Coupled Transmission Lines Research Articles

Glide symmetry for mode control and significant suppression of coupling in dual-strip SSPP transmission lines

Glide symmetry, which is one kind of higher symmetry, is introduced in a special type of plasmonic metamaterial, the transmission lines (TLs) of spoof surface plasmon polaritons (SSPPs), in order to control the dispersion characteristics and modal fields of the SSPPs. We show that the glide-symmetric TL presents merged pass bands and mode degeneracy, which lead to broad working bandwidth and extremely low coupling between neighboring TLs. Dual-conductor SSPP TLs with and without glide symmetry are arranged in parallel as two channels with very deep subwavelength separation (e.g., λ0 / 100 at 5 GHz) for the application of integrated circuits and systems. Mutual coupling between the hybrid channels is analyzed using coupled mode theory and characterized in terms of scattering parameters and near-field distributions. We demonstrate theoretically and experimentally that the hybrid TL array obtains significantly more suppressed crosstalk than the uniform array of two nonglide symmetric TLs. Hence, it is concluded that the glide symmetry can be adopted to flexibly design the propagation of SSPPs and benefit the development of highly compact plasmonic circuits.

Effects of electromagnetic interference and crevice on corrosion of natural gas pipelines

Pipeline transportation is the main method of natural gas transportation. The intrinsic safety of natural gas pipelines has always been the focus of attention. During the transportation process, pipelines are affected by many factors. Existing studies have little research on the destruction of natural gas pipelines under the coupling of high-voltage transmission lines with electromagnetic interference and crevice corrosion. However, in actual inspections, it was found that this working condition caused very serious damage to the natural gas pipelines. Therefore, studying the corrosion law of natural gas pipelines under the coupling effect of electromagnetic interference and crevice corrosion can provide a theoretical basis for the safety management of natural gas pipelines. In this paper, through the electromagnetic interference simulation and corrosion test, the corrosion rate of natural gas pipelines under general corrosion, crevice corrosion and coupling of crevice corrosion and electromagnetic interference were analyzed.

Fault location algorithm for partial coupling double-circuit transmission lines

Multi-circuit transmission lines on the same tower have become the inevitable trend of power grid construction, mostly partial coupling mode. Affected by the partial coupling characteristics, the existing fault location methods have large error. Therefore, this paper develops a study about the fault analysis and fault location method for the partial decoupling double-circuit transmission lines. Based on its structure and characteristics, as well as the lines decoupling theory, the interface equations of demarcation point are built. On the basis of the above study, the new fault location algorithm based on time-domain for partial coupling double-circuit transmission lines are presented. Finally, ATP/EMTP is used to construct the model of partial coupling of double-circuit transmission lines. After the overall simulation and verification, it shows that the presented algorithm is accurate.

Features of the implementation of fixed phase shifters on coupled microstrip transmission lines with a stub

Fixed phase shifters with a phase-shifting channel based on coupled transmission lines of class II with a stub have a number of advantages in comparison with previously known structures for similar purposes. However, their practical implementation causes difficulties associated with the topological features of the structure, which, in turn, leads to a deterioration in frequency characteristics. In this regard, a numerical analysis of inhomogeneities in a class II structure with a stub and an assessment of their influence on the frequency characteristics of fixed phase shifters is required. In this work, circuitry and electrodynamic modeling of class II structure elements has been carried out, which showed that the greatest parasitic effect on the frequency characteristics of the phase shifter has a nonzero coupling coefficient of single transmission lines and an inhomogeneity localized at the junction of the short-circuited stub and the output arms of the associated transmission lines. A fixed phase shifter with a phase-shifting channel based on a smoothly stepped structure with a stub has been developed. The presented results of the study of fixed phase shifters based on microstrip coupled transmission lines of class II with a stub can be useful to scientific and technical workers engaged in the development of functional devices for the phase shift of microwave signals.

