Uniform Line Research Articles

Propagation Constant Measurement of Microwave Networks With Symmetric/Asymmetric Reflections

We proposed a Line-Line (LL) method for complex propagation constant $\gamma $ determination of uniform transmission lines or uniform lines loaded by samples having symmetric or asymmetric reflections using calibration-free scattering (S-) parameter measurements. To achieve our goal, we first derived pseudo wave-cascading-matrix (WCM) presentation of a network modeling a uniform line with asymmetric reflections ( $S_{11} \ne S_{22}$ ). Then, we proved that such a network can be represented by the product of three matrices: two matrices for impedance transitions and one matrix for phase and amplitude changes. While the first impedance transition matrix is a $2\times 2$ square matrix with unity values at diagonal entries and two different reflection coefficient values at off-diagonal entries, the second one is the inverse of the first one. Besides, the phase-amplitude change matrix is a diagonal matrix with diagonal entries corresponding to phase and amplitude changes. Next, using such representation of the pseudo WCM, we implemented the LL method to determine $\gamma $ of a network with asymmetric (or symmetric) reflections by a simple trace operation (summation of the diagonal terms in a square matrix) without resorting to ascertaining the reflection coefficient corresponding to an impedance transition. The method was validated by $\gamma $ measurements of an empty waveguide section with length 7.70 mm, the same section loaded by a polyethylene sample, and another waveguide section with length 10.16 mm loaded by bianisotropic metamaterial slabs in C-shape form.

Study of a miniaturized dual-beam TWT with planar dielectric-rods-support uniform metallic meander line

A dual-beam planar dielectric-rod-support uniform metallic meander line slow-wave structure (SWS) for high-efficiency Ka-band traveling wave tube (TWT) is proposed in this paper. Two dielectric rods are placed on both sides of metallic meander line to support it, instead of the dielectric substrate in the conventional microstrip meander line. Furthermore, it can not only solve the problem of the electron charge accumulation on microstrip but also leads to a bigger interaction impedance. According to particle-in-cell simulation results, a dual-sheet-beam planar dielectric-rod-support uniform metallic meander line TWT can get an output power of 330.2 W at 38 GHz under the case of 10.6 kV beam voltage and 0.2 A beam current. The corresponding maximum gain and electron efficiency are 23.4 dB and 15.5%, respectively, where the length of whole SWS is only 20 mm.

Helping Students Learn About Electromagnetics [Book/Software Reviews

The reviewer of the book Conceptual Electromagnetics notes that the book describes the fundamental subject of electromagnetics, or field and wave theory, for an undergraduate college class using very advanced teaching and learning methods. It provides abundant opportunities for instructors to introduce innovative lectures, in-class and homework assignments, and tests (including those for online distance education and for students pursuing independent learning). An active teaching and learning methodology is built into this text by means of interactive in-class questions, explorations, and discussions. The book also includes peer instruction, allowing students to tutor one another. The learner-centered pedagogies and practices - and active teaching and learning, in particular - are very effective, motivational, and positively evaluated by students. There are many conceptual questions as well as multiple-choice ones that focus on core concepts of the material, requiring conceptual reasoning and understanding. This book is organized into 12 chapters on electrostatics fields, steady electric currents, magnetostatic fields, time-varying electromagnetic fields, uniform plan electromagnetic waves, transmission lines, waveguides and cavity resonators, and antennas and wireless communication systems. For many engineering students, the fields and waves, or electromagnetics, course is particularly challenging. But, with the author' advanced teaching and learning approach, this course can be pleasant and fun. His teaching technique should become the standard for all science and engineering courses.

Processor dependent bias of spatial spectral estimates from coprime sensor arrays.

Coprime sensor arrays (CSAs) can estimate the directions of arrival of O(MN) narrowband plane wave sources using only O(M+N) sensors with the CSA product processor. Processing data from a finite aperture array effectively smears the true spatial power spectral density (PSD) with a kernel function determined by both the array geometry and the processing of the signals observed by the array. This paper examines the asymptotic behaviors of the kernel functions resulting from two different processors applied to a CSA sampling geometry in the limit of large aperture. The kernel functions of the product processed CSA and conventionally beamformed coprime sensor arrays (CBF CSA) are compared to the baseline of the kernel of a densely populated uniform line array (ULA) of similar aperture. At the limit of large aperture, the product processed CSA estimate is asymptotically unbiased like the ULA, while the CBF CSA estimate is not. The PSD estimates computed from the CSA processors are compared when spatially correlated Gaussian noise is an input to the array to highlight the bias issues.

