Simple Transmission Line Research Articles

A novel compact directional coupler with high directivity based on CRLH transmission lines

Designing and fabricating a directional coupler with composite right/left-hand (CRLH) transmission lines with a coupling level of 15 dB is presented in this paper. Compared to conventional couplers, this asymmetric structure has achieved this coupling level compared to the simple transmission line. This structure is comprised of interdigital capacitors and short connection stubs. The distance between two coupled lines is equal to 0.4 mm, and the stubs are spirally designed to compress the structure. The subs’ length is approximately equal to λ/4, and the impedance of the ports is equal to 50 Ω. After designing and simulating, the coupler was fabricated and measured. The directional coupler at the frequency of 1.9 GHz has an isolation level of 44 dB and a directivity of 67.1 dB. Overall, construction and simulation results are in good agreement.

Layer by Layer: Improved Tortuosity in High Loading Aqueous NMC811 Electrodes

Thick electrode production is a key enabler for realizing high energy density Lithium-ion batteries. Therefore, the investigation of tortuosity as a crucial limiting parameter was conducted in this work. A thickness threshold (>150 μm) for a drastic increase in tortuosity for aqueous processed LiNi0.8Mn0.1Co0.1O2 (NMC811) electrodes was determined. Symmetrical cells, under blocking conditions, were analyzed via electrochemical impedance spectroscopy. To counteract this phenomenon, multi-layer coated electrodes with varying binder concentrations were investigated. This novel coating method, combined with the reduction of binder material, leads to a tortuosity decrease of more than 80%, when compared to high-loading electrodes (>8.5 mAhcm−2) coated with the conventional doctor-blade technique. Additionally, a simplified transmission line model is opposed to a linear fitting method for analyzing the impedance data.

Design and Fabrication of Stretchable Microwave Transmission Lines Based on a Quasi-Microstrip Structure.

Radio frequency (RF) electronics are vital components of stretchable electronics that require wireless capabilities, ranging from skin-interfaced wearable systems to implantable devices to soft robotics. One of the key challenges in stretchable electronics is achieving near-lossless transmission line technology that can carry high-frequency electrical signals between various RF components. Almost all existing stretchable interconnection strategies only demonstrate direct current or low-frequency electrical properties, limiting their use in high frequencies, especially in the MHz to GHz range. Here, we describe the design and fabrication of a simple stretchable RF transmission line strategy that integrates a quasi-microstrip structure into a stretchable serpentine microscale interconnection. We show the effects of quasi-microstrip structural dimensions on the RF performance based on detailed quantitative analysis and experimentally demonstrate the optimized device capable of carrying RF signals with frequencies of up to 40 GHz with near-lossless characteristics. To show the potential application of our transmission line in stretchable microwave electronics, we designed a single-stage power amplifier system with a gain of 9.8 dB at 9 GHz that fully utilizes our quasi-microstrip transmission line technology.

Implementation of a Wideband Microwave Filter Design with Dual Electromagnetic Interference (EMI) Mitigation for Modern Wireless Communication Systems with Low Insertion Loss and High Selectivity.

By leveraging the advantages of the uniform transmission line, this manuscript presents a broadband high-selectivity filter range starting from 2.5 GHz to 16.8 GHz, utilizing a simple uniform transmission line structure loaded with three-quarter-wavelength stubs. The proposed UWB filter is studied using the ABCD network parameter method. After that, a shorted T-shaped stub-loaded resonator is coupled with the transmission line of the UWB filter to obtain dual-notch features at 4.4 GHz (for long distance wireless ISPs (WISPs), 4G/5G operator for LTE backhaul) and 7.5 GHz (for X-band downlink communication). The overall footprint is specified as 22.5 mm × 12 mm or 1.12 λg × 0.6 λg, where λg represents the wavelength at the central frequency. The operating principle of such a filter is explained, and its controllable broadband response, as well as controllable stopband frequencies, are optimized to show some of the attractive features of the new scheme, such as a super wideband response of about a 148.18% fractional bandwidth; an out-of-band performance up to 25 GHz; five single-resonator transmission poles filtering behaviour at different frequencies, with highly reduced radiation losses greater than 10 dB; a simple topology; a flat group delay; a low insertion loss of 0.4 dB; and high selectivity. Additionally, the filter is fabricated and evaluated, and the results show a good match for experimental validation purposes.

