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Purpose: Experimental results and numerical simulations are presented, concerning effects of microwave generation in coaxial transmission lines which are fed with unipolar, high voltage electric pulses. The work is aimed at clarifying the relative importance of several mechanisms that could be responsible for the appearance of microwave-frequency oscillations in the course of pulse propagation through the guiding structure. Design/methodology/approach: Dispersive and filtering properties of coaxial waveguides that involve three structural sections are discussed. These latter follow one another along the axis of symmetry. Two identical sections at the input and output are filled with an isotropic liquid dielectric, while the middle part may, in addition, be either partially or fully filled with a non-conductive gyrotropic material. The inserted core represents a set of ferrite rings showing a nonlinear response to the initial high voltage, pulsed excitation. Throughout the series of measurements, the diameters of the inner conductor and of the ferrite core were kept constant. The outer conductor’s diameter was varied to permit analysis of the effect of that size proper and of the degree to which the cross-section is fi lled with ferrite. The gyrotropic properties of the ferrimagnetic material were realized through application of a magnetic bias field from an external coil. The measurements were made for a variety of pulsed voltage magnitudes from the range of hundreds of kilovolts, and magnetic bias fields of tens kiloamperes per meter. Findings: As observed in our experiments, as well as in papers by other writers, a unipolar pulse coming from the radially uniform front-end section, further on gives rise to quasi-monochromatic voltage oscillations. These appear as soon as the pulse has advanced a sufficient distance into the radially nonuniform portion of the guide. The oscillations may consist of a small number of quasi-periods, which suggests a large spectral line width. However, by properly selecting geometric parameters of the wave guiding line and the characteristics of the initial pulsed waveform it proves possible to obtain output frequencies of about units of gigahertz and pulse powers at subgigawatt levels. Conclusions: The frequencies and amplitudes of the appearing oscillations, as well as their spectral widths, are governed by the complex of dispersive and non-linear properties of the guiding structure. The diameters of the inner and outer coaxial conductors in the line, diameter of the ferrimagnetic insert and its intrinsic linear dispersion determine the set of waveguide modes capable of propagating through the line. An oscillating part of the waveform may appear and get separated from the main body of the pulse if it has originated at a higher frequency than the cut-off value for a different mode than the initial TEM. Key words: unipolar pulse, coaxial transmission line, microwave frequency oscillations, dispersion laws, waveguide modes

The following study investigates the use of a coaxial transmission line for determining the properties of powdery dielectric materials (1-10GHz). Four powdery materials with dielectric constants ranging from 3.5 to 70 (SiO$_2$, Al$_2$O$_3$, CeO$_2$, and TiO$_2$) were experimentally investigated at varying volume loading fractions. Powder particles were mixed with a paraffin matrix and properties of the powder were analyzed using ten mixing equations to verify their accuracy. These powder-paraffin composites were also modeled at varying volume loadings for comparison with experimental data to gain a better understanding of the interactions between the different phases. The optimal volume loading fraction was determined to be 10% for all powders tested. A metric for selecting the most well-suited mixing equation was proposed that involved taking the ratio of the particle dielectric to that of the matrix. This study ultimately provides guidance for experimentally measuring the dielectric properties of unknown powdery materials that have application for new devices that utilized powder-based dielectric materials.

Compact re-entrant cavities, widely used as microwave resonators, can be employed as high-performance sensors. A new approach is proposed here to calculate the resonance frequency, its sensitivity, and quality factor ( $Q$ -factor) of these cavities, having diverse taper shapes of the re-entrant post. The proposed closed-form expressions are based on the chain matrix approach for tapered coaxial transmission lines, and the calculated results for the resonance frequency and quality factor have been verified with full-wave electromagnetic simulations and experiments. The formulation is mathematically simple and accurate (< 4%). Since a cavity with taper toward the gap-end is found to be more sensitive to gap variations, a robust, tunable re-entrant cavity resonator with a tapered post and an adjustable gap was fabricated. The performance of this cavity as a displacement sensor was evaluated by numerically calculating the deflection of a thin diaphragm from measured resonance frequencies using the expressions derived here. This design of the sensor is found to be immune to manufacturing tolerance in the re-entrant gap.

