Outer Conductor Research Articles

Dual-Polarized Bandpass Frequency-Selective Surface With Quasi-Elliptic Response Based on Square Coaxial Waveguide

A new dual-polarized 3-D frequency-selective surface (FSS) with quasi-elliptic bandpass response is proposed by virtue of the square coaxial waveguide (SCW). By utilizing the SCW as one propagation path in the unit cell, two resonators can be generated intrinsically without introducing any extra structures. In addition, the parallel-plate waveguide constructed by sandwiching the ABS frame between outer conductors of adjacent SCWs will provide a second propagation path and create another resonator. With the help of these resonators, a passband with two transmission poles can be obtained. Furthermore, there are two finite transmission zeros locating at both sides of the passband due to the fact that the signals passing through these two propagation paths are combined out of phase, leading to both-sided sharp roll-off skirt. The E-field analysis and equivalent circuit model presented offer a physical insight into the operating principle of the proposed 3-D FSS. For the purpose of validation, the FSS is fabricated through the 3-D printing technique. The measured results exhibit high frequency selectivity, dual polarizations, and stable bandpass response under a variation of the incidence angle.

A novel sensor using VHF zigzag‐slotted leaky coaxial cable for intruder localization

AbstractThe sensors used in the field of traditional security warfare are often constrained by environmental factors such as weather, light and terrain. In order to solve this problem, a new perimeter intrusion detection system sensor is urgently needed. Based on the theory of the array antenna, leaky coaxial cable (LCX) with periodic zigzag‐slotted outer conductor is designed, its coupling loss is simulated by the software Ansoft HFSS. For evaluating the coupling loss of the LCX comprehensively, the LCX is simulated and measured in four directions, the measured results of coupling loss are 64.1 dB, 62.6 dB, 64.3 dB, 57.2 dB in rotary, horizontal, vertical, and radial direction, respectively. With the research on LCX wireless sensing techniques, a novel LCX sensor is designed and a new approach of localization is put forward. When the intruder enters into the surveillance, the proposed LCX sensor can achieve to detect and locate the intruder by emitting the LFM pulse signal whose working frequency is in VHF, pulse compression is used to improve the detection performance of the intrusion detection system (IDS). The positioning accuracy of the IDS is within 0.8 m, and the range distance is 6.64 m.

Modeling and Dispersion Analysis of Coaxial Lines With Higher Symmetries

In this paper, 1-D periodic structures possessing higher symmetries are proposed and investigated in terms of their dispersion properties. The proposed structures are coaxial lines with coaxial rings periodically loaded on their inner or outer conductors. The higher symmetries, namely, glide and twist symmetries, are obtained by performing an additional geometrical operation within the unit cell of the periodic structure. We demonstrate that the propagating modes exhibit a lower frequency dispersion in higher symmetric coaxial lines. Moreover, the conventional stopbands of periodic structures at their Brillouin zone boundaries can be controlled by breaking the higher symmetry or changing the order of the twist symmetry. A circuit-based analytical method is proposed to calculate the dispersion diagram of the glide-symmetric coaxial lines. The results are validated with a full-wave simulation. Moreover, several prototypes of the twist-symmetric coaxial lines are manufactured and measured. A remarkable agreement is achieved between the measurements and simulations, validating the theoretical results. The proposed structures find potential applications in leaky-wave antennas and fully metallic reconfigurable filters and phase shifters.

