. As a result, it is recommended to prefer PTFE binder for low current density, yet a PVDF binder for high current density applications.

Universal approach for diffusion quantification applied to lead halide perovskite single crystals

A universal approach to calculating diffusion coefficients in lead halide perovskite single crystals, which have ionic and mixed ionic–electronic conductivity, is proposed. Using impedance spectroscopy, it is demonstrated how to model a non-ideal Warburg element and transmission line equivalent circuit to identify ionic diffusion in the material. The proposed method is applicable to samples of any thickness and electrical properties. Additionally, it is shown how to overcome the challenges of low-frequency impedance measurement and the non-ideal behavior of the elements through extrapolative modeling and approximation.

A novel broadband l inear‐cross and l inear‐circular reflective polarizer based on interdigital capacitance loaded dipole for radar cross‐section applications

A novel interdigital capacitance (IDC) frequency selective surface (FSS) based linear-cross reflective polarizer for K- and Ka-band applications is demonstrated in this work. The suggested device includes an IDC-loaded dipole printed on a thin FR-4 grounded dielectric substrate. From 17.02 to 37.30 GHz, it shows linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) of 20.28 GHz bandwidth (74.7% fractional bandwidth [FBW]) for a y/x polarized incident electromagnetic (EM) wave. Along with linear-cross conversion, this polarizer also performs linear-circular conversions with axial ratio ≤ 3 dB in two frequency bands (Ku band-right circular, 15.13–16.15 GHz; Ka-band-left circular, 38.52–39.78 GHz) with 6.52%, and 3.14% FBW, respectively. The design performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) modes. The polarizer unitcell has structural dimensions 0.177 × 0.177 × 0.061 λ L 3 , $$ {\boldsymbol{\lambda}}_{\boldsymbol{L}}^{\mathbf{3}}, $$ where λL corresponds to the free-space wavelength of the lowest working frequency. The polariser's transmission line equivalent circuit model is extracted, and a good match is observed with the EM solver response. The broadband behavior of FSS and the ground plane is better understood by looking at surface current patterns at resonant frequencies. The proposed design's radar cross-section (RCS) analysis is compared to perfect electric conductor for the bistatic condition. The design novelty lies in its compact architectural volume of the unitcell 1.911 ( λ L 3 / 1000 $$ \Big({\boldsymbol{\lambda}}_{\boldsymbol{L}}^{\mathbf{3}}/\mathbf{1000} $$ ), low-profile, broadband PCR response with superior angle stability, dual-polarization conversion with circular rotation switching makes it a good option for real-time applications.

An Equivalent Circuit/System by Design Approach to the Design of Reflection-Type Dual-Band Circular Polarizers

A dual-band reflection-mode wide-bandwidth and wide-angle scanning circular polarizer is designed. The proposed polarizer can convert linearly polarized waves into right- and left-hand circularly polarized (RHCP and LHCP) waves in the two separate nonadjacent receiving and transmitting K/Ka frequency bands. The polarizer is based on dual-layer dipole arrays printed on both sides of a dielectric substrate separated by a second substrate from the ground plane. An analytic model based on transmission line equivalent circuits is developed. Closed-form expressions are derived to demonstrate the operating principle providing a simple design procedure. The proposed model can be used to optimize the converter for a specific propagation angle of the incident wave. Finally, a system-by-design (SbD) strategy is proposed to improve the performance of analytically synthesized devices. Toward this goal, a computationally efficient “digital twin” of the accurate full-wave model is built to speed up the solution space exploration and efficiently reach the global optimum. A prototype is designed for the incident angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta _{0} = 30^{\circ }$ </tex-math></inline-formula> and it is shown that the axial ratio lower than 3 dB is maintained for a wide-angle field of view of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \theta = 60^{\circ }$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\theta }_{min}=0^{\circ },{\theta }_{max}=60^{\circ }$ </tex-math></inline-formula> ) in both frequency bands.