Wave dynamics on networks: Method and application to the sine-Gordon equation

We consider a scalar Hamiltonian nonlinear wave equation formulated on networks; this is a non standard problem because these domains are not locally homeomorphic to any subset of the Euclidean space. More precisely, we assume each edge to be a 1D uniform line with end points identified with graph vertices. The interface conditions at these vertices are introduced and justified using conservation laws and an homothetic argument. We present a detailed methodology based on a symplectic finite difference scheme together with a special treatment at the junctions to solve the problem and apply it to the sine-Gordon equation. Numerical results on a simple graph containing four loops show the performance of the scheme for kinks and breathers initial conditions.

An experimental study of pneumatic extruding direct writing deposition-based additive manufacturing

A pneumatic extruding direct writing deposition process is proposed in this paper. Compressed high-purity nitrogen was selected as a driving force to squeeze a liquid metal out of a nozzle. Combining this step with movement of the underlying substrate enabled the formation of metal patterns. Four nozzles with different structures were employed in this research, and the effect of the structural design of the nozzle on the flow of the liquid metal was analyzed both theoretically and experimentally. The influence of the distance between the nozzle and the substrate on the deposited metal lines was also investigated. To demonstrate a practical application, several metal patterns were successfully fabricated, each with a uniform and continuous metal line. Furthermore, three-dimensional objects were also fabricated. The results of a morphological analysis of the deposited metal lines show that the throttle channels added to the nozzle significantly decrease the flow of the metal fluid; as a result, nozzles with throttle channels produce thinner metal lines. The distance between the nozzle and the substrate influences the outline of the cross section of the deposited metal lines without significantly decreasing the outflow of the liquid metal.

Numerical analysis of deposition frequency for successive droplets coalescence dynamics

A pseudopotential based multi-relaxation-time lattice Boltzmann model is employed to investigate the dynamic behaviors of successive droplets’ impact and coalescence on a solid surface. The effects of deposition frequency on the morphology of the formed line are investigated with a zero receding contact angle by analyzing the droplet-to-droplet coalescence dynamics. Two collision modes (in-phase mode and out-of-phase mode) between the pre-deposited bead and the subsequent droplet are identified depending on the deposition frequency. A uniform line can be obtained at the optimal droplet spacing in the in-phase mode (Δt* < 1.875). However, a scalloped line pattern is formed in the out-of-phase mode (Δt* > 1.875). It is found that decreasing the droplet spacing or advancing contact angle can improve the smoothness of line in the out-of-phase mode. Furthermore, the effects of deposition frequency on the morphology of the formed lines are validated to be applicable to cases with a finite receding contact angle.

Miniaturization of Broadband Wilkinson Power Dividers

This paper proposed three modified Wilkinson power dividers in order to achieve a size reduction and a wide bandwidth. The first structure presented the power divider using compact folded step impedance transmission lines rather than the uniform microstrip line design for operating center frequency of 3 GHz. The second structure showed the power divider with delta-stub for 2.4 GHz. Finally, the third modified structure introduced the two-section Wilkinson power divider using series-delta stub for center frequency of 2.4 GHz as well. The study managed to get an overall dimension of 15 mm × 9.5 mm for the first proposed design achieving a reduction of 75.6 % and fractional bandwidth of 133 %. For the second proposed structure, the size was 15 mm × 15 mm with a reduction of 56 % and fractional bandwidth of 56 %. While the third design size was 17 mm × 15 mm with a reduction of 63.6 % and the structure achieved a broadband bandwidth with fractional bandwidth of 220 %. The proposed power dividers used RT/duroid 5880 substrate with a thickness of 0.38 mm. Simulation and measurement results indicated that the modified power dividers showed equal power division, good phase balance, high isolation between output ports, and good return loss better than -12 dB covering the operating frequency range<strong>.</strong>