Amplitude‐Controlled Electromagnetic Pulse Switching Using Waveguide Junctions for High‐Speed Computing Processes

Performing computational tasks with wave‐based devices is becoming a groundbreaking paradigm that can open new opportunities for the next generation of efficient analogue/digital computing systems. Decision‐making process for switching and routing of signals is fundamental for computing as it enables the transfer of information from one to many (or single) blocks within a system. Herein, a technique is proposed for the design of pulse‐based switching devices for the computing of fundamental decision‐making processes. Information is encoded from multiple channels as transverse electromagnetic (TEM) pulses of varying amplitudes and polarities propagating through interconnected parallel plate waveguides modeled as simple transmission lines. An in‐depth description of the technique is presented showing how switching and routing of information can be engineered by exploiting the linear splitting and superposition of multiple pulses traveling through waveguide junctions. To demonstrate the potential of the technique, two devices are developed: a comparator which can calculate the largest value between two real‐valued numbers and a pulse director which exploits the reciprocity of waveguide junctions to create a similar yet different performance of a traditional AND gate (emulating its performance via the analogue linear system). These findings may open new pathways for high‐speed electromagnetic pulse‐based computing systems.

A New Design Approach for a Compact Microstrip Diplexer with Good Passband Characteristics

This paper presents an efficient theoretical design approach of a very compact microstrip diplexer for modern wireless communication system applications. The proposed basic resonator is made of coupled lines, simple transmission line and a shunt stub. The coupled lines and transmission line make a U-shape resonator while the shunt stub is loaded inside the U-shape cell to save the size significantly, where the overall size of the presented diplexer is only 0.008 λg2 . The configuration of this resonator is analyzed to increase intuitive understanding of the structure and easier optimization. The first and second resonance frequencies are f o1 = 895 MHz and f o2 = 2.2 GHz. Both channels have good properties so that the best simulated insertion loss at the first channel (0.075 dB) and the best simulated common port return losses at both channels (40.3 dB and 31.77 dB) are achieved. The presented diplexer can suppress the harmonics acceptably up to 3 GHz (3.3 fo1 ). Another feature is having 31% fractional bandwidth at the first channel.

A Low-Profile Compact Meander Line Telemetry Antenna with Low SAR for Medical Applications

A low-profile Compact Meander Line Telemetry Antenna (CMLTA) operating at 402.5 MHz for the Medical Implant Communication System (MICS) band medical applications is introduced. The proposed antenna focuses specifically on pacemaker telemetry applications. The meander line technique with an open loop configuration and simple transmission line feeding mechanism has been used for achieving the compact design. Based on the theory of surface current distribution, the proposed technique provides the opportunity to increase the electrical dimensions while decreasing the physical dimensions of the antenna. Further design optimization is carried out to optimize the overall antenna size to a maximum volume of 4080 mm3. By introducing CMLTA, the size of the antenna is reduced by 79% as compared to the previous work. The proposed antenna demonstrated satisfactory performance with 10 dB bandwidth of 6.17%, a maximum gain of -22 dBi and an EIRP of -25.28 dBi. The analysis of Specific Absorption Rate under premise use of 1 W input power provided the maximum 1 g and averaged 10 g SAR of 74.7 W/kg and 17.7 W/kg, respectively, demonstrating a satisfactory level according to the IEEE standard safety guidelines. Fabrication and measurements are carried out where measured results are found to be in good agreement with the simulated results. With the optimized dimensions, satisfactory gain, EIRP, and SAR performance, the proposed CMLTA is deemed suitable for pacemaker telemetry applications for effective communication.

HilbertNet: A Probabilistic Machine Learning Framework for Frequency Response Extrapolation of Electromagnetic Structures

In this article, we propose a probabilistic machine learning framework for extrapolating the frequency response of distributed physical circuits. For the structures where there is hidden dependency between higher and lower frequency features, we propose a method to extrapolate the response while providing confidence intervals harnessing Bayesian recurrent neural networks (RNN) thereby avoiding extensive simulations and saving computational time. To address complex-valued impedance, Hilbert transform is used to relate the real and imaginary parts where a Hilbert-based RNN architecture is proposed called Hilbert Net to extrapolate the frequency response. We apply the technique to four applications: 1) A simple microstrip transmission line circuit for proof of concept, 2) coupled waveguide filter operating in D-band comparing with measured results, 3) fifth-order interdigital bandpass filter for 28 GHz band, and 4) complex stack-up power delivery network (PDN) having a sharply changing response to test the framework limits. Results show that our architecture performs accurate extrapolation with a normalized mean square error of 0.008 squared with 95% confidence for a typical PDN. Using probabilistic networks, we achieve a tight confidence bound on our results. Furthermore, the reliability of Hilbert Net is assessed as to how far the response can be extrapolated.

