Coupled Lines Research Articles

Identification of Critical Elements in Interconnected Power Networks

Modern power systems are structurally complex, consisting of elements such as buses, transformers and transmission lines, which are interconnected and liable to failures that could result in total system blackout. Early detection and quick identification of the elements that are critical to the security and reliability of such interconnected power networks is essential for smart grid applications. This paper proposes a Coupling Strength Matrix (CSM) method, which is based on Network Structural Characteristics Theory and the Relative Electrical Distance (RED) between nodes in the network. Two indices, Bus Coupling Strength (BCS) and Line Coupling Strength (LCS), are proposed in identifying the critical transmission lines and weak nodes within a power network. The proposed method is demonstrated on the standard IEEE 30-bus system and 32-bus Nigerian network. The results obtained compare well with that obtained using conventional closeness centrality-based method. This new approach could be useful in quick identification of weak nodes and critical lines that could result in voltage collapse or island formation during critical outages, with less computational burden.

A Feeding Technique for Wideband CP Patch Antenna Based on 90° Phase Difference Between Tapped Line and Parallel Coupled Line

A feeding technique for wideband circularly polarized (CP) patch antenna based on the 90° phase difference between tapped line and parallel coupled line in a feeding network is proposed. The tapped line and parallel coupled line are equivalently regarded as a direct coupling element with 0° phase delay and a J -inverter coupling element with 90° phase delay, respectively. In design, two identical λ /2 resonators are employed to excite two orthogonal modes for wideband equal magnitude. Meanwhile, the feeding lines are tapped and coupled to the two resonators, and tapped line and coupled line can inherently provide 90° phase difference as demanded for CP radiation with no need for an additional delay line or a phase shifter. The whole structure is modeled as an equivalent three-port network, and the theoretical axial ratio (AR) is calculated with the magnitude and phase of the voltage at the radiation conductance. Since two minima in AR response emerge, this proposed patch antenna can achieve a wide AR bandwidth. The theoretical performance is finally verified by a fabricated CP patch antenna prototype with a profile of 0.042 λ 0, and the 3 dB AR fractional bandwidth is 7.07%.

Compact Wideband Differential Bandpass Filter Using Coupled Microstrip Lines and Capacitors

A compact wideband differential bandpass filter (BPF) is achieved by loading two pair of capacitors at different positions of the half-wavelength-coupled microstrip line. The capacitances and loaded positions of capacitors combining with the even–odd-mode impedance of the coupled microstrip line can produce and control the three differential-mode (DM) transmission poles (TPs), four DM transmission zeros (TZs), and three common-mode (CM) TZs. Comparing with the state-of-the-art wideband differential BPFs, the proposed design has the advantages of compact size and low insertion loss. A prototype with the size of 51 mm $\times 4$ mm ( $0.5\,\,\lambda _{ g} \times 0.04\,\,\lambda _{ g} $ , $\lambda _{ g} $ is the microstrip guided wavelength at the center frequency $f_{ 0 }$ ) is designed for demonstration, which exhibits the 3-dB fractional bandwidth of 105% centered at 1.8 GHz and the minimum insertion loss of 0.16 dB.

Study on Reactive Power Imbalance and Its solution of Parallel Coupled Transmission Lines

In view of the imbalance and even the abnormal phenomenon of reactive circulation of parallel high voltage transmission lines with similar measured parameters in actual operation, combined with field investigation and test, theoretical analysis and simulation demonstration, it is clear that this phenomenon is caused by the use of unconventional phase sequence and unreasonable transposition of the two-circuit lines when erecting the same tower. Based on the PSCAD simulation, the corresponding improvement measures are put forward from two aspects of optimizing the arrangement of phases and transposition. The results show that in order to solve the power imbalance problem of parallel coupled transmission lines, it is recommended to optimize the phase sequence of conductors in consideration of economy and operability.

Super rogue waves in coupled electric transmission lines

Coupled electric transmission lines (CETLs), which consist of a great number of identical sections, have been studied theoretically in the present paper. The super rogue wave (SRW) in CETLs is analyzed using the nonlinear Schrodinger equation. The dependence of the characteristics of the SRW parameters on CETLs is displayed in this paper. The results may be useful for exploiting or avoiding SRWs in CETLs.