Genetic resource management for enhancing saffron productivity in Jammu and Kashmir

Lack of high yielding cultivars due to triploid nature of saffron is a major concern of low productivity. To explore and utilize available genetic variability in natural populations of Jammu and Kashmir, about 2500 saffron accessions collected from saffron growing areas of Jammu and Kashmir during 2002-2006 were subjected to variability and divergence studies at genetic and molecular level. Selected lines from natural population exhibited a wide range of variability for economic, morphological and corm attributing traits indicating considerable scope for saffron improvement through clonal selection. Selection scheme for more yield gains have been designed. Stability analysis of 10 elite divergent lines confirmed that behavior of tested lines was predictable over environments for floral and yield attributing characters. Considering the desired population mean coupled with non-significant bi (equal to unity) and deviation from regression (S2di) equal to zero, two lines viz; SMD-45 and SD-3 were observed to be well adapted to all the environments. The results revealed average stability of all lines for these traits except for number of radical leaves and corm yield plot-1 (SD-3). Comparison of different stability models in terms of their relative performance for different traits under study produced uniform information and ranked lines without any major disagreement. Line SMD-45 was observed to be the most stable having high saffron yield.

Optimization Algorithm for DOA Estimation of a Shallow Sea Target Based on Active Time Reversal

Time reversal technique is applied to the DOA estimation of a shallow sea target, and a method based on active time reversal (ATR) is proposed to achieve correct estimation under multipath and low signal-to-noise (SNR) conditions. Combining the classical ray theory with array signal processing theory, the conventional multipath DOA estimation model based on uniform line array and the ATR-based DOA estimation model are set up respectively. The Capon algorithm is employed to simulate the models and compare it with conventional one. The simulation results show that the ATR-based estimation model can better estimate the azimuth angle of the target than the conventional counterpart, provide higher resolution and better suppress side lobes with the same signal-to-noise ratio (SNR), especially the low SNR.

New investigations on the method of characteristics for the evaluation of line transients

The method of characteristics (MoC) transforms line equations into ordinary differential equations, and the numerical transient solution is typically performed through discretization in time and space. There exits also a version of MoC proposed in the literature, in which the discretization in space is eliminated for uniform lines. This has the potential to render the MoC faster than the traveling wave-based models. This paper examines in detail the possibility of removing spatial discretization and extends the application for the evaluation of transients on cables in addition to transients on lines. It has been demonstrated that, although removing spatial discretization is possible by introducing certain change of variables and approximations, the resulting model has limited numerical precision and may show numerically unstable behavior. This is principally due to the approximation error introduced by the linearization of differential equations, necessary to obtain a relationship between line ends. The paper discusses other sources of numerical errors and shows that the line needs to be subdivided to improve precision.

Sound-structure interaction analysis of an infinite-long cylindrical shell submerged in a quarter water domain and subject to a line-distributed harmonic excitation

The sound-structure coupling problem of a cylindrical shell submerged in a quarter water domain is studied. A semi-analytical method based on the double wave reflection method and the Graf's addition theorem is proposed to solve the vibration and acoustic radiation of an infinite cylindrical shell excited by an axially uniform harmonic line force, in which the acoustic boundary conditions consist of a free surface and a vertical rigid surface. The influences of the complex acoustic boundary conditions on the vibration and acoustic radiation of the cylindrical shell are discussed. It is found that the complex acoustic boundary has crucial influence on the vibration of the cylindrical shell when the cylindrical shell approaches the boundary, and the influence tends to vanish when the distances between the cylindrical shell and the boundaries exceed certain values. However, the influence of the complex acoustic boundary on the far-field sound pressure of the cylindrical shell cannot be ignored. The far-field acoustic directivity of the cylindrical shell varies with the distances between the cylindrical shell and the boundaries, besides the driving frequency. The work provides more understanding on the vibration and acoustic radiation behaviors of cylindrical shells with complex acoustic boundary conditions.