We previously reported on the complex permittivity and dc conductivity of waste-activated sludge. The measurements, spanning a frequency range of 3 MHz to 40 GHz, were made using an open-ended coaxial transmission line. Although this technique is well established in the literature, we found that it was necessary to combine methods from several papers to use the open-ended coaxial probe to reliably characterize biological samples having a high dc conductivity. Here, we provide a set of detailed and practical guidelines that can be used to determine the permittivity and conductivity of biological samples over a broad frequency range. Due to the electrode polarization effect, low frequency measurements of conducting samples require corrections to extract the intrinsic electrical properties. We describe one practical correction scheme and verify its reliability using a control sample., 28 pages, 10 figures

The design of a resonant slot array antenna in a single layer ridge gap waveguide is presented. Linear and planar array configurations are developed. The linear array includes eight series slots in the ridge gap waveguide that is powered by a coaxial transmission line. The planar antenna array is developed by incorporating a power divider of four branches in the ridge gap waveguide layer. Each branch of the power divider feeds the linear array. The planar antenna detail design for Ku-band is provided, and the manufactured antenna is measured. The antenna impedance bandwidth of 7% at 13.5 GHz centre frequency, the gain of 20.5 dBi and the side lobe level of

A pulse-charged coaxial transmission line test stand was developed to evaluate the loss and saturation characteristics of the magnetic core material Vitroperm 500Z under square-pulse excitation (SPE) conditions. The test stand was developed to generate a 100 kV square pulse that was discharged into the primary winding of a Vitroperm magnetic core load. The magnetization rates achieved ranged from 5 to $50~T/\mu s$ , and saturation times ranged from 40 to 100 ns. The design of the SPE test stand is discussed, and experimental results for the Vitroperm core material are presented.

The electromagnetic shielding behavior of fabrics woven with carbon/stainless steel/polypropylene (C/SS/PP) hybrid yarns were investigated in the frequency range of 300 kHz to 1.5 GHz. This study mainly emphasizes the electromagnetic shielding behavior of C/SS/PP hybrid yarn fabric and the effect of different fabric parameters such as pick density, fabric architecture and number of fabric layers on shielding effectiveness (SE) of fabrics with C/SS/PP hybrid yarns. The SE of fabric samples were tested by a vector network analyzer using a coaxial transmission line tester. In addition, surface images of different fabric structures were examined to appreciate the effect of yarn floats on the shielding behavior of fabrics. From the SE test, it was observed that an increase in pick density increases the SE of C/SS/PP hybrid yarn fabric due to addition of carbon and SS content in the fabric. Besides, the fabric cover and pore area distribution are also changed for varying pick densities. Essentially, a fabric’s architecture plays an important role in the fabric cover and pore area distribution. The one-end float (1/1 plain) fabric of 6.3 ppcm provides higher shielding of 88.44 dB than a 4-end (4/1 twill) or 7-end float (8-end satin) fabrics of 6.3 ppcm. Moreover, an increase in the number of fabric layers also improves the SE of fabrics. The developed C/SS/PP hybrid yarn fabric can be used for shielding wireless transmissions, radar transmissions and for shielding panels.

In this paper the modeling and the design of a microwave sensor is proposed for real-time fuel quality monitoring, with particular regard to water-in-fuel measurement. A mechanical and fluid-dynamic design has been performed, evaluating the stiffness, the robustness of the sensor structure and the pressure field acting on it. Furthermore, an electromagnetic study has been carried out to verify the validity of the physical measurement principle. The adopted procedure involves the modeling of the sensor in CAD and the simulation of its behavior. The sensor, based on microwave transmittance, is attractive because of its simplicity and foreseeable low cost.