Wide‐stopband and high selectivity step impedance resonator bandpass filter using T‐network and antiparallel coupled line

A wide-stopband attenuation with high-selectivity step impedance resonator (SIR) bandpass filter (BPF) is presented in this study. The T-network stubs are used to produce transmission zeros (TZs) close to the centre frequency ( f 0 ) with a high-selectivity. Moreover, the antiparallel coupled lines can produce a TZ at spurious frequency of conventional SIR BPF for all step impedance ratio ( K ). For the validation, a half-wavelength ( λ /2) SIR BPF with T-network stubs at the input/output ports was designed at f 0 of 2.6 GHz. From the experiment, the insertion and return losses at f 0 were determined to be 0.91 and 21.25 dB, respectively. The insertion and return losses were better than 1.1 and 16.5 dB, respectively, of the 180 MHz bandwidth. The TZ frequencies ( fZ 1 , fZ 2 , and fZ 3 ) were located at 1.69 GHz (0.63 f 0 ), 2.98 GHz (1.12 f 0 ), and 3.17 GHz (1.19 f 0 ), respectively, with a high selectivity. The stopband attenuation was better than 25 dB from DC to 2.23 GHz and from 2.89 to 9.82 GHz.

High Performance Asymmetric Coupled Line Balun at Sub-THz Frequency

In this paper, we report a high-performance balun with characteristics suitable for future broadband sub-THz differential circuits. The idea of the balun is based on three asymmetric coupled lines, which enhance the odd mode capacitances to equalize the even/odd mode phase velocities. The inner line of the three asymmetric coupled lines is configured to form the open stub ( λ /2), while the outer lines form short stubs ( λ /4). To further reduce the phase imbalance, the short stubs in one of the arms of the balun are connected with vias and a lower metal layer. The balun is developed using the standard 130-nm SiGe BiCMOSback-end process and EM simulated with ADS momentum and Sonnet. The −10-dB reflection coefficient (S 11 ) bandwidth of the balun is 136 GHz (88–224 GHz). It shows insertion loss (including RF pads) <1.5 dB, phase imbalance <7 degrees, and amplitude imbalance <1 dB at 94–177 GHz. Furthermore, a scaled-down version of the balun operates on the WR-6, WR-5, and WR-4 frequency bands without significant degradation in its performance. Such characteristics of the balun make it an ideal candidate for various broadband differential circuits.

Strong spin-orbit coupling and Dirac nodal lines in the three-dimensional electronic structure of metallic rutile IrO2

Using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we have studied the bulk and surface electronic structure of metallic rutile $5d$ transition metal oxide ${\mathrm{IrO}}_{2}$ that harbors both edge and corner sharing Ir-O octahedrons. We observe strong modulation of the band structure by spin-orbit coupling (SOC). The measured band structure is well reproduced by our ab initio calculation without band renormalization, suggesting the absence of the SOC-enhanced correlation effect in ${\mathrm{IrO}}_{2}$. In accordance with the calculation, we visualize two types of Dirac nodal lines (DNLs) protected by mirror symmetry and nonsymmorphic crystal symmetry, respectively. SOC gaps the first type of DNLs, which may contribute largely to the strong spin Hall effect. The second type of DNLs at the edges of Brillouin zone, however, remain intact against SOC. Our results not only provide important insights into the exotic transport properties of ${\mathrm{IrO}}_{2}$, but also shed light on the understanding of the role of SOC in the iridate family.

High‐selectivity bandpass filter using six pairs of quarter‐wavelength coupled lines

A novel high-selectivity bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) using six pairs of quarter-wavelength coupled lines has been presented. By employing two pairs of side-coupled lines and four pairs of open/shorted coupled lines, high roll-off skirt characteristic, and good stopband rejection can be achieved with five TPs and six TZs. Theoretical analysis is explained and simulated results are illustrated for this high-performance filter. Finally, a BPF example with a centre frequency of 1.9 GHz and a 3 dB fractional bandwidth of 9% is designed, fabricated, and measured. It is shown that the measured lower and upper stopband rejections are better than 38 and 16 dB, respectively. Good agreement between the simulations and measurements validates the design method.

Design and Measurement of a 1-bit Reconfigurable Transmitarray With Subwavelength H-Shaped Coupling Slot Elements

A novel 1-bit 256-element reconfigurable transmitarray antenna (RTA) at the Ku-band is presented. The element consists of two orthogonal H-shaped slots as receiving and transmitting structures, and the power transmission is realized by a coupling microstrip line in between. Two p-i-n diodes integrated on the coupling line can be electronically controlled to reverse the excitation directions, thus generating two states with 180° phase difference and low transmission loss. A subwavelength element spacing of $\lambda _{0}$ /3 is utilized to stabilize the element performance under oblique incidence. A transmitarray prototype with $16 \times 16$ elements and aperture size of $5.3\lambda _{0}\times 5.3\lambda _{0}$ at 12.5 GHz is fabricated and measured for the experimental verification. The measured results show that the maximum gain is 17.0 dBi with an aperture efficiency of 14.0%, and 2-D scanning beams within ±50° angular range are obtained. The 3-dB gain bandwidth of the broadside beam is 9.6%.

