Length Of Transmission Line Research Articles

A Novel Fully Reconfigurable Non Foster Capacitance Using Distributed Negative Group Delay Networks

A novel reconfigurable non-Foster capacitance (NFC) using negative group delay (NGD) circuit is presented in this paper. The NGD circuit is based on a multi-order distributed amplifier which is used to achieve both NGD performance and gain compensation. By introducing shunt and series varactors next to trans-conductance transistors in the amplifier, the characteristic impedance, and electric length of transmission lines in the distributed amplifier can be flexibly tuned. As a result, the gain, phase shift, and negative group delay value of the proposed NGD circuit can be easily controlled as desired, and therefore, the scattering parameters S 21 can be adjusted to match with an ideal NFC, resulting in reconfigurable non-Foster capacitance. The working frequency ranges, equivalent negative capacitance value, and connection modes of the NFC be fully reconfigured by appropriately controlling the voltages applied to the varactors. Both simulation and measurement results were given, which agree well with each other. The experimental results show that the NFC value can be tuned from -1.1 to -2.5pF with 1 GHz center frequency and the working frequency can be tuned from 0.7 to 0.8 GHz with -10 pF shunt NFC.

Phase Reconfigurable Microwave Power Divider

A reconfigurable power divider (PD) that can operate either in an in-phase mode or out-of-phase mode is presented. To that end, the novel concept of using tunable phase shifter, which is a reflection-type loaded coupled lines, to emulate an effective variable length transmission line (TL) is utilized. The proposed PD uses a quarter-wavelength TL, a $100~{\Omega }$ isolation resistor and two tunable phase shifters. The presented theoretical analysis shows that by properly selecting the parameters of the phase shifter, it can be used to approximate the performance of variable length TL. To validate the design, a prototype of dimensions 50 mm ${\times }$ 25 mm is built, using Rogers RO3010 substrate, and tested. The results indicate that the device can operate as an in-phase and out-of-phase by using suitable biasing voltages. Across the band 0.9–1.1 GHz, the device has more than 12 dB return loss at all the ports and more than 15 dB isolation between the two output ports with less than 5° phase deviation for both of the in-phase and out-of-phase states.

Analysis of the High-Frequency Response of Thin Wires Irradiated by Electromagnetic Waves Through Tikhonov Regularization Technique

The formula for analyzing the response characteristics of the induced current on a transmission line (TL) excited by high-frequency electromagnetic (EM) waves is a mixed integral-differential equation. The integral part is the Fredholm integral equation of the first kind with serious ill-posedness, which causes difficulty in solving it stably. The regularization technique is a useful method for the analysis of the ill-posed problems. Therefore, in this paper, a method based on the Tikhonov regularization technique is proposed to analyze the high-frequency electromagnetic response of a finite length TL illuminated by external EM waves. The integral operator is discretized by the Simpson formula. The validity and correctness of the proposed method have been verified by numerical examples and the applicability of the proposed method at different errors has been analyzed via the TL with different height.

Approximate Analysis Method for Frequency-Selective Surface Based on Kirchhoff-Type Circuit

A novel approximate method based on the Kirchhoff-type circuit for frequency-selective surface (FSS) analysis is presented in this paper. Instead of splitting up the array element and solving a higher order impedance/admittance matrix equation in the periodic moment method, the equivalent transmission line method is adopted to obtain analytical solutions of the normalized receiving current (or magnetic current) distribution for pattern functions. The impedance/admittance elements and transmission coefficients can then be analytically calculated using Munk’s scheme. The proposed method can be applied to generic FSS elements composed of relatively narrow straight slots/strips. The revision scheme of the equivalent transmission line lengths is proposed to account for discontinuity effects at corners of the element. The transmission coefficients of the six biplanar symmetric hybrid radomes are computed to verify the accuracy and efficiency of the presented method.