Rapid surrogate-assisted design optimization of minimum-size broadband branch-line couplers with variable topology

This work discusses simulation-driven design of miniaturized wideband branch-line couplers with a variable topology. Size reduction is enabled here by replacing uniform transmission lines of the original coupler with slow-wave structures in the form of cascaded compact cells and meander lines. The primary goal is to determine a number of cells in the cascade and particular cell dimensions for which the minimum size of the coupler as well as its required operating conditions are ensured. To this end, we employ a surrogate-assisted technique involving a trust-region gradient search framework. Computational efficiency of the design process stems from estimating the Jacobian of circuit responses at the level of a low-fidelity model of the cascade. The latter is composed in a circuit simulator from duplicated EM-evaluated data blocks of a single cell and is well correlated with the corresponding high-fidelity model. The key advantage of this work is the utilization of a reconfigurable, cheap, and well-aligned low-fidelity model. The proposed approach is demonstrated through design of a minimum-size two-section branch-line coupler with quasi-periodic dumbbell-shaped cells and meander lines. Excellent circuit performance as well as its small size showcase the reliability and usefulness of the presented method. Experimental verification is also provided.

Perturbative Analysis of Differential-to-Common Mode Conversion in Asymmetric Nonuniform Interconnects

In this paper, a perturbative technique and the related computational algorithms are presented for the prediction of differential mode (DM) to common mode (CM) conversion arising from asymmetry and nonuniformity in differential interconnects. It is shown that discontinuities evolving from nonuniformities and geometrical imbalance along the (usually desired uniform) lines give rise to equivalent distributed sources that couple the (ideally decoupled) DM and CM circuits. The prediction of modal quantities is then achieved numerically, as an iterative perturbative refinement of the frequency response of an ideal differential line. Different levels of approximation are introduced and discussed. Specifically, the assumption of weak imbalance allows analyzing the propagation of the two modes separately. Moreover, the assumption of weak nonuniformity allows avoiding CM refinements. The proposed technique applies to both ideally uniform and inherently nonuniform interconnects, and leads to a significant simulation speed-up compared to traditional approaches that analyze nonuniform lines by their subdivision into uniform sections. The methodology is illustrated based on two differential microstrip lines, one tapered and one with sinusoidally varying trace edges. Validation against full-wave simulations and measurements is provided.

Passive Intermodulation Due to Conductor Surface Roughness

The physical mechanism of the experimentally observed dependence of passive intermodulation (PIM) in printed circuits on conductor surface roughness is studied. It is shown that electrothermal (ET) nonlinearity, arising due to heating of imperfect conductors by high-power carriers in a multicarrier system, is correlated with conductor surface roughness and has a unique signature. Carriers modulate the conductor resistivity, skin depth, and surface impedance which generate PIM products. The detailed analysis demonstrates that ET-PIM depends on the conductor resistivity, shape, and roughness profile and also on the electric and thermal properties of the substrate. Their effects on PIM are illustrated by examples of uniform microstrip lines with different conductor and substrate materials, and periodically perturbed and meandered microstrip lines.

Fabrication of fine metal patterns using an additive material extrusion process with a molten metal

The objective of this work is to establish a volumetric metal 3-dimensional (3D) printing system based on material extrusion method and to fabricate metal patterns by investigating various process variables. Numerical heat transfer simulation was conducted to design the nozzle system with a minimized heat loss at the nozzle tip. Based on the simulation results, a metal 3D printing system with X, Y, and Z stages was constructed. The effects of lead content in molten metals and printing conditions such as stage speed and flow rate were investigated. The line formation like bulged, uniform, and dashed lines was evaluated using an optical microscope, and the variation in line widths of uniform lines was investigated with the process variables. Various types of 2-dimensional (2D) patterns were fabricated with an optimized process variable. A simple 3D structure was obtained to demonstrate the feasibility of the proposed system and procedure.