Exploring point defects and trap states in undoped SrTiO3 single crystals

The defect chemistry and electronic trapping energies in undoped single crystalline SrTiO3 were examined by electrochemical impedance spectroscopy at low (25–160 °C) and intermediate (500–700 °C) temperatures. Electronic and ionic conductivity as well as chemical capacitance values were obtained with a transmission line equivalent circuit. Impedance spectroscopy at low temperatures was used to quantify trapping energies of main ionic defects. Particularly the chemical capacitance is shown to be a highly valuable, though hardly used tool for establishing a defect model based solely on electrochemical measurements. It is very sensitive for minority charge carriers and can thus unveil otherwise hardly accessible defect concentrations. The chemical capacitance analysis yields a valence dependent acceptor concentration in the ppm range for the investigated samples. Complementary positron annihilation lifetime spectroscopy (PALS) suggests existence of Ti vacancies and both methods (chemical capacitance and PALS) agree in their quantification of the corresponding vacancy concentration (6 ppm). Beyond successfully predicting acceptor defect concentrations in undoped SrTiO3, the method is sensitive for electronically relevant defects in sub-ppm concentrations.

Compact, broadband, wide angular stable circuit analog absorber at sub‐6 GHz for radar cross section reduction

AbstractThis work presents a compact broadband wide angular stable polarization‐insensitive circuit analog absorber at sub 6 GHz. It shows almost 95% absorption from 2.26 to 5.76 GHz over the entire operating range. A transmission line equivalent circuit is modeled, and the response is validated. The design is obliquely stable up to 45° for both transverse electric and transverse magnetic incidences. The analysis of surface current distributions at two resonant frequencies confirming magnetic resonances' role in near‐unity absorption. It is compact with a periodicity of 0.1 λL and thickness of 0.08 λL. Finally, bistatic radar cross section reduction of the proposed absorber attached with an antenna is measured.

Adaptive Single-Phase Auto-Reclosing Approach for Shunt Compensated Transmission Lines

Single-phase auto-reclosing (AR) scheme is widely employed in extra high voltage (EHV) transmission networks to quench transient faults without completely removing the faulted transmission line (TL). Long EHV TLs are commonly equipped with shunt reactors to reduce the Ferranti effect overvoltages. It is common practice to disconnect these reactors under the heavy load periods during the year. Considering this point, the AR technique should be able to work properly not only when the TL shunt reactors are in service, but also when they are disconnected. This paper puts forward a novel adaptive single-phase AR approach for shunt compensated TLs based on the general mathematical model of faulted phase voltage waveform after the line isolation, which is obtained by analytical analysis conducted on the TL's equivalent circuit. The effect of capacitor voltage transformer (CVT) on the voltage measurement is taken into account using a proper model for the CVT. Performing some data processing on the faulted phase measured voltage, useful features are extracted which are used by the support vector machine classifier to reliably detect the arc extinction instant. The proposed approach performance is evaluated by extensive simulation studies, accounting for different TL compensation schemes, transposition configurations, and arc conditions.

Corrosion Behavior of Zinc Covered with Native Oxides Under Thin Solution Films

This study clarified the influence of native oxides on the atmospheric corrosion of Zn. The electrochemical impedance spectroscopy (EIS) values of native-oxide-covered Zn were measured under thin solution films of 10 μm to 500 μm in thickness. The native oxides were formed by exposing pure Zn plates to humidified air at two different temperatures, 25°C and 60°C, for the duration of one week. EIS was applied to the native-oxide-covered Zn for measurement under thin solution films; the results were analyzed using a transmission line equivalent circuit to determine the charge-transfer resistance (Rct). The native oxide formed at 25°C strongly suppressed the corrosion rate (1/Rct) of Zn, which was independent of the solution film thickness (Xf). However, the 1/Rct was not reduced by the native oxides formed at 60°C, as it was dependent on Xf. This paper discusses the different behaviors of the native oxides in the context of corrosion protection.

Electrochemical Impedance Analysis of SOFC with Transmission Line Model Using Distribution of Relaxation Times (DRT)

In this work, electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis were used to evaluate the performance determining parameters for a solid-oxide fuel and electrolysis cell. The SOFC/EC was formulated with 8 mol% Yttria-stabilized zirconia (YSZ) electrolyte sandwiched between Ni-YSZ fuel electrode and La0.6Sr0.4Co0.2Fe0.8O3-10mol% gadolinium doped ceria (LSCF6428-GDC10, 5:5) composite air electrode. To deconvolute the multistep elementary reactions at both of the electrodes, EIS was measured as a function of temperature (775 °C–850 °C), gas compositions, and gas flow rates (50–200 sccm). Concurrently, DRT analysis was employed to resolve frequency-dependent electrode reactions effectively. From the DRT analysis, multistep elementary reactions at fuel and air electrode were separated and corresponded to a transmission line equivalent circuit model with parameters ( ). Finally, the cell performance limiting factors such as apparent diffusivity (), surface reaction constant (), and effective lengths () of each electrode were determined.