Enhanced broadband common‐mode filter based on periodic electromagnetic bandgap structures

AbstractIn this article, we present an enhanced broadband common‐mode (CM) noise filter based on periodic electromagnetic bandgap (EBG) structures with transmission lines. The unit‐cell of the proposed filter is composed of a mushroom‐like resonator and transmission lines. We developed a lumped circuit model with transmission lines to enable analysis of the unit‐cell using the Bloch‐Floquet theorem. The dispersion relations derived from the Bloch‐Floquet theorem have CM suppression characteristics with respect to various circuit parameters. Although optimizing the period of the EBGs by the transmission line length widens the CM noise stop band, the impedance mismatching between the EBGs and the transmission lines causes differential‐mode (DM) insertion loss. We solved this problem by adjusting the characteristic impedance of the DM signals on the EBG. We then built a prototype of the proposed CM noise filter and measured its performance. The frequency range of the 20‐dB CM noise stop band was measured to be 5.3‐9.74 GHz. The DM insertion loss was measured to be < 3 dB from DC to 10 GHz.

A study on multi frequency operation of RF transmission system for EC H&CD system

To study the performance of multi frequency operation of transmission lines for electron cyclotron heating and current drive (EC H&CD) systems, the performance of a transmission line (TL) with 104 GHz/137 GHz/170 GHz operation was evaluated using a multi frequency gyrotron. The TL test stand for multi frequency high-power operation was composed from corrugated waveguides with 63.5 mm inner diameter and TL components, such as miter bends. The coupling efficiency of gyrotron power into the TL inlet, mode purity at the TL end, and power transmission efficiency were measured for three frequency operations. The transmission efficiency of the 40 m length TL remained at 94%–95% for three frequencies and that of the MOU varied because of the quasi-optical design in the MOU. The mode conversion in TL was found to be less than 2% for three frequencies. These results indicate that the TL using corrugated waveguide can deliver radio frequency power from the gyrotron to the launcher with similar performance expected in single frequency operation in ITER.

Impact of distribution and transmission investment costs of district heating systems on district heating potential

In this paper, we use a heat density map (HDM) and a plot ratio map to propose a GIS-based method for determining potential DH areas with specific focus on district heating (DH) grid costs. The DH areas are determined via performing sensitivity analyses on the HDM under consideration of predefined upper bound of the average distribution costs. The approach additionally allows for estimation of length and diameter of transmission lines and their associated costs. The outputs are GIS layers that illustrate areas that are economically viable for construction of DH as well as the cost-minimal transmission lines connecting these regions to each other. The impacts of key input parameters like grid costs ceiling and market share on potential and on expansion and extension of the DH systems were studied for the case study of Vienna. The results showed that the increase of DH market share in DH areas under a certain grid cost ceiling significantly reduce average grid costs. In addition, it was revealed that the expansion of DH system without increasing the market share in the DH areas does not effectively increase the share of DH from the total heat demand and leads to higher average grid costs. These results call for policy interventions like spatial heat planning, zoning and implementation of district heating priority areas.

A Multiline Multimaterial Calibration Method for Liquid Characterization

A multiline and multimaterial calibration method is proposed, which is aimed at replacing state-of-the-art two-tier microwave calibration techniques in liquid characterization process. The technique combines a general “line–line” trace method and an equivalent impedance algorithm, which enables to use unknown materials loaded on various lengths of transmission lines in the calibration standards. The validation measurements are performed on coplanar waveguide structures due to the convenient fabrication and easy integration with polymers. Measurement comparison with the previous calibration approach verifies its capability in high-frequency applications.