The paper presents methodologies and results concerning one- and two-dimensional numerical modeling of radio frequency oscillations in a coaxial transmission line fed with a short pulse of electric current. The line is partially filled with a ferrite material, magnetized longitudinally close to saturation. The 2D model has permitted analyzing, for the first time in the art, the spatial structure and dynamics of the wave field within the radially non-uniform cross-section planes of the non-linear and dispersive guiding structure. This opens ways for optimizing size parameters of the line and the extent to which it is filled with the ferromagnetic material, thus increasing the line’s electric strength and intensity of the r.f. oscillations.

A novel method for complex permittivity and permeability measurements of dielectrics has been shown. The method is based on a previously developed transmission-line technique, however, has been modified to allow for dielectric properties estimation with measurements of reflections only. The analysis of measurement errors, resulting from: sample length uncertainty, vector network analyzer uncertainty, and open-end inaccuracy, has been shown in the article. The calibration method using open/short/offset-short standards has been described. The method has been experimentally tested by measurements of three different reference liquid samples. A good agreement between measured values and previously published ones has been obtained. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:727–732, 2014

Infinite 2D periodic EBG structures from coaxial metal cylinders placed in a planar waveguide are investigated. Short-circuited and open-circuited metal cylinders forming, respectively, short-circuited and open-circuited sections of coaxial transmission lines are considered. It is shown that, by varying the lengths of these coaxial lines, it is possible to create defects in EBG structures that form regular waveguides. The eigenmodes of such waveguides are studied. It is shown that the EBG structures formed from coaxial metal cylinders can be used as the base for the development of multifunction microwave devices.

Time domain reflectometry (TDR) is commonly used for several monitoring applications, particularly in hydrology and soil science for soil water content evaluation. Furthermore, significant advantages of TDR methodology, such as its relevant performance characteristics in terms of high flexibility and high sensitivity, as well as a non-destructive detection approach, render this technique an appealing candidate for a variety of environmental and industrial applications. In a previous paper [A. Cataldo, L. Tarricone, F. Attivissimo, A. Trotta, Simultaneous measurement of dielectric properties and levels of liquids using a TDR method, Measurement, doi:10.1016/j.measurement.2006.11.006 ] the authors demonstrated that TDR can be successfully used for a simultaneous real-time qualitative and quantitative monitoring of liquids. In this paper, a rigorous metrological characterization of the proposed method is formulated, and the uncertainty contributions are identified. The obtained results, confirm that the system is definitely adequate for simultaneously measuring dielectric constants and levels of liquids, with the associated relative uncertainties of 2% and 3%, respectively, for all the considered liquid samples. This way, challenging perspectives for several monitoring applications are open, especially in the processing of industrial liquids.

In the coaxial transmission line method, a factor that greatly influences the accuracy of the results is the air gaps between the material under test and the coaxial transmission line test fixture. In this paper, we discuss the influence of the air gaps and the measures that can be taken to minimize that influence when Mn-Zn ferrites are measured. We propose an improved simulation model of the coaxial transmission line test fixture holding the material under test in which the air gaps are filled with conductive materials. By combining the improved simulation model, the mode-matching method, and the Newton-Raphson method, the Mn-Zn ferrites' intrinsic complex permeability and permittivity can be determined accurately, even if the conductor-filled gaps are quite wide. We also examine the influence of the finite conductivity of the coaxial transmission line test fixture. We manufactured a coaxial transmission line test fixture to measure the intrinsic complex permeability and permittivity of Mn-Zn ferrites in the frequency range from 10 to 200 MHz. The intrinsic values thus determined have been experimentally verified. We describe the structure of the test fixture, its calibration issues, and the experimental results.

In this article, mixtures of water and ethylene glycol, in which the concentrations of ethylene glycol are about 37%, 50%, 60%, and 70%, were used as the dielectric of coaxial transmission lines. The pulse breakdown strength, effective time to breakdown, relative permittivity, resistivity and freezing temperature of the mixture have been studied experimentally.