340-GHz Heterogeneously-Integrated THz Imager With 4°-Beamwidth 16×16 IPD Antenna Array for Lensless Terahertz Imaging Applications

A low-cost and planar heterogeneously-integrated 340-GHz THz imager is proposed for lensless THz imaging applications. The proposed THz imager is composed of a 16×16 antenna array realized in an integrated-passive-device (IPD) technology, an IPD-to-CMOS THz interconnect, and a power detector implemented in a 0.18- μm CMOS technology. The 16×16 IPD antenna array can provide simulated antenna gain of 23.9 dBi, antenna directivity of 30 dB, and half-power beamwidth (HPBW) of 5.6° at 340 GHz. The proposed THz interconnect utilizes a transmission line coupling technique to provide low-loss and broadband signal transition from a CMOS chip to an IPD one while occupying a small chip area. The simulated insertion loss of the THz interconnect is only 1.8 dB at 340 GHz while providing 3-dB bandwidth from 230 to 446 GHz. The power detector exploits the transistor's inherent even-order nonlinearity to rectify the input signal for power detection. The power detector can give simulated voltage responsivity R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> and noise equivalent power (NEP) of 190.2 kV/W and 1.9 nW/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> at 340 GHz, respectively, as the chopping frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mod</sub> is 1 kHz. A nonlinear curve fit technique is proposed to tackle the undesired fluctuation of the measured output voltage due to a standing-wave effect. Experimental results show that the proposed heterogeneously-integrated THz imager can provide measured effective R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> and NEP of 0.967 MV/W and 0.18 nW/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> at 328 GHz, respectively, as f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mod</sub> is 1 kHz. The measured antenna directivity and HPBW can be 30 dB and 4° at 340 GHz, respectively. Such a THz imager with advantages of high antenna directivity and narrow HPBW can be employed to realize a simple, low-cost, and lensless THz imaging system. To the best of the authors' knowledge, the proposed THz imager integrates the highest number of antennas and exhibits the highest antenna directivity and the narrowest HPBW at THz frequencies reported thus far.

Perfect absorption in complex scattering systems with or without hidden symmetries

Wavefront shaping (WFS) schemes for efficient energy deposition in weakly lossy targets is an ongoing challenge for many classical wave technologies relevant to next-generation telecommunications, long-range wireless power transfer, and electromagnetic warfare. In many circumstances these targets are embedded inside complicated enclosures which lack any type of (geometric or hidden) symmetry, such as complex networks, buildings, or vessels, where the hypersensitive nature of multiple interference paths challenges the viability of WFS protocols. We demonstrate the success of a general WFS scheme, based on coherent perfect absorption (CPA) electromagnetic protocols, by utilizing a network of coupled transmission lines with complex connectivity that enforces the absence of geometric symmetries. Our platform allows for control of the local losses inside the network and of the violation of time-reversal symmetry via a magnetic field; thus establishing CPA beyond its initial concept as the time-reversal of a laser cavity, while offering an opportunity for better insight into CPA formation via the implementation of semiclassical tools.

Equivalent circuit of interleaved air-core toroidal transformer derived from analogy with coupled transmission lines

Equivalent circuit of interleaved air-core toroidal transformer derived from analogy with coupled transmission lines

A Preliminary Study on Signal Energy Loss and Crosstalk for Coupled Transmission Lines at 5G Frequency

In this paper, we built models incorporating bent high-speed signal transmission lines and study the quality of the received signal by analyzing the crosstalk between the signal lines. We established different models incorporating regularly bent, fillet, and chamfered corners to investigate their effect on signal crosstalk around 5G frequency. The time domain reflectometry and electromagnetic modes are simulated with finite element methods.