Improved broadband (75–110 GHz) radio frequency characteristics of MEMS shunt switches on quartz substrate

This paper presents improved W-band (75–110 GHz) radio frequency characteristics of micro-electromechanical switches in T and π-matched configurations. The switch structures consist of Au metallic bridge (s) suspended over the coplanar waveguide (CPW) signal line drawn on quartz substrate. Here, a high impedance transmission line is introduced on both the sides of the bridge structure to reduce the return loss. To further tune up the broadband RF response the bridge width (40–80 µm) as well the dielectric thickness (0.15–0.18 µm) are varied. At optimum condition (bridge width: 60 µm; dielectric thickness: 0.18 µm), the T-matched RFMEMS switch structure exhibits return loss better than − 20 dB; insertion loss ~ − 0.2 dB and isolation better than − 30 dB in full W-band frequency range. In π-match configuration, a short section of high impedance transmission line is being introduced between two switch structures for impedance matching. RF parameters of the π-matched shunt switch structure are studied as a function of width (10–40 µm) and length (30–180 µm) of the high impedance transmission line. At optimum condition (line width: 30 µm; length: 130 µm), the π-matched switch structure exhibits return loss: better than − 15 dB; insertion loss: better than − 0.5 dB; and isolation: better than − 45 dB over the entire W-band. From the equivalent circuit modeling, the equivalent inductance, capacitance and resistance values for the optimized switch structures are also reported.

Compact Beam-Steerable Antenna Array With Two Passive Parasitic Elements for 5G Mobile Terminals at 28 GHz

A compact beam-steerable antenna array is proposed for 28 GHz mobile terminals. The proposed array consists of one active element and two passive parasitic elements. Two switches are utilized in the design instead of phase shifters. Each parasitic element can be terminated with short-circuited transmission lines of different lengths via one switch. By controlling the two switches, different reactive impedance is loaded on two parasitic elements. The radiation pattern of the active element can be scattered into different directions by two parasitic elements. The switching loss is studied, where two switches with 2.8 dB loss cause less than 1.82 dB loss for the whole array. The small array locations on the chassis are also investigated. The designed array is smaller than 0.81 wavelength, and covers the band of 28–29 GHz with the scan angle ≥±90°. By placing two arrays on each long chassis edge, 360° beam steering can be realized. Surface currents on the chassis are efficiently excited to achieve high gain with the small array. Measurements are carried out and align well with simulations. In practical applications, several small arrays can be implemented on the metal back cover and around a cellphone to combat users’ mobility.

Mechanism and Mitigation of Power Fluctuation Overvoltage for Ultrahigh Voltage Half-Wave Length Transmission System

A new type of overvoltage phenomenon in half-wave length transmission line (HWLL) is caused by power fluctuation (PF). This paper defines this phenomenon as PF overvoltage (PFO), which belongs to the temporary overvoltage category. The amplitude of PFO is generally high, the duration time is long, and the coverage on HWLLs is wide in the case of single-phase transient fault, when the transmission power is large. This will pose a new problem for ultrahigh voltage (UHV) half-wave length ac transmission (HWACT). First, we analyze the unique transmission characteristics of HWLLs with incident and reflected wave theory. Next, according to the application scenario of HWACT in China, we construct a plant-to-grid UHV half-wave length transmission system. Then, based on a large number of electromagnetic transient simulations on the system using electromagnetic program, we obtain the PF characteristics of the UHV HWLL. Furthermore, the mechanism and characteristics of PFO are described by the characteristics of transmission and PF. Finally, we propose the mitigation measures of PFO for UHV HWLL, which include configuring metal oxide arresters differentially along HWLLs, closing high-speed grounding switches during the fault period, generator tripping after a fault, and shortening the reclosing time.

Analysis and mitigation of low-frequency resonance in a long-distance UHVDC ±1100 kV system

Low-frequency resonance may seriously threaten the stable operation of a long-distance ultra-high-voltage-direct-current (UHVDC) system. In this paper, the impedance model of long-distance UHVDC systems was analyzed for various disturbances. For different disturbances, the positions of voltage sources in the simulated DC loop are different. Taking the first ±1100-kV DC power transmission project with a length of 2688km as an example, the frequency characteristics of the DC-loop impedance were studied using the PSCAD/EMTDC simulation platform. The effects of various operating modes and the firing angle of the converters on impedance–frequency characteristics of the DC loop were discussed. The effect of the length of DC transmission lines on the DC-loop resonant frequency was studied. The distance is the most important factor determining the system low-frequency resonance. Faults in an AC grid, such as phase-to-phase short-circuit and single-phase faults, are shown to produce 50-Hz positive sequence harmonics on the AC side and 100-Hz disturbances in the DC loop. Two methods of mitigating low-frequency resonance were proposed and the effects simulated. Installation of the blocking filter in the neutral bus of the converter station can reduce the amplitude of the resonance overvoltage.