Free-Standing Carbon Electrodes for the Oxygen Evolution Reaction

N-functionalized hydrothermal carbon materials (N-HTC) with spherical morphology were prepared by hydrothermal synthesis utilizing glucose and urotropine as starting materials, which makes the synthesis cost-efficient, environmental friendly and allows simple scale-up. The molar ratio of glucose and urotropine has been varied and the powder materials were pelletized, resulting in mechanically stable disc electrodes. By increasing the amount of nitrogen, N-contents from 5 wt% up to maximal 8 wt% were obtained after pyrolysis at 1000 °C. The pellet can then be used as an anode for alkaline water splitting. In literature, there are still no direct evidence of metal-free carbon as electrocatalyst for oxygen evolution reaction. By comparing the N-functionalized sample and without functionalization, we found that the former has superior stability under water splitting condition (relative high potential). Up to one week of stable oxygen production was achieved. The result indicates that nitrogen facilitates oxygen evolution reaction. Besides, the nitrogen species also hinders carbon corrosion, proved by a simple Hoffmann cell measurement. Pellets with different synthesis condition as well as nitrogen content are compared in order to get the optimized synthesis condition. For better understanding, methylene blue adsorption and mercury intrusion porosimetry are used to characterize the pore structure of the carbon materials. The relative work function and conductivity of the carbon pellet are determined by Kelvin-probe and Van-der-Pauw methods, respectively. A conventional three-electrode assembly is used to characterize the electrochemical performance, including activity, stability as well as mass transport property by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy (EIS). A transmission line equivalent circuit model is used to fit the EIS complex spectra, where the diffusion resistance and reaction resistance can be determined. The two resistances are very important reaction key performance indicator for oxygen evolution reaction, as it can distinguish a diffusion process from a reaction. The gas products as well as electrolyte after electrochemical test can be analysed by mass spectrometry, ESI-MS, UV-VIS spectroscopy, etc. From the mass spectrometry results, the mole fraction of oxygen in the total product gas can be determined, determining the selectivity of the reaction. Besides, water diffusion NMR measurements before and after electrochemical test shows changes in the water interaction, which can be correlated to Nitrogen species changes in the electrode. This study demonstrates that N-functionalization improves the stability of HTC for oxygen evolution reaction providing a promising pathway for the future energy conversion and storage.

Insight into the corrosion evolution of Fe-based amorphous coatings under wet-dry cyclic conditions

Understanding the corrosion behavior of Fe-based amorphous coatings under wet-dry cyclic conditions is of pretty importance for coating applications in marine environments. In this paper, the corrosion evolutions of the coatings under wet-dry cyclic conditions were investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Accurate charge transfer resistance (Rt) was obtained through fitting EIS results using a modified transmission line equivalent circuit model and a landscape map of Rt was constructed for a panoramic investigation on coating corrosion. The results show that the corrosion rate of the coating changes cyclically under wet-dry cyclic conditions. Corrosion within a single wet-dry cycle can be presented as four stages: an initial decrease of corrosion rate due to passivation or repassivation when the coating is wetted, then a slow increase due to concentrated aggressive ions with solution evaporation, followed by a rapid increment associated with fast oxygen transport under ultrathin solution film and finally a stable stage as solution dries out. It is deduced that an oxygen concentration gradient can form between the inside and the outside of coating pores when the solution film over the coating is very thin, which further promotes the localized corrosion in the pores. According to the landscape map of Rt, the coating maintains its high corrosion resistance for the initial 33 wet-dry cycles. But its corrosion resistance decreases significantly in the 35th wet-dry cycle accompanied by the attack of localized corrosion. After 65 wet dry cycles, the coating fails due to the penetration of localized corrosion. The interparticle oxide layers are defective, which enhances the localized corrosion process.