Time-domain-reflectometry (TDR) measurements, which were originally used to locate and diagnose faults in transmission lines, have been widely applied in geology and soil science for accurate and flexible measurements of soil moisture and water content. Furthermore, the most attractive advantages of TDR rely on the possible determination of the spatial location and nature of various objects, both in real time and with a nondestructive approach. This makes the TDR technique an appealing candidate for a variety of environmental and industrial applications. Although the TDR instruments are commonly used to date, particularly for the aforementioned purposes, the state of the art is rather lacking in liquid-monitoring applications. This paper describes how the suitable combination of TDR detecting functionalities can lead to a simultaneous monitoring of quantitative and qualitative properties of liquid samples. In fact, the proposed TDR method allows, in one shot, the measurement of liquid levels, the determination of multiple interfaces in layered media, and the evaluation of dielectric properties such as dielectric permittivity or electrical conductivity. Some applications to real cases are proposed, which are referred to petrol–chemical mixtures or water-based liquids, thus validating the approach on a wide range of materials.

In this paper, we compare analytical and optimizing reconstruction methods for the electrical permittivity of materials. The reconstruction is done from the measured S-parameters of a coaxial transmission line. We compare the different reconstructions on materials of known electromagnetic properties, air, and ethanol. We conclude that two methods, one analytical (propagation matrices) and an optimization (L/sub 1/ norm), are the most appropriate for the reconstruction of permittivities, whether these are low-loss and constant over the frequency range or highly lossy and frequency dependent.

Miniature rectangular coaxial transmission line (with a 300 × 300 μm outer conductor) is simulated, fabricated, and tested up to the Ka band. It is made by the electrochemical fabrication (EFAB™) of nickel such that the center conductor is supported primarily by ≈λ/4 stubs that also establish a resonant passband. The minimum insertion loss of a 1.67-cm-long test structure is found to be 1.74 dB at the passband center of 29 GHz. This is within 0.57 dB of the lowest insertion loss predicted by full-wave numerical simulations, indicative of the high precision and smooth surface morphology of the EFAB process. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 365–368, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11383

The main goal of this letter is the analysis of the multipactor effect within a coaxial waveguide structure when an external axial dc magnetic field is applied. We have designed and manufactured a coaxial waveguide sample that has been immersed within a long solenoid. Numerical and experimental results confirm a significant change in the RF breakdown behavior with regard to the case without the axial dc magnetic field, as well as the existence of single- and double-surface multipactor regimes. Good agreement between theory and experimental data has been found., Manuscript received January 23, 2012; accepted January 31, 2012. Date of publication March 16, 2012; date of current version April 20, 2012. This work was supported in part by the Spanish Government through R&D project TEC2010-21520-C04-01. The review of this letter was arranged by Editor E. A. Gutierrez-D.

This article introduces a 20-μm tall, 75-μm wide rectangular polyimide core micro coaxial transmission line that can be realized using a simplified fabrication procedure. Measurements of a 4-bend, meandered micro coaxial line demonstrate an 8% increase in the insertion loss and a 2% variation in the phase compared with a straight line of equivalent length. Cross-coupling below 30 dB up to 65 GHz has been measured between two micro coaxial lines separated by 175 μm. These properties make the structures as useful building blocks for highly miniaturized and integrated microwave circuitry. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1291–1293, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25212

In this article, we propose a new method to measure the complex relative permittivity (er = e − je) and permeability (μr = μ − jμ) of liquid- or powder-type materials using a two-port probe which is constructed from coaxial transmission lines. The two-port probe is a simple structure that can be easily fabricated with low cost in comparison with conventional probes which are the type of the cavity and waveguide. And we have adopted the Cole–Cole equation and air-filled coaxial cable for calibrating the proposed probe. To verify the performance of the proposed probe, we measured the properties of materials in the form of liquids and powders and compared the results with those measured by the air-filled coaxial cable, which shows good agreement. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2977–2979, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24793