A G-Band Wideband Bidirectional Transceiver Front-End in 40-nm CMOS

A G-band wideband bidirectional transceiver front-end is proposed. Coupled transmission line (CTL) and the staggered inter-stage wideband matching technique are exploited to extend the bandwidth of low noise amplifier (LNA) and power amplifier (PA). The transmit/receive (T/R) switch is realized as a single-pole-double-throw (SPDT) switch to connect the LNA and PA with good matching performance, low insertion loss, and high isolation simultaneously. The proposed G-band bidirectional transceiver front-end is implemented in 40-nm CMOS and occupies $ {870}\,\, {\mu } \textrm {m} {\times } {910}\,\, {\mu } \text{m}$ die area including the pads. The front-end in the transmitter (TX) mode achieves a measured 3-dB bandwidth of 32.8 GHz with a peak gain of 9.6 dB and a simulated saturated output power of 3.0 dBm, while the receiver (RX) mode features a measured 3-dB bandwidth of 34.8 GHz with a maximum gain of 10.5 dB and a simulated minimum noise figure (NF) of 10.8 dB. The implementation of the bidirectional transceiver front-end demonstrates the feasibility to integrate the TX and RX with a single on-chip antenna in G-band.

Calculation of Distance Protection Settings in Mutually Coupled Transmission Lines: A Comparative Analysis

Protection of mutually coupled transmission lines poses special challenges to protection engineers, since the general principles outlining the expected performance of the protection elements are based on simplified versions of the issues affecting them. Distance protection elements are among the most commonly accepted methods for protecting mutually coupled transmission lines, however, the calculation of settings and the validation of their performance is a complex task, involving lots of simulations and analysis of results to come up with an acceptable solution. Though various methods have been proposed to deal with the problem of calculating the optimal settings of distance protection elements, there is still room for improvement, since these methods have been formulated for the general case considering simple transmission lines. In this paper, a variation of one of these methods is introduced to enhance the computing times and reliability of the solutions for the specific application of quadrilateral distance protection to mutually coupled transmission lines, through the characterization of the expected performance of the operating characteristic, and the formulation of the optimization problem and the solution method. The obtained results show the improvements in computing times and quality of the solution provided by the proposed algorithm.

Parametric studies of ring and parallel coupled line resonators for matched bandstop filter design

Recently, matched bandstop filters had become a substantial part of modern RF and microwave systems. However, in these types of filters, the key problem in the couplings of any microstrip resonators to transmission microstrip line is the variation or tolerance of the coupling gap. It was found that the bandstop response is very sensitive to the gap size of the coupled line. Therefore, this paper presents parametric studies of dual-mode parallel coupled line and ring resonator for matched bandstop filter design. For parallel coupled line resonator, it was found that with careful design and proper circuit parametric study on the coupling spacing, very high notch and matched return loss response were obtained. In contrast, for ring resonator, based on the simulated result, it was found that a very high notch and matched return loss response were obtained with careful design and proper circuit parametric study on the coupling spacing, width at coupling lines, and perturbed stub length.

Equation-Based Solutions to Coupled, Asymmetrical, Lossy, and Nonuniform Microstrip Lines for Tab-Routing Applications

In this paper, analytical equation-based solutions are derived to allow quick and accurate calculations directly from the physical parameters of coupled, asymmetrical, lossy, and nonuniform microstrip lines with interdigital trapezoidal tabs incorporated, resulting in their corresponding scattering parameters. Capacitance and inductance matrices under a quasi-static condition are derived from the cross-sectional dimensions of asymmetrical coupled microstrip lines with unequal widths. They are converted into a frequency-dependent resistance–inductance–conductance–capacitance model, allowing complete equation-based solutions to their four-port Z-matrix, S-matrix, and ABCD-matrix. As an application example of tackling the complexity of transmission lines, the derived analytical method is applied to a transitional structure with linearly varying trace width in tabbed microstrip lines by the method of segmentation. In addition, a new concept of tab-coupling fringing capacitance is specifically introduced to compensate for underestimated mutual capacitance at tab positions, which will improve the accuracy of the proposed approach. Numerical modeling results from commercial simulation tools are compared for validation purposes. As a conclusion, the proposed method and its versatility are demonstrated with applications to practical high-speed and high-density printed circuit board designs, which renders itself effective and efficient in an optimization process.

Design of wideband four‐way filtering power divider based on SIW loaded square patch resonator

A new design of wideband four-way filtering power divider (FPD) based on substrate-integrated waveguide (SIW) loaded square patch resonator is presented. The wideband operation is realised by utilising the TM 20 mode of the patch and the TE 110 mode of the SIW cavity resonator. Afterwards, the selectivity is obtained by adding four open-ended coupling lines to each side of the square patch. Besides, an extra isolation network is introduced between each output port. To verify the design concept, a prototype of the proposed FPD operating at 3.55 GHz with a fractional bandwidth of 21.3% is fabricated and measured. Results indicate that the input return loss is >10 dB and the insertion loss is 0.3 dB and 3°, respectively. Both simulated and measured results are in good agreement.