Quantification of Ionic Diffusion in Lead Halide Perovskite Single Crystals

Lead halide perovskites are mixed electronic–ionic semiconductors that have recently revolutionized the photovoltaics field. The physical characterization of the ionic conductivity has been rather elusive because of the high intermixing of ionic and electronic current. In this work, the synthesis of low defect density monocrystalline MAPbBr3 (MA = methylammonium) solar cells free of a hole transport layer (HTL) suppresses the effect of electronic current. Impedance spectroscopy reveals the characteristic signature of ionic diffusion (the Warburg element and transmission line equivalent circuit) and ion accumulation at the interface of MAPbBr3 with the external contacts. Diffusion coefficients are calculated based on a good correlation between thickness of MAPbBr3 and characteristic diffusion transition frequency. In addition, reactive external interfaces are studied by comparison of polycrystalline MAPbBr3 devices prepared either with or without a HTL. The low-frequency response in impedance spectroscopy ...

EIS of Zinc Under Thin Solution Films with Various Thicknesses Analyzed By a Transmission Line Equivalent Circuit

In this research, an influence of corrosion products on corrosion behavior of zinc under thin solution films with various thicknesses was studied by electrochemical impedance spectroscopy (EIS). The corrosion products evaluated in this work were formed during periods of exposure corresponding to 1, 3, 6, and 12 months in a natural environment (Japan Weathering Testing Center, Japan) compared with the non-exposed (polished zinc). A solution of 0.2 M NaCl was used as the thin film under conditions varying thickness from 5 to 800 µm. For the films thicker than 50 μm, the solution was directly placed whole electrode cell surface with a micropipette. However, For the films thinner than 25 μm, the solution was prepared by mixing with ethanol on the cell surface. The EIS was carried out to monitor impedance behavior at an open circuit potential (OCP) from the frequency range 10 kHz to 10 mHz. The impedance for the interface of metal and electrolyte (Z total) was obtained by dividing the measured impedance with the two-electrode cell by two. A transmission line model equivalent circuit (TML model) as shown in figure 1 was employed to describe the electrochemical impedance behavior. The EIS bode plots show different behaviors when the thickness of thin solution film changes. From the θ vs. log f plot in exposed zinc, all the shapes show two-time constants, one at high frequencies (HFL) and another at low frequency (LFL) where the phase shift does not exceed -45o. It means current distribution remains non-uniform even in a whole range of frequency in all cases. All electrochemical parameters were successfully obtained from the fitting method by applying the TML equivalent circuit of a metal-thin electrolyte layer interface. The appropriate initial values were optimized before input into the fitting software with the two-time constant. Some parameters of corrosion products such as resistance Rf* and capacitance CPEf* at thickness 800 μm were fixed for all thickness in the same exposure periods, where residual parameters in TML circuit were free. Charge transfer resistance R ct obtained from the fitting results (TML model) was used to study the corrosion behavior. The corrosion current density (i corr) can be calculated from the Stern-Geary equation, k= 13 mV and 4 mV for polished and exposed zinc respectively. For polished zinc, the results of polished zinc show that its corrosion behavior was dependent on a varying of the thin solution films. The i corr tends to increase while the thickness was reduced approximately to 25 µm. This behavior can be described by the diffusion limited current density (i lim) is the important parameter affected by the electrolyte layer thickness in cathodic reaction, i.e., an enhancement of diffusion process of O2 through the water layer. Then, the corrosion behavior is cathodically control. Further reduce of the thickness decreased the i corr due to a lack of amount of water needed for hydration of dissolved metal ions. Therefore, in a transition area, the corrosion rate is anodically control. On the other hand, the i corr of the exposed zinc have the approximate value and the corrosion behavior was independent of the thin solution films for whole thickness range. From these results, they might not be controlled by mass transport (O2 diffusion) but they must be controlled by the charge transfer process for both cathodic and anodic reaction. The cathodic and anodic polarization of the exposed and polished zinc were also measured in 0.2 M NaCl bulk solution. Before measurement, open circuit potential (E ocp) was monitored. The polarization curves show the deviation of Tafel slope for exposed zinc (1, 3, 6 and 12 months) compared to non-exposed one (polished zinc). E ocp of exposed zinc approaches to the positive values. It can be preliminary implied that the charge transfer process of both cathodic and anodic reaction was suppressed by zinc corrosion products which were identified as Zincite (ZnO) and Simonkolleite (Zn5(OH)8Cl2.H2O) whereas the charge transfer process of anodic reaction was more suppressed. Figure 1

