Method to Avoid Star Point Data Reflections

In this study, a low-pass filter with coaxial transmission lines is designed and produced. The objective for designing a coaxial low-pass filter was to utilize both low loss transmission and high breakdown voltage capability for high power microwave applications to enable the suppression of the second harmonic of the 4.4-6 GHz C-Band ( C-Band was selected as a proof of concept ) signals with minimal insertion loss. Microwave and 3D electromagnetic simulators were used in the filter design. The design was started by establishing an 11 th order Chebyshev low-pass filter prototype giving 0.05 dB ripple. Based on this prototype, a filter circuit consisting of capacitors and inductors as lumped elements was designed. The low and high impedances to be selected for the stepped impedance method, which is the basis of the transition to coaxial transmission lines, were decided and the most suitable impedances for manufacturing was determined. The filter using these impedances and designed with stepped impedance lines was transformed into the filter in which coaxial transmission lines are used. Coaxial transmission lines in the low-pass filter circuit consist of conductors with an insulating material in between. While the insulating material is selected as air in the high impedance sections of the transmission lines, it is PTFE (Polytetrafluoroethylene) with an insulating constant of 2.1 in the low impedance sections. The designed filter was manufactured. The basic properties of the manufactured filter were characterized by using RF measuring devices and compared with the designed filter. The measurements results prove that the frequency responses of the designed filter and the produced filter are very close to each other. Namely, a low-pass filter with a cutoff frequency of 6 GHz, a sharp suppression of about 45 dB at the stopband of 9 GHz and a return loss of 20 dB was designed and produced by using coaxial transmission lines. The novelty in our work can be stated that the power handling capability is increased by two techniques. The first one is that the highest transmission line radius preventing the higher order mode excitations is used to decrease the conductor loss. Teflon is covered around the low impedance lines to enhance the dielectric breakdown capability. Teflon inclusion is also used to decrease the practical low impedance level that improves the filter characteristics.

In an electrically large square coaxial transmission line, we demonstrated preservation of a narrow impulse during propagation through a relatively tight 90° bend compensated by a layered approximation of a CID lens. By use of a non-linear global optimization algorithm, we established that the layered dielectric design was essentially optimal. In terms of the observed, raw impulse response, the compensated bend increased the pulse width by only 15 ps, to 70 ps, from the 55 ps observed for an equivalent length of straight transmission line. In contrast, without compensation, the transmission line bend distorted the impulse into a bipolar signal spread over a 500 ps time interval.

Impedance matching with an adjustable segmented transmission line

The novel Surface-Volume-Surface Electric Field Integral Equation (SVS-EFIE) has been recently proposed for accurate extraction of per-unit-length (p.u.1.) inductance and resistance (RL) matrices in multi-conductor transmission lines (MTL). The SVS-EFIE yields the same accuracy of RL extraction as the traditional volumetric EFIE (V-EFIE) solution while introducing the unknown currents on the conductor surface instead of its volume. This work presents detailed discussion of Method of Moments (MoM) discretization of the SVS-EFIE and resultant matrices. The example of a coaxial transmission line is utilized in derivations to demonstrate method's applicability to MTL's with multi-connected cross-sections.

The design method of TEM transition from circular section to rectangle section is presented. To achieve good transition two design principles are constructed. Firstly, the section shape between circle and rectangle section should change slowly. Secondly, impedance of transmission line with arbitrary section between circle and rectangle coaxial transmission line should be kept exactly same impedance. The VSWR computing result validate the method of TEM transition from circular section to rectangle section.

A TEM cell is a rectangular or square coaxial transmission line tapered at each end to form a closed cell. The one end of the cell can be fed with a signal generator and the other end can be terminated by a resistor load equal to the characteristic impedance of the line (Crawford, IEEE Trans Electromagn Compat 16(4):189–195, 1974) [1]. Between the inner conductor (the septum) and the top and bottom plates, a field propagates from the source to the termination as a planar field in free space. Transverse electromagnetic (TEM) cells are used to generate uniform EM waves in a shielded space. The cell has a tapering section at each end, so that the rectangular coaxial transmission line is able to adapt to standard coaxial connectors (Tippet and Chang, Radiation characteristics of dipole sources located inside a rectangular, coaxial transmission line, 1976) [2]. TEM cells are used for Radiated emission and Radiated immunity testing of small products, for biomedical experiments, and for calibration of RF probes/sensors. The wave propagation inside the cell is similar to far-field plane propagation in free space and the wave has an impedance of free space, i.e., 377 Ω [1]. The cutoff frequency of the cell depends upon its dimensions. This is the limitation of the cell because this constrains the size of a product and we can test within the cell. The TEM cell designed is considered to be of an open type.

In coaxial transmission lines, the inner conductor is commonly supported by dielectric beads spaced at intervals along identical sections of line. At microwave frequencies, where the bead spacing is large compared with the wavelength, there result sharp peaks of reflection corresponding to reinforcement of the reflections of individual beads. Assuming that the reflections of the beads themselves have been reduced to a uniform minimum by careful design and production control, it is advantageous to disperse the beads in each section so as to reduce the cumulative reflection peaks. A dispersal has been found which is believed to yield the minimum value of peak reflection.