High-Efficiency Microwave Rectifier With Coupled Transmission Line for Low-Power Energy Harvesting and Wireless Power Transmission

In this article, a Schottky diode-based microwave rectifier that employs coupled transmission lines (CTLs) is proposed. CTL is herein used to enhance the voltage amplitude across the Schottky diode with the consequent increase in the rectifier efficiency, especially for low input powers. It is also shown that multiple cascaded CTLs can further enhance the rectifier conversion efficiency, even if this benefit is partially annihilated by the increased insertion loss. Several compact prototypes with single and dual CTLs for 2.45 GHz have been fabricated and measured for different input power levels. Particularly, a single CTL rectifier exhibits RF-to-dc conversion efficiency of 67.7% for an input power of 0 dBm, leading to an improvement of about 3% with respect to other referred rectifiers (with a dc load of 4.47 kQ), while dual CTL rectifier has an outstanding efficiency of 75.3% for an input power of only 5.5 dBm (with a dc load of 1.76 kQ). Passive voltage boost by means of CTLs can be applied to other rectifier circuits as also demonstrated.

Low- and High-Frequency Extrapolation of Band-Limited Frequency Responses to Extract Delay Causal Time Responses

Frequency responses, such as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> parameters, can be utilized to analyze the time-domain characteristics of circuit components and systems using the hybrid time–frequency-domain approach [1]. However, most frequency responses have a limited frequency range and no low-frequency data due to the limitations of the bandwidth of instruments and the computational resource of simulators. Using these frequency responses, the accuracy and delay causality of the extracted time responses cannot be guaranteed, occurring an inaccurate time-domain analysis. Therefore, this article presents a low- and high-frequency extrapolation method to extract the delay causal time responses from the band-limited frequency responses. Unlike previous methods, the proposed extrapolation method can accurately estimate a propagation delay for improving the accuracy of the overall extrapolated frequency response, even if the applied band-limited frequency response has no low-frequency data. Moreover, in this method, the coefficients of both the low- and high-frequency extrapolation functions can be extracted precisely without an intensive iteration. To verify the proposed method, a two-port network using a multisection band-stop filter and a four-port differential channel using coupled transmission lines were designed. In both cases, the proposed method had a higher accuracy than previous methods, such as the delay-based macromodeling scheme and noniterative extrapolation for the high-frequency range. Furthermore, the computational efficiency of the proposed method was also higher than the delay-based macromodeling while maintaining a similar efficiency as with the noniterative extrapolation method.

A Fault Data Based Method for Zero-Sequence Impedance Estimation of Mutually Coupled Transmission Lines

Line impedances estimation is of great importance in power system studies. Different software are used in utilities to calculate line impedances using the line conductor and structure data. The calculated values cannot be reliable due to inaccurate information or change in atmospheric condition. Also, since there is a lack of communication between different departments such as system protection, line construction, etc., a line conductor/structure may be changed while the affected departments are not notified. Most of the impedance estimation methods use phasor measurement units (PMUs) in the protection relays which are connected to protection class current transformers (CTs) that do not provide accurate currents compared to metering class CTs. These methods not only require PMUs in the substations, but also fail to measure zero-sequence voltages and currents due to inadequate zero-sequence components under normal operation. In parallel transmission lines, zero-sequence impedance estimation is even more challenging. This paper introduces a method for estimating the self and mutual zero-sequence impedances for mutually coupled transmission lines using recorded fault data. Extensive simulation and protective relay test results in RSCAD/RTDS indicate that the proposed approach has high accuracy in estimating the self and mutual zero-sequence impedances as well as the fault location in parallel transmission lines.

Optimal Transmission Line Coupling Generation System Design for Rural Electrification

An electric potential appears at floating wires located within a strong electric field. This phenomenon can be used to supply small isolated communities situated close to Extra-High Voltage transmission lines. This non-conventional distributed generation system has been studied for the last years. However, to improve the power generation system the optimal position of the floating wires, number of wires used, bundle radius, and type of wires must be properly identified. This paper presents a mathematical model solved with genetic algorithm to design a collector system with optimized induced voltage and minimized project cost, identifying the optimal reactor used for voltage regulation. The algorithm was applied to design a collector system that can tap-off 100 kW from a 230 kV transmission line. The trade-off between objectives and the Pareto optimal solutions were evidenced via several simulations using the weighting sum approach. These results allowed to identify a final geometry according to a-posteriori designer preferences.