Corrosion Behavior of Zinc under Thin Solution Films of Different Thicknesses

Zinc corrosion under 0.2 M NaCl solution films 5–800 μm in thickness was studied by electrochemical impedance spectroscopy (EIS). As-polished and rusted zinc plates obtained by exposure to a natural atmospheric environment for 1, 3, 6, and 12 months were used as working electrodes. The obtained EIS results were analyzed using a transmission line equivalent circuit to determine the charge transfer resistance (Rct), the reciprocal of which is proportional to the corrosion current density. For the as-polished zinc, the corrosion behavior is divided into three regions by the solution film thickness (Xf). In Region I (Xf: 800–200 μm), Rct−1 is independent of Xf and is approximately ten times smaller than that for carbon steel. In Region II (Xf: 200–25 μm), however, Rct−1 increases with decreasing solution thickness down to approximately 25 μm due to an enhancement of the oxygen diffusion (cathodic process) through the solution film. In Region III (Xf < 25 μm), further decreases in thickness reduce Rct−1 because the zinc dissolution (anodic process) is suppressed. In contrast, Rct−1 of the rusted zinc is independent of Xf because the charge transfer process is strongly suppressed by the zinc corrosion products, which were identified as simonkolleite and zinc oxide.

Tortuosity of Battery Electrodes: Validation of Impedance-Derived Values and Critical Comparison with 3D Tomography

Tortuosity values of porous battery electrodes determined using electrochemical impedance spectroscopy in symmetric cells with a non-intercalating electrolyte are typically higher than those values based on numerical analysis of 3D tomographic reconstructions. The electrochemical approach assumes that the electronic resistance in the porous coating is negligible and that the tortuosity of the porous electrode can be calculated from the ionic resistance determined by fitting a transmission line equivalent circuit model to the experimental data. In this work, we validate the assumptions behind the electrochemical approach. First, we experimentally and theoretically investigate the influence of the electronic resistance of the porous electrode on the extracted ionic resistances using a general transmission line model, and provide a convenient method to determine whether the electronic resistance is sufficiently low for the model to be correctly applied. Second, using a macroscopic setup with known tortuosity, we prove that the ionic resistance quantified by the transmission line model indeed yields the true tortuosity of a porous medium. Based on our findings, we analyze the tortuosities of porous electrodes using both X-ray tomography and electrochemical impedance spectroscopy on electrodes from the same coating and conclude that the distribution of the polymeric binder phase, which is not imaged in most tomographic experiments, is a key reason for the underestimated tortuosity values calculated from 3D reconstructions of electrode microstructures.

Parametric evaluation of microstrip log periodic dipole array antenna using transmission line equivalent circuit

This paper presents the design of a Microstrip Log Periodic Dipole Array (MLPDA) antenna for wireless communication in C band. A simplest structure of the edge fed Microstrip Log Periodic Dipole Array is chosen as base design. The parameters of proposed antenna are identified by investigating the effect of variation in geometrical structure on gain and bandwidth. A scale factor (τ) and a spacing factor (σ) are defined accordingly and imposed, in order to create the variations in these parameters. Complexity of parametric variations involved has been observed through change in bandwidth and realized gain of proposed MPLDA. A transmission line equivalent circuit of the proposed MLPDA is developed to give physical insight of the structure and validation. Log periodic nature of the proposed antenna array is verified by plotting input impedance with logarithm of frequency over the specified range. To validate the results, prototype of proposed antenna is realized in the high frequency laboratory and results are verified with few experimentally measured values.

An accurate parasitic parameters extraction method based on FW‐EM for AlGaN/GaN HEMT up to 110 GHz

AbstractIn this paper, an accurate parasitic parameters extraction method based on full wave electromagnetic for 0.1 μm GaN high electron mobility transistors (HEMTs) small‐signal equivalent circuit up to 110 GHz is presented. To describe the distribution effects of HEMTs electrodes at extremely high frequency, a 2‐stage distributed transmission line equivalent circuit model is also presented. To minimize the distribution effects, a shorter gate‐width device, called partial transistor model, is used to extract the second stage (N = 2) parasitic capacitance before extracting the first stage (N = 1) parameters. An AlGaN/GaN HEMT with gate length of 0.1 μm is used for validation, and the experimental results show that good agreement has been achieved between measured and simulated scattering (S) parameters up to 110 GHz.