Wideband filtering power divider with wide rejection bandwidth and isolation

A wideband filtering power divider (FPD) with wide rejection bandwidth and good isolation is presented, based on conventional Wilkinson structure. Parallel coupled lines and two pairs of open-circuit stubs are used for achieving bandpass filtering response and enhancing the performance of the rejection bandwidth. Furthermore, by properly choosing two resistors between two pairs of open-circuit stubs allows good isolation performance. Measured results indicate that the FPD operates at 2.35 GHz ( f 0 ) with a − 20 dB bandwidth of 55.3%. In the upper stopband range from 3.7 to 8.8 GHz (3.74 f 0 ), the minimum rejection is 20 dB. Within working band, the isolation between the output ports is higher than 24 dB. In addition, ultra-wide isolation better than 20 dB from DC to 10 GHz is obtained.

CMOS Millimeter-Wave Ultra-Wideband Bandpass Filter With Three Reflection-Zeros Using Compact Single TFMS Coupled-Line Hairpin Unit

In this brief, a modified coupled-line (CL) hairpin unit topology with short-circuited ends is proposed to design a compact millimeter-wave ultra-wideband (UWB) bandpass filter (BPF). Thin film microstrip configuration is used for the implementation of CL hairpin unit. The passband return loss bandwidth is enhanced by three attenuation poles achieved by appropriately selecting a single set of CL impedances. Explicit design equations along with graphs are provided by using even-and-odd mode analysis. A prototype filter is fabricated using 0.35- ${\mu }\text{m}$ BiCMOS technology. The fabricated UWB BPF achieves an extended passband from 25 GHz to 95 GHz around 60 GHz with more than 115% fractional bandwidth along with a wide return loss bandwidth. The filter size is very small with the overall width comparable to the width of a 50 ${\Omega }$ line. The measured results are in good agreement with those of predicted ones up to 110 GHz.

Modeling a Planar Coupled Microstrip Lines using various Wavelets and Method of Moments

In this paper, we apply a several wavelets basis functions to the method of moments to modeling the parallel-coupled microstrip lines. The first set of equations is for the shielded microstrip line solved with moment’s method and wavelets. The Green’s function is obtained from the theory of images. The second set are for the parallel-coupled microstrip lines operating in the TEM mode or when the analysis can be based on quasi-static approximation, the properties of coupled lines can be determined from the self- and mutual inductances and capacitances for the lines. To demonstrate the effectiveness and accuracy of the proposed technique, numerical results of even- and odd-mode characteristic impedances, coupling coefficient, percentage sparsity achieved in the impedance matrix, the CPU Time to reverse impedance matrix, and error relative for Daubechies, Coiflets, Biorthogonal and Symlets wavelets are presented. Numerical results are in good agreement with those in previous publications.

Compact tunable dual/Tri‐band bandpass filters with multiple zeros

Here, compact dual/tri-band bandpass filters (BPFs) with tunable passbands are proposed. The multiband BPFs are designed by combining a BPF with tunable passband and a BPF with fixed passband using a common external coupling line. The former consists of a dual-mode resonator loaded with varactors (DMVLR) and the latter is composed of a quad-mode resonator (QMR). The classical analysis method of odd/even mode is employed to analyse the characteristics of the resonators. The centre frequency (CF) of the tunable passband can be easily tuned by varying the voltage imposed on the varactors. A constant absolute bandwidth (CABW) is obtained over the whole tuning range of frequency by properly adjusting loading positions of the varactors. The single and dual-passband BPFs with fixed passband are obtained by designing the parameters of QMR appropriately. Simulation and measurement results show that the proposed BPFs are of high selectivity, and the resultant filters are of compact size. In addition, the proposed multiband BPFs have four transmission zeroes (TZs). There are two self-adaptive TZs on both sides of the tunable passbands, which are generated by the multipath coupling structure.

Microstrip quad‐channel diplexer using quad‐mode square ring resonators

AbstractA new compact microstrip quad‐channel diplexer using quad‐mode square ring resonators (QMSRRs) is proposed. The quad‐channel diplexer is composed of two QMSRRs. A structure consists of two QMSRRs together with one common input and two output coupling lines is proposed, which can remove the matching network and therefore reduce the absolute size of the diplexer. The proposed QMSRR has two transmission zeros at the frequencies between the four resonant frequencies, which can be controlled by changing the length and impedance ratio of the QMSRR. Simulation and measurement results show that the resultant diplexer is of a small circuit size and a high isolation.