A Minimally Invasive Coax-Fed Microwave Ablation Antenna With a Tapered Balun

We present a minimally invasive coax-fed dipole antenna with a tapered slot balun for microwave ablation (MWA) applications. The balun is created by gradually tapering the outer conductor of the coaxial feed line into two parallel strips, leaving two tapered slots on the outer conductor. Implementing the balun within the outer conductor of the coax itself helps reduce the overall diameter of the antenna compared to interstitial antennas that use conventional coaxial baluns. The tapered-slot balun connects the dipole antenna comprised of three active segments to the coaxial feed line. One active segment is defined by an extension of the inner conductor of the coaxial cable, acting as one arm of the dipole. The other two active segments are located in the two slots created by tapering the outer conductor and connected to its distal end to constitute the second arm of the dipole. We designed the antenna to operate at 6 GHz in ex vivo bovine liver and fabricated a prototype to conduct ablation experiments. Simulation and experiment results show that the tapered balun provides good impedance matching between the coaxial feed line and the dipole and helps the antenna achieve localized ablation zones. The proposed antenna offers a promising solution for reducing the overall diameter, and the invasiveness, of coax-fed interstitial antennas used for MWA.

Coaxially Fed Monopole Antenna With Choke Structure Using Left-Handed Transmission Line

A composite right/left-handed (CRLH) transmission line (TL) is proposed for a choke structure. The dispersion relation of the CRLH TL is designed with the left-handed (LH) branch at around 700 MHz. The proposed CRLH TL is applied to the choke structure. The radiation patterns and current distributions on the outer conductor of the coaxial cable are calculated to verify the operation of the choke structure. The characteristics of a conventional sleeve antenna are calculated and compared with those of the proposed antenna. To verify the simulation results, the proposed antenna is fabricated. The $|S_{11}|$ characteristics, the radiation patterns, and the total antenna efficiency are measured. At 585 MHz, the length of the monopole and the choke structure using LH TL are 0.12 and 0.05 wavelength, respectively.

Properties of the RF transmission line of a C-shaped waveguide

A new type of waveguide, named the C-shaped waveguide (CSWG), has a structure similar to that of a coaxial line but with a plate connecting the inner conductor to the outer conductor. The CSWG has unique characteristics, such as a cutoff frequency and easy cooling of the inner conductor, that are absent in the coaxial line. The results of calculations using 3-dimensional simulation software and measurement with the CSWG model are in good agreement with the analytical solution. The CSWG can be applied to a pickup port with a high-pass filter that can attenuate the higher-order modes over the cutoff frequency without attenuating the accelerating mode.

A numerical study of the efficiency of a cylindrical electromagnetic shield

Electromagnetic shields are widely used for protecting electrical equipment and cable lines from the influence of natural and artificial electric and magnetic fields. A 3D mathematical model of a solid cylindrical shield for protection from the effect of an alternating electromagnetic field produced inside a cable has been proposed. The model has been constructed using the finite-element method in the ANSYS HFSS software. Two electromagnetic-field sources have been considered: noise in the inner conductor (cable core) and a coaxial circuit, in which the shield is an outer working conductor. The electromagnetic-field distribution over the cable is described by the Maxwell equations, which are transformed into the Helmholtz vector equation with respect to the electric-field component so that the finite-element method may be used. The electromagnetic parameters of the considered media are constant and isotropic. The shielding properties have been studied for a copper cylindrical shield in the frequency range of 1–100 MHz. As a result of the mathematical solution, the distributions of electromagnetic-field intensities in the model have been obtained. To determine the shielding properties of a cable, the transfer impedance and shielding attenuation have been used. The adequacy of the model and technique for determining the efficiency of the screening has been verified by means of comparison between the obtained data and results of the analytical model.

МОДЕЛИРОВАНИЕ ПРОЦЕССА ИЗМЕРЕНИЯ ПОЛОЖЕНИЯ ГРАНИЦЫ РАЗДЕЛА ДВУХ СРЕД В ЕМКОСТИ С ПРИМЕНЕНИЕМ РАДИОЧАСТОТНОГО МЕТОДА

The article describes modeling of the process for measurement of interface position between two media, in particular two immiscible liquids with different density, one over the other, contained in a tank using radiofrequency method. In this case it is provided invariance of measurement results to electrical parameters of both media. Independent sections of transmission lines with end horizontal sections are used as sensors. To provide invariance to electrical parameters of the lower medium there are used natural resonance frequencies of the two sections of a transmission line or phase shifts of electromagnetic waves with fixed frequency excited and received at the