Design and Analysis of a Metamaterial-Inspired Miniaturized Quadband Antenna

A metamaterial-inspired miniaturized quadband antenna is designed and discussed with a transmission line model to study the theory of miniaturization and multiband in this paper. A conventional printed monopole antenna is assumed as a primary antenna and then surrounded by an array of 4 × 2 interdigital LHMs. The proposed antenna has a compact size of 36 mm × 24 mm × 1 mm , and operates at 2.40–2.55 GHz, 3.02–3.38 GHz, 5.04–5.52 GHz, and 7.08–7.38 GHz. Good gain and omnidirectional radiation patterns are observed in simulations and measurements. A simplified transmission line modal was established to study the reasons for miniaturization and multiband that were brought about by the LHM array. Related results verified the theoretical analysis and indicated that the proposed antenna is a good candidate for wireless communication applications.

A Platinum Micro-Reference Electrode for Impedance Measurements in a PEM Water Electrolysis Cell

We present a platinum wire micro-reference electrode (Pt-WRE) suitable for recording individual electrochemical impedance spectra of both the anode and the cathode in a proton exchange membrane water electrolyzer (PEM-WE). For this purpose, a thin, insulated Pt-wire reference electrode (Pt-WRE) was laminated centrally between two 50 μm Nafion® membranes, whereby the potential of the Pt-WRE is determined by the ratio of the local H2 and O2 permeation fluxes at the tip of the Pt-WRE. Impedance analysis with the Pt-WRE allows determination of the proton sheet resistance of the anode, the anode catalyst layer capacitance, and the high-frequency resistance (HFR) of both electrodes individually, using a simple transmission-line model. This new diagnostic tool was used to analyze performance degradation during an accelerated stress test (AST), where low and high current densities were alternated with idle periods without current (i.e., at open circuit voltage (OCV)), mimicking the fluctuating operation of a PEM-WE with renewable energy. Our analysis revealed that the increasing HFR that was observed over the course of the OCV-AST, which is the main cause for the observed performance decrease, can unequivocally be assigned to an increasing contact resistance between the anode electrode and the porous transport layer.

Polarization twist reflector antenna — A systematic design approach

In this paper, we present an easy and systematic design approach to realize a polarization twist reflector antenna. Detail description has been provided on how to design a transreflector antenna and its constituents including the transreflector, the polarization twist-reflector, and the feed horn. Simple relations for calculation of reflection coefficients of the trans-reflector and the twist- reflector with plane wave incidence have been considered. Simple transmission line model based analyses have been presented. As it does not involve any integral equation or summation of series of some functions, the final results can be obtained within few seconds with the minimum computational resource requirement. Conductive gratings have been conceived for both trans-reflector and twist-reflector. Their performances have been optimized individually in terms of their grating parameters. A linearly polarized pyramidal horn located at the prime focus of the transreflector has been used for the excitation. A prototype of the complete antenna has been designed at Ka-band, fabricated and experimentally measured. 19% impedance bandwidth with average gain of ≈32.3 dBi has been demonstrated.

Shielded open-circuited probe for in-situ measurements of soil permittivity in Very high frequency (VHF) and Ultra high frequency (UHF) bands

In this paper, the shielded open-circuited probe operating in the wide frequency range from 75MHz to 2GHz is proposed. The probe is made of an SubMiniature version A (SMA) flange connector. The central rod of the SMA connector emerges from a coaxial transition in the flange and shielded by four rods. The robe design allows us to calculate of the probe reflection coefficient S11 used simple analytical transmission line model (TEM wave mode), the parameters of which were calibrated on a set of substances with a known frequency spectrum of permittivity. The refractive index (RI) and normalized attenuation coefficient (NAC) retrieval technique is based on solving the inverse problem of minimizing the residual norm between measured and calculated frequency spectra of reflection coefficient S11. After calibration, the root-mean-square error (determination coefficient) between the measured and calculated module and phase of the reflection coefficient S11 for the sets of calibration media air, distilled water, butanol, pure ice, water solution with NaCl of salinity of 8.9% do not exceed 0.26dB (0.995) and 0.03 rad (0.999), respectively, in the frequency range from 75MHz to 2GHz. The root-mean-square error (determination coefficient) between the measured RI and NAC spectra for four soil cover samples (variation of the clay fraction from 10.5 g/g to 47.6 g/g) using the proposed probe and a precision coaxial cell not exceeds 0.109 (0.993) and 0.057 (0.986), respectively, in the frequency range from 75 MHz to 2 GHz. As a result, it is experimentally shown that RI и NAC can be measured by the proposed non-precision probe with an error comparable to the precision coaxial cell.