Generalized Input Impedance Modeling of TL-Network-Based HFDPS for Validating Frequency-Dependent Criteria for Power-Signal Integrity

Adjusting the transmission-line (TL) length or using active compensation is pursued in high-frequency-distributed power systems (HFDPSs) as a possible remedy for addressing the TL effects. Although adjusting the TL length is primarily limited to printed-circuit-board (PCB) level implementations, active compensation yields higher expense and complexity. To mitigate TL effects under periodic condition, generalized input impedance modeling of a TL-network-based HFDPS feeding linear load(s) is provided. Using this generalized model, a frequency-dependent criterion for maintaining power-signal integrity is outlined for scenario centric single-/multiple-input single-/multiple-output HFDPS topologies. Selection of such a transmission frequency is important for designing a HFDPS to avoid deterioration of voltage and current, rupturing the TL insulation, and increased losses owing to the TL effect. Validations of the frequency-dependent criteria have been carried out using simulation and experiments in time and frequency domains.

Theory and Experiment of Two-Section Two-Resistor Wilkinson Power Divider With Two Arbitrary Frequency Bands

In this paper, a novel design theory of two-section two-resistor Wilkinson power divider (WPD) is introduced. By selecting two different physical lengths of two-section transmission lines (TLs), two arbitrary frequency band WPD can be achieved. Compared with the former work, the designable frequency ratio range $u$ can be extremely extended from $1 to $1 , general design equations for characteristic impedances, physical lengths, absorption resistors, and frequency ratio ranges are newly derived and proved from even- and odd-mode analysis. Because of no capacitors or inductors, the proposed WPD can be used for high-frequency applications. Spurious band of $S_{21}$ appears between two passbands under the condition of two different physical lengths; therefore, a $\Pi$ -type dual-band transformer is newly introduced to replace single TL for spurious band suppression. We proved that $\Pi$ -type structure could effectively suppress spurious band of $S_{11}$ , maintain two arbitrary frequency passband of $S_{21}$ , and provide an extra isolation band of $S_{32}$ at center frequency. Finally, three proposed WPD examples with $\Pi$ -type structure are selected with different frequency ratios, where frequency ratio $u = 4$ in Example A, $u = 6$ in Example B, and $u = 20$ in Example C are designed and fabricated in the experiment. Measured results show good agreement with the theoretical results.

Research on optimal investment path of transmission corridor under the global energy Internet

Under the background of the global energy Internet, the investment planning of transmission corridor from XinJiang to Germany is studied in this article, which passes through four countries: Kazakhstan, Russia, Belarus and Poland. Taking the specific situation of different countries into account, including the length of transmission line, unit construction cost, completion time, transmission price, state tariff, inflation rate and so on, this paper constructed a power transmission investment model. Finally, the dynamic programming method is used to simulate the example, and the optimal strategies under different objective functions are obtained.

Adaptive Single-Pole Autoreclosing Concept with Advanced DC Fault Current Control for Full-Bridge MMC VSC Systems

This paper presents an adaptive autoreclosing concept for HVDC transmission systems with modular multilevel converters in full-bridge topology for single pole-to-ground faults. Since HVDC transmission will be used in the German energy transmission system to support the heavily loaded ac grid for energy transport over far distances, the interruption time has to be kept as short as possible to preserve system stability. Within the presented autoreclosing concept, the necessary interruption time is determined adaptively. After fault detection, the converter control drives the fault current to zero and injects a low-level ac current. The nonlinear interdependence between the fault arc resistance and the current is used to detect the final arc extinction and to start the voltage recovery, enabling a fast resumption of the power transmission. PSCAD|EMTDC is used to model the electric arc behavior and the dielectric recovery inside an exemplary point-to-point HVDC grid model as an evaluation of the concept. The minimum required ac current is identified related to the used fault detection method. Additionally, the influences of fault position, line length, and fault resistance on fault detection are investigated. The results show that the required interruption time can be determined adaptively for transmission line length up to 400 km.