Broadband permittivity measurements made by eleven organizations using the transmission/reflection (T/R) method are compared to high-accuracy cavity resonator results. T/R accuracy is less than 10% for /spl epsiv//sub r//sup '/ >

In this article, we present a very simple toolkit for permittivity and permeability measurement in the microwave region in real time. This kit contains a coaxial cell and a dedicated software compatible with any Vector Network Analyzer (VNA) for the reconstruction of permittivity and permeability data. The customizing design of the coaxial cell depends on the applications and material forms. The dedicated software for overall cells reconstructs directly in real time the permittivity and the permeability from the S-parameters measured. The Nicolson & Ross-Weir algorithm is using after a de-embedding process done by modeling our cell with an identity card (IC). The novelty of our method is that, after calibration process of the VNA to remove the cable effect, the measurement of the permittivity and permeability were done directly after only one measurement in real time. To validate the accuracy of this new measurement process for new applications, we reconstruct the permittivity of two material forms (dielectric or/and magnetic solids, semisolid). This new toolkit is called EpsiMu (www.epsimu.fr). © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2643–2648, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25570

This paper introduces a newly constructed type-N coaxial microcalorimeter that will serve as a primary power standard in Korea Research Institute of Standards and Science. The detailed design scheme of the microcalorimeter is presented, and its characteristics are evaluated. The performance of an adiabatic line was simulated with a finite-element-method-based tool and predicted. The measured insertion loss of the assembled adiabatic line was less than 0.15 dB. Frequency and power sweep measurements were performed on a reference standard to find a substituted power level that minimized the dual-element error. We also propose evaluation standards that can be used for the measurement of radio frequency loss. The correction factor for the effective efficiency of the reference standard was experimentally evaluated. We also present an uncertainty evaluation process and the corrected effective efficiency of a type-N coaxial reference standard.

A new quasianalytical method, the multipole theory (MT) method, is described for the computation of cutoff wavenumbers of TE and TM modes in a rectangular coaxial transmission-line family. An extensive comparison with the exact data of the literature and various configurations of a rectangular transmission-line family shows the accuracy and flexibility of the quasianalytical MT method. It has been shown that the MT method is an effective approach for the analysis of TE and TM modes in a rectangular transmission-line family. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 405–407, 2000.

The complex permittivity of water is measured at 2.45 GHz and 10 GHz over the temperature range 10°C to 80°C using short circuited coaxial transmission line method. Water has high dielectric consta...

The Physikalisch-Technische Bundesanstalt and the National Institute of Standards and Technology have compared microwave noise power in coaxial transmission lines. Each laboratory measured two solid-state noise sources at 2.0 GHz, 4.0 GHz, and 8.0 GHz relative to their primary thermal noise standards. The agreement between laboratories is better than 0.07 dB, which is within the stated uncertainties of the two services, namely +or-0.06 dB for NIST, and +or-0.04 dB for PTB (confidence level: 0.95). >

Dielectric properties of grapes at 2.45 GHz were measured at moisture contents varying from 80 to 15% (wet basis) at temperatures ranging from 25-80 degrees C using the Open Ended Coaxial Transmission Line Technique. Both dielectric constant and loss factor decreased with decreasing moisture content. In low moisture samples these properties were found to be considerably influenced by higher temperatures. Dielectric properties of sugar solutions of varying concentrations (20-250% by weight in water) were also determined at different temperatures, and these values were compared to those of grapes of corresponding moisture concentration. Predictive models of the dieletric properties as functions of moisture content and temperature were generated using response surface methodology. The results are useful in estimating the volumetric heating of grapes by microwave energy, and these methods can be extended to sugar-based foods in general.