Methods—Understanding Porous Electrode Impedance and the Implications for the Impedance Analysis of Li-Ion Battery Electrodes

Two of the main factors influencing the performance of Li-ion battery (LIB) electrodes are the kinetic losses due to the charge transfer resistance of the active material () and the ionic transport resistance in the electrolyte phase within the electrode pores (). Seeking to increase the energy density of LIBs, ever higher active material loadings are applied, resulting in thicker electrodes for which becomes dominant. As electrochemical impedance spectroscopy is commonly used to quantify of electrodes, understanding the impact of on the impedance response of thick electrodes is crucial. By use of a simplified transmission line model (TLM), we simulate the impedance response of electrodes as a function of electrode loading. This will be compared to the impedance of graphite anodes (obtained using a micro-reference electrode), demonstrating that their impedance response varies from purely kinetically limited at 0.6 mAh cm−2 to purely transport limited at 7.5 mAh cm−2. We then introduce a simple method with which and can be determined from the electrode impedance, even under transport limited conditions. Finally, we show how the initially homogenous ionic current distribution across porous electrodes under kinetically limited conditions becomes severely inhomogeneous under transport limited conditions.

확장된 백오프 출력에서 고효율 동작을 위한 최적화된 대칭 이단 도허티 전력 증폭기 설계

This article presents a symmetric two-stage Doherty power amplifier (DPA) for the extended output power back-off level, which can be attained even with a reduced circuit size by changing the output impedance of the peaking amplifier to be inductive without the offset line. The ABCD matrix is employed to design the output matching network of the peaking amplifier with a simple transmission line. Consequently, we can reduce the design complexity by applying the same circuit to the carrier amplifier as the DPA is symmetric. To deal with reduced output power of the class-C peaking amplifier, a two-stage DPA structure was applied. The power amplifier exhibited a drain efficiency (DE) of 63.5 %, and a power added efficiency (PAE) of 50.6 % at 7.5 dB output backoff was obtained using the 3.5 GHz pulsed continuous wave (CW) signal. Furthermore, a DE of 53.3 %, a PAE of 43.2 % and a power gain of 18 dB were obtained at the power level of 41 dBm using a 20 MHz LTE signal with a peak-to-average power ratio of 7.5 dB.

Improved Transmission Line Parameter Calculation Through TCAD Process Modeling for Superconductor Integrated Circuit Interconnects

The Florida Object-Oriented Device, Process and Reliability Simulator (FLOOXS) technology computer-aided design process modeling tools developed at the University of Florida have been adapted under the Intelligence Advanced Research Projects Activity SuperTools program to support the MIT Lincoln Laboratory SFQ5ee fabrication process. We use FLOOXS to build meshed models of passive transmission lines from superconductor integrated circuit layouts. We have previously developed a numerical solver that extracts transmission line parameters from the meshed model. In this work, we convert a layout slice to FLOOXS inputs, generate two-dimensional meshes of cross-sectional geometries from simulated process steps, and then extract the transmission line parameters from the meshes. Results are shown compared against the results for simplified transmission lines that do not utilize process modeling. The results confirm that process modeling alters the extracted parameter values and suggest that process modeling will become more important as cell density of superconducting electronics increases. We conclude with a discussion on the necessity of process modeling for high-quality parameter extraction.

Ka-Band Passive Phased-Array Antenna With Substrate Integrated Waveguide Tunable Phase Shifter

A low-cost and low-profile Ka-band passive phased-array antenna (PAA) using continuously tunable substrate-integrated waveguide (SIW) phase shifter is presented in this article. The phase shifting mechanism is based on perturbing the electric field of the slotted SIW (SSIW) line by putting a high dielectric constant slab over the slot of SIW. A systematic approach based on a simple transmission line (TL) circuit model which can support different modes is developed as a fast method for design optimization. It provides insightful physical understanding of the operating mechanism of the proposed phase shifter. In addition, a fully verified TL model of the 1 x 4 SIW PAA is presented and used to predict and optimize the overall reflection coefficients and radiation patterns at different scanning angles. The TL circuit model is verified by full-wave simulations. As a design example, a 1 x 4 SIW-based phased-array is designed, fabricated, and measured to validate phase shifter performance and capabilities. The prototype exhibits a continuous beam scanning range from -20° to +20° covering the whole operating band of 29-31 GHz.