General Conditions to Realize Exceptional Points of Degeneracy in Two Uniform Coupled Transmission Lines

We present the general conditions to realize a fourth order exceptional point of degeneracy (EPD) in two uniform (i.e., invariant along z) lossless and gainless coupled transmission lines (CTLs), namely, a degenerate band edge (DBE). Until now the DBE has been shown only in periodic structures. In contrast, the CTLs considered here are uniform and subdivided into four cases where the two TLs support combinations of forward propagation, backward propagation and evanescent modes (when neglecting the mutual coupling). We demonstrate for the first time that a DBE is supported in uniform CTLs when there is proper coupling between: (i) propagating modes and evanescent modes, (ii) forward and backward propagating modes, or (iii) four evanescent modes (two in each direction). We also show that the loaded quality factor of uniform CTLs exhibiting a fourth order EPD at k=0 is robust to series losses due to the fact that the degenerate modes do not advance in phase. We also provide a microstrip possible implementation of a uniform CTL exhibiting a DBE using periodic series capacitors with very sub-wavelength unit-cell length. Finally, we show an experimental verification of the existence DBE for a microstrip implementation of a CTL supporting coupled propagating and evanescent modes.

A Novel Tri-bandpass Filter Side-coupled Square Ring Based

This work presents the design of a tri-bandpass filter based on the side-coupled square ring structure. The modeling is conceived from the classic approach of coupled transmission lines. The geometry consists of a square structure of electrical length equal to twice the wavelength of the main operating frequency, and the laterally coupled lines through which the power supply occurs. Expressions for the admittance and transformation matrix were obtained based on the impedances and admittances that model the geometry. Analyzis were performed from EM simulations. A prototype was built to validate the modeling and adjusted for operation at 0.78, 1.5 and 2.30 GHz. All results are discussed and commented, and the comparisons between simulated and measured results are coherent and in agreement, thus proving the effectiveness of the applied method.

Distributed Degenerate Band Edge Oscillator

We propose a new class of oscillators by engineering the dispersion of two-coupled periodic waveguides to exhibit a degenerate band edge (DBE). The DBE is an exceptional point of degeneracy (EPD) of order four, i.e., representing the coalescence of four eigenmodes of a waveguide system without loss and gain. We present a distributed DBE oscillator realized in periodic coupled transmission lines with a unique mode selection scheme that leads to a stable single-frequency oscillation, even in the presence of load variation. The DBE oscillator potentially leads to a boost of the efficiency and performance of radio frequency (RF) sources, due to the unique features associated with the EPD concept. This class of oscillators is promising for improving discrete-distributed coherent sources and can be extended to radiating structures to achieve a new class of active integrated antenna arrays.

Novel Low-Cost Power Divider for 5.8 GHz

This paper presents a new capacitive lump-free structure for power dividers using a printed-circuit board, while maintaining size reduction and physical isolation. The conventional lumped capacitors approach has self-resonant problem and cause worse S 22 and isolation at high frequencies. To overcome such technical issues, the coupled-line structures were introduced in the isolation network. After optimizing the distance between output ports and position of the isolation network, tuning the characteristic impedance and electrical length of transmission lines can decide the value of the lump resistor. The first example was designed at 1 GHz, and the resistor in the isolation network was 330 ohm, having 0.2-dB insertion loss and 19% total bandwidth, while maintaining 80-degree distance between split ports and 180-degree total length, providing 21% to 67% size reduction. The second example was designed at 5.8 GHz, which was five times greater than in past research, using an RO4003C substrate while maintaining a 0.24-dB insertion loss, 17% total bandwidth, and 0.06 dB amplitude imbalance, which was only 0.01 dB more than in recent research. Such superior performance is mainly attributed to the coupled transmission lines in the isolation network featuring a capacitive lump-free isolation network. Our data indicate that amplitude imbalance, bandwidth, and miniaturization are superior to any published data.