The work is devoted to a numerical study of runaway electron kinetics in atmospheric pressure nitrogen at the initial stage of radial breakdown in a coaxial transmission line with a wave impedance of 45 Ohm. The study was performed within the framework of the axisymmetric 2D-3V (two coordinates and three velocity components) Monte Carlo model. The problem statement considered the presence of a 0.3‑mm‑thickness disk-shaped electric field enhancer located at the inner conductor of the coaxial line. The enhancer protruded above the inner conductor of the line by 2.5 mm. The space area near the enhancer was considered to be a source of runaway electrons. In addition, the presence of a strong axial homogeneous magnetic field near the amplifier was taken into account. The magnetic field induction varied from 0.15 T to 2 T. The voltage between the line conductors was set in the range of 100-150 kV. Within the simulation, the motion of fast electrons in the coaxial gap was considered, taking into account their scattering on gas molecules and interaction with homogeneous magnetic and inhomogeneous electric fields. It was shown that, within the system under consideration, runaway electrons never reached the anode, i.e. the outer conductor of the coaxial line, if the magnetic field induction was greater than ~0.25 T. In turn, if the magnetic field induction was >0.5 T, the runaway electron radial drift was suppressed at all; however, there was an axial drift with a velocity of ~8 mm per 100 ps. Based on the simulation results, a qualitative description of three scenarios of the dielectric strength violation in magnetically insulated air-filled coaxial lines was proposed. The obtained results explain the results of recent experiments on the study of the coaxial air-filled duct breakdown.

A method for subnanosecond pulse measurements of I-V characteristics is described. The sample is mounted at the end of a transmission line and the incident and reflected pulse is observed. In this way the sample resistance is compared with the known impedance of the coaxial transmission line and no current measuring series resistance is needed. Short pulse risetimes (170 psec) are obtained and difficulties which arise from the current measuring resistor, like temperature dependence and nonlinearity at high currents, do not obscure the measurements.

The characteristic impedance of rectangular coaxial transmission lines can be readily and accurately computed by a simple equation when the capacitance per unit length is known. While the capacitance per unit length of the parallel sides is easily calculated, the calculation of the corner capacitance is a more difficult problem. This problem has been solved by Skiles and Higgins, using orthonormal block analysis. By using their formulas, the corner capacitances for a wide range of all variables were evaluated by means of a digital computer. The results are cataloged in graphical form.

While revising and editing the above paper, Fig. 5 was inadvertently duplicated. The result of this oversight can be seen on p. 980, where the illustrations for Figs. 4 and 5 are the same. The intended Fig. 4, with its caption, is shown below.

Summary form only given. A laser fired through the atmosphere can generate a plasma by freeing charge carriers from the air molecules in the path of the beam. The characteristics of this plasma, especially the delay time between the propagation of the laser and initiation of the arc, were investigated. These plasmas were generated by focusing the output of a KrF excimer laser (248 nm wavelength, 20 nsec (FWHM) pulsewidth) operating between 200 and 525 mJ per pulse with a cylindrical lens generating a line focus across an air gap at the end of a ten foot section of four inch co-axial transmission line. The gaps tested were 4 mm, 8 mm or 11 mm in length, with the center conductor of the line connected to a variable high voltage DC power supply. The arc was detected by measuring current with a B-dot probe mounted near the gap inside the transmission line. To obtain accurate timing results with respect to the laser pulse a UV photodetector was utilized to trigger the oscilloscope. This probe measured delays that ranged between 72 and 412 ns. The delay time increased with increasing gap length and decreased with increasing laser pulse energy and applied voltage.

An examination of the properties of longitudinally-magnetized ferrite in coaxial transmission lines reveals regions of low and high attenuation which could be used for the ON and OFF conditions, respectively, of a switch. A strip line switch designed for fast switching and L band is described. Its performance includes approximately 0.l-db insertion loss and 45-db isolation over a 13 per cent band.

A portable high-voltage (HV) pulsed generator has been designed for rock fragmentation experiments. The generator can be used also for other technological applications. The installation consists of low voltage block, HV block, coaxial transmission line, fragmentation chamber, and control system block. Low voltage block of the generator, consisting of a primary capacitor bank (300 μF) and a thyristor switch, stores pulse energy and transfers it to the HV block. The primary capacitor bank stores energy of 600 J at the maximum charging voltage of 2 kV. HV block includes HV pulsed step up transformer, HV capacitive storage, and two electrode gas switch. The following technical parameters of the generator were achieved: output voltage up to 300 kV, voltage rise time of ∼50 ns, current amplitude of ∼6 kA with the 40 Ω active load, and ∼20 kA in a rock fragmentation regime (with discharge in a rock-water mixture). Typical operation regime is a burst of 1000 pulses with a frequency of 10 Hz. The operation process can be controlled within a wide range of parameters. The entire installation (generator, transmission line, treatment chamber, and measuring probes) is designed like a continuous Faraday's cage (complete shielding) to exclude external electromagnetic perturbations.

This paper presents a uniform model for the LEMP breakdown current normalized waveform reconstruction based on the lightning TEM multi-fractal model. Firstly, the length of the lightning discharging channel is estimated by the lightning engineering model and the coaxial transmission line (TL) model. Secondly, the lightning length model and the TEM multi-fractal model are applied to the lightning electromagnetic pulse (LEMP) breakdown current waveform reconstruction with the first and subsequent return strokes. Finally, it is found that the LEMP breakdown current waveform can be taken as an envelope of a sum of a series of superposed leaders or strokes sub-discharging breakdown currents with the overlapped life time.