Calculating the Interface Flow Limits for the Expanded Use of High-Voltage Direct Current in Power Systems

Although loads are increasingly becoming concentrated in metropolitan areas, power generation has decreased in metropolitan areas and increased in nonmetropolitan areas; hence, power transmission must occur through interface lines. To achieve this, additional transmission lines must be secured because the existing interface lines have reached their large-scale power transmission limits. The Korea Electric Power Corporation has installed many high-voltage direct current lines, thereby impacting the determination of interface power flow limits. These serve as the basis for system operations. However, knowledge of operating high-voltage direct current lines as a simple transmission line in a single power system is lacking. The effects of high-voltage direct current and its related parameters for interface flow limit analysis remain unclear. Furthermore, whether high-voltage direct current should be included in the selection of the interface lines that serve as the basis for interface flow remains unclear. In addition, whether the high-voltage direct current line faults should be included in the contingency list for determining the interface flow limits has not been considered. Additionally, it has not been determined whether to operate the DC tap when performing the simulation This study addresses these issues and determines the conditions that are necessary for determining the interface flow limits when a high-voltage direct current transmission facility has been installed in a land power system. The results conclude how to reflect the above conditions reasonably when performing the interface flow limit analysis on a system that includes the HVDC lines.

A Model-Based DC Fault Location Scheme for Multi-Terminal MMC-HVDC Systems Using a Simplified Transmission Line Representation

Accurately determining the location of DC pole-to-pole short-circuit faults in modular multilevel converter (MMC) based multi-terminal HVDC (MTDC) systems is key issue in ensuring fast power recovery. This paper proposes an effective DC fault location scheme for the MMC-MTDC that uses an estimated R-L representation of the transmission lines. By using the measured voltage and current data from both ends of the faulted DC line, the proposed fault location formulas can calculate the location of the fault with high accuracy. The simplified R-L representation greatly reduces the computation burden of the fault detection algorithm. Electromagnetic transient (EMT) simulations of a four-terminal MMC-MTDC system on PSCAD/EMTDC are used to confirm the effectiveness of the proposed approach. The results verify that the proposed scheme is robust and almost not affected by the transmitted power or the fault resistance.

Simplifying Through-Forest Propagation Modelling

Propagation analysis and modeling is critical for radio systems design, but remains a challenge for most through-vegetation situations, including forests. Transmission through such inhomogeneous mixed media is complicated by the many different propagation mechanisms and the complexity of the randomness. This means that accurate, purely physics-based analysis is unlikely to be practical (conveniently computed), and similarly, that practical, purely random modeling is unlikely to be accurate. Through-vegetation propagation models, including the standard radiative energy transfer (RET), are not very accurate in the sense that the uncertainty can be tens of dB, and this seems to be an accepted limitation for vegetation. A simpler propagation model, which maintains or improves accuracy, but keeps a reasonable association with the physics, would be insightful. This paper discusses such a model. It comprises two parallel transmission mechanisms: direct transmission through a succession of trees, which is modeled by a simple linear transmission line; and transmission across the forest top, which is modeled by simplified multiple-edge diffraction. The model is examined using recently-published experiments over a long path-length. It is demonstrated that this two-mechanism model can provide an accurate fit to the dual-slope profile of through-forest propagation over a long distance which is not possible with the RET model.

Two-Way Tunable Phase Shifter With Arbitrary Phase Shift Ratio at Two Different Frequencies

This article presents a new class of tunable passive two-way phase shifters, which can provide an arbitrary phase shift ratio at two different transmit and receive frequencies ( $f_{T}$ and $f_{R}$ ) simultaneously. The proposed phase shifter uses one control element to control both paths. This architecture consists of two transmit and receive paths and a high dielectric constant slab over the paths. By properly setting the length ratio between transmit and receive lines under the dielectric slab, the proposed phase shifters can realize any arbitrary phase shift ratio. For fast and accurate modeling of the proposed phase shifter, a simple Transmission Line (TL) circuit model is presented in this article and verified by full-wave simulations and measurement. The model can be used for calculating the reflection coefficient and phase shift. In order to prove the concept, two phase shifters, one with equal phase shift ( $\Phi _{T}/\Phi _{R}=1$ ) and the other with the phase shift is equal to the ratio transmit frequency and receive frequency ( $\Phi _{T}/\Phi _{R}=f_{T}/f_{R}$ ), are designed, fabricated, and measured. All results show very good agreement between the proposed TL model, the full-wave solver, and measurement results. This type of phase shifter can be used for many beam-forming antenna systems, such as interleaved arrays, full-duplex arrays, and multiband arrays.