Adaptive Protection of Partially Coupled Transmission Lines

The mutual coupling effect in parallel transmission lines renders the maloperation of conventional distance relays and makes it more difficult for power system operators to establish a reliable operation of transmission systems. This paper presents an adaptive protection system approach to improve the performance of conventional distance relays in partially coupled transmission lines. The conducted study deals with single-line-to-ground faults and the proposed algorithm is designed for ground distance units. The mutually coupled transmission lines, which are not terminated in same substations, are studied and the impedance estimated by associated distance relays is corrected through revising the level of zero sequence compensation. The compensation term is calculated based on the system equivalent sequential networks and it is substituted in an iterative process for enhancing its accuracy. The proposed approach can offset the fault resistance effect to calculate an accurate fault impedance. The proposed approach lies in the local protection category and utilizes local and very limited remote data for decision making. Simulation results present the adaptive features of the proposed protection scheme. Besides, practical applications of the proposed approach are demonstrated and analyzed through experimental studies by developing a prototype on a MCU (LPC2368_ARM7TDMI) processor.

High Precision CMOS Integrated Delay Chain for X-Ku Band Applications

A high-precision delay chain circuit integrated in a 0.18- $\mu \text{m}$ CMOS technology working in the frequency bandwidth of 8–18 GHz has been designed and tested. The designed delay control integrated circuit with 5-bit delay control provides a maximum delay of 125 ps and has a delay resolution of 3.9 ps. Measured delay error of the fabricated chip is less than 9.3%, making it a considerably accurate delay control circuit. Low delay-error performance has resulted from incorporating a novel delay cell in this delay chain circuit. This newly proposed delay cell is a lumped-element coupled transmission line loaded with a second-order all-pass network (APN). The APN-loaded coupled line delay cell has larger delay-bandwidth product and is less prone to parasitic capacitances of inductor elements compared with conventional passive second-order APN delay cells. The fabricated chip utilizing the novel delay cell occupies an area of $0.9\times3.6$ mm2 and consumes 115.5- and 13.5-mW dc power from a 3.3-V voltage supply in its high- and low-power modes, respectively.

Mobile Teaching and Learning of Coupled-Line Structures: The multiple-1D coupled-line finite-difference time-domain method

In this article, we present mobile teaching and learning of coupled-line structures using the multiple-1D coupled-line finite-difference time-domain (M1D CL-FDTD) method. The formulation of the M1D CL-FDTD method applicable for CL structures is provided. The method bypasses the more computationally intensive full-wave 3D method, and it is well suited for implementation on mobile devices. Several mobile apps are developed to provide interactive visualization of electromagnetic (EM) wave propagation in CL structures. These visualizations allow the underlying resonating and coupling mechanisms to be elucidated clearly and improve students' understanding of CL theories. Mobile teaching and learning of various CL structures, including coupled transmission lines, CL bandpass filters, directional couplers, and branch-line couplers, are demonstrated and discussed.

Coupled Lines for Wearable Power Dividers: Coupled Transmission-Line Sections for Power Dividers in Wearable and Flexible RF Electronics

In 2013, the Global Standards Initiatives on Internet of Things (IoT) defined the IoT as global infrastructure for the information society, enabling advanced services by interconnecting things based on existing and evolving interoperable information and communication technologies, with the term thing described as an object in the information world that is capable of being indentified and integrated into communication networks. Things in the IoT sense can, therefore, refer to a wide variety of devices for media, environmental monitoring, infrastructure management, manufacturing, energy management, medicine and health care, building and home automation, transportation, metropolitan-scale deployments, and consumer applications that demand accurate and reliable methods to sense changes, even in extremely rugged environments [1].