Longitudinally Uniform Transmission Lines With Frequency-Enabled Mode Conversion

A class of longitudinally uniform transmission lines with low loss, low dispersion, and high-field confinement, called mode-selective transmission lines (MSTLs), has been proposed for ultra-broadband and ultra-fast electromagnetic signal guidance and processing. Their operation is mainly based on the concept of frequency-enabled mode selectivity. This paper presents our latest research results on this emerging MSTL, including its operating mechanism, propagation characteristics, higher-order modes, and transition design. Throughout the detailed discussion, two MSTL structures operating in distinct frequency ranges (DC to 60 GHz and DC to 500 GHz as showcased here) are considered. First of all, a comparative study among MSTLs and several conventional transmission lines is made, illustrating significant differences in structural features, wave guidance, field distributions, and frequency characteristics. Second, the phenomenon of mode selectivity occurred in MSTLs is examined by means of identified physical evidence (i.e., field distributions in connection with modal behavior) and theoretical foundation. It is verified that, with increasing frequency, the dominant modes of MSTLs are converted from a quasi-TEM microstrip mode to a quasi-TE10 waveguide mode over a certain frequency range. Following this thread, a more rigorous analysis is carried out by defining and formulating three characteristic frequencies based on the observed inherent physical dispersions, and the operating frequency ranges of MSTLs are thus divided into several distinct frequency regions associated with the frequency-related variable dominant mode. In addition, a general analysis of the attenuation characteristics of MSTLs and higher order modes in MSTLs is conducted. To facilitate practical measurements and to expedite the integrated applications of MSTLs, we propose a low-loss and ultra-broadband transition between MSTL and microstrip line, through which undesired higher order modes are effectively suppressed. The numerical and theoretical analyses of MSTLs are carried out with experimental verifications. At the end of this paper, different fabrication and measurement techniques for the two MSTLs of interest are briefly described.

Deconvolved Conventional Beamforming for a Horizontal Line Array

Horizontal line arrays are often used in underwater environments to detect/separate a weak signal and estimate its direction of arrival from many loud interfering sources and ambient noise. Conventional beamforming is robust but suffers from fat beams and high-level sidelobes. High-resolution beamforming, based on the inverse of the signal covariance matrix, such as minimum-variance distortionless response (MVDR), yields narrow beamwidths and low sidelobe levels but is sensitive to signal mismatch and requires many snapshots of data. This paper applies a deconvolution algorithm used in image deblurring to the conventional beam power of a uniform line array (spaced at half-wavelength) to avoid the instability problems of common deconvolution methods. The deconvolved beam power yields narrow beams, and low sidelobe levels similar to or better than high-resolution beamforming and at the same time retains the robustness of conventional beamforming. It yields a higher output signal-to-noise ratio than conventional (and MVDR) beamforming for isotropic noise. Performance is evaluated with simulated and real data.

Performance Analysis for Focused Beamformers in Passive Underwater Acoustic Localization

Focused beamformers are widely used in passive underwater acoustic localization. Many pseudo-peaks (spurious peaks not corresponding to a real source) are produced by focused beamformers, impacting the performance and reliability of related algorithms. After describing both the received signal model of near-field sources with a uniform line array, and the basic principle of passive localization based on focused beamformers, we define pseudo-peaks in the focused beamformer’s spectra and give the procedure to quantify these pseudo-peaks. The performance of conventional focused beamformers (C-FBs) and minimum variance distortionless response focused beamformers (MVDR-FBs) are studied, focusing on the number of pseudo-peaks in passive underwater acoustic localization. After establishing a simulation model based on an underwater acoustic environment, the algorithms are compared in terms of signal-to-noise ratio, frequency, distance of the source signal, and detection threshold. In all cases, the MVDR-FB method shows superior performance to the C-FB method in minimizing the number of pseudo-peaks. Finally, a method of selecting the detection threshold based on the convergence of pseudo-peak number is proposed.

Comments on “Microstrip T-Junction Power Divider With Exponentially Tapered Transmission Lines”

In the above paper, Smith and Sigmarsson [1] proposed a T-junction unequal power divider using exponentially tapered transmission line (ENTL) and uniform transmission line (UTL). However, the cutoff wavelength $\lambda _{c}$ defined in [1] and also in [2] , from which the definition of $\lambda _{c}$ has been adopted, are incorrect. So the entire analysis and design equations of [1] are questionable. Also, the authors have not shown the amplitude and phase imbalance variation over the frequency.