Designs of Diplexing Power Dividers

A diplexer with different-frequency power dividers cascaded to its output ports can split a signal into different frequency bands for power dividing functions. However, the design of a diplexer usually requires two different frequency filters. This paper presents three new microstrip diplexing power dividers (DPDs) to achieve duplexing power division without requiring additional filters. Moreover, to increase selectivity, each of the proposed DPDs has the flexibility of adding a dual-band filter to its input port. In particular, the proposed DPDs have matching circuits integrated in the dividers, enabling each divider with imaginary input impedance to reach the required open condition; this is achieved by designing a 50- $\Omega $ transmission line of appropriate length or a quarter-wavelength ( $\lambda $ /4) transmission line.

Generalized Dual-Band Unequal Filtering Power Divider With Independently Controllable Bandwidth

In this paper, a novel design method of generalized dual-band unequal filtering power divider (DUFPD) is proposed. Using this method, the power divider (PD) could be designed to realize the dual-band filtering response with arbitrary power division, arbitrary frequency ratio, arbitrary real terminated impedances, independently controllable bandwidth, and excellent isolation. To satisfy these characteristics, a proper dual-band filtering structure is selected to replace the conventional quarter-wave length transmission line in the PD. In addition, a single resistor structure is utilized to obtain effective isolation between the output ports. Furthermore, the complete design procedures and analytical equations of the proposed generalized DUFPD are presented based on the circuit and transmission line theories. To demonstrate the validity of the proposed design method, a DUFPD with different real terminated impedances is designed, fabricated, and measured. We show that there is a good agreement between the simulated and measured results.

Transmission line fault location using traveling wave frequencies and extreme learning machine

In this research, a new approach was proposed for determining the fault location in transmission lines. Traveling wave frequencies and an extreme learning machine (ELM) were used to determine fault location. Transient signals in the time domain were transformed to the frequency domain using the fast Fourier transform (FFT) and the traveling wave frequencies were detected from the transient frequency spectrum. In order to detect the location of fault, traveling wave frequency was used initially to predict the fault location. The prediction of this fault location was tested for many different fault conditions and was found to be adversely affected by only the source inductance value. This is due to the negative effect of source inductance on wave velocity. Regression feature of ELM was used in order to improve the prediction of fault location and to minimize the negative effect of source inductance. For ELM regression training, values of the fault distance estimated from the traveling-wave frequencies and the source inductance values were used as ELM input data, and the actual distance values were used as ELM output data. After ELM regression training, ELM predicted a new fault location using the input data. The Alternative Transients Program (ATP/EMTP) was used to model J. Marti frequency dependent line model, and the MATLAB program was used to perform fault-detection algorithms. Simulation results show that the proposed method is very successful against many variables such as different fault resistances, source inductances, transmission line characteristics, transmission line lengths.

Miniaturised unequal Wilkinson power divider using lumped component elements

A compact two-way unequal Wilkinson power divider with a power division ratio of 2 is proposed. The proposed design can reduce more than 75% of the occupied area, compared with the conventional unequal power divider using composite transmission line. In the proposed design, the total transmission-line length is much less than conventional one. A resistor and a compensative capacitor are used to isolate output ports. The proposed divider is designed, fabricated and tested. The results show that at the designed frequency of 1.5 GHz, the input return loss ( s 11 ) and output return losses ( s 22 , s 33 ) are better than 20 dB and the output ports isolation ( s 23 ) is better than 25 dB.