The theory and design of dielectric beads in a coaxial transmission line are discussed. At first the theory of many dielectric beads in a transmission line are discussed briefly. It is shown that by proper choice of the spacing between the adjacent beads the overall reflection produced by all the beads can be minimized. The case of an optimum bead producing minimum reflection is discussed in detail. Broadband characteristics of such a bead is also studied. Finally, the actual design of a bead is carried out.

The paper concerns the results of design and performance of a low power coaxially interdigital magnetron with external coupled cavity. Special attention is given to the problem of wide-range tunability, in the microwave frequency spectrum, using either mechanical or voltage-tuning methods. The basic structure of the magnetron consists of a short, hermetically-sealed section of coaxial transmission line which contains six equally spaced radial vanes extending from the inner wall of the outer coaxial cylinder into six longitudinal slots in the inner coaxial cylinder. The cathode is symmetrically located within the inner coaxial cylinder at the position of the multianode structure. This sealed off multi-anode system is used to excite a TEM mode in an external coaxial circuit. Experimental results on electronically and mechanically tunable operation are reported, with particular emphasis on voltage tuning.

The complete radiation field of a tubular monopole of arbitrary length and radius, which is base driven by a low-impedance coaxial transmission line, is derived. The integral equation for the current distribution, which includes a term for the feed-point correction is solved by the inversion of a matrix under the assumption that the current is a continuous, piecewise linear function. The far-zone electromagnetic field established by this current is expressed in closed form. It is found that the effect of thickness is to round off the nulls predicted by previous theory for vanishingly small radius and to enhance the high-angle radiation.

Numerical "shooting" methods are employed in obtaining the dispersion curves of a coaxial waveguide loaded with a radially inhomogeneous dielectric. The utility of this technique is tested by comparing results with known analytical solutions. The method is also used to find the dispersion curves of a coaxial waveguide loaded with a radially Gaussian-distributed plasma.

The shielding effectiveness of a 'pigtail' connection between a coaxial transmission line and a ground plane is treated rigorously by the method of moments, as a function of the type and number of pigtails and frequency. Numerical results show that the type of pigtail connection is crucial with regard to radiation and shielding effectiveness, even though the pigtail itself does not radiate significantly. All pigtails are not equal, even though they can be short electrically. A short pigtail is significantly better than a longer one. A long pigtail connection can actually enhance radiation. Finally, multiple pigtails yield significant improvement over the single pigtail only for short pigtails. Numerical and experimental results are compared and found to be in good agreement. >

The effective position of the open circuit in precision 7-mm 50-Ω coaxial transmission line is found experimentally to be located beyond the physical end of the center conductor by a distance 1.198+2.69×10-10f2 millimeters at f megahertz (

The letter gives the simple analytical closed-form expressions for odd-and even-mode impedances for coupled rods in closed rectangular coaxial line by taking into account the sidewall effect on coupled slab lines.

The results of an International Intercomparison of RF voltage at 1 GHz is described. Differences between values reported by the five participating laboratories fell within the total uncertainties given by these laboratories. The estimated limits of uncertainty given by the laboratories varied from a few tenths to several percent.

This Special Issue of the Transactions on Microwave Theory and Techniques in observance of the first 100 years of the IEEE has an especially interesting parallel for the history of guided electromagnetic (EM) waves. It was in this decade 100 years ago that Heinrich Hertz, a German professor of physics, carried out his original experiments which demonstrated the reality of the Faraday-Maxwell theory of the wave nature of light and electricity and the central thesis that they are essentially the same. According to Hertz, the result of the experiments is to confirm the fundamental hypotheses of the theory. He acknowledged the problems of following Maxwell's difficult style, with its "unwonted mathematical difficulties," and of not always being quite certain of having grasped the physical significance of Maxwell's statements.

This work describes a regression method for determining, to a good approximation, the parameters of an adapter from banana plugs to a coaxial connector from a measurement of the input admittance of one of two identical adapters separated by a set of Lecher lines of different lengths. The method has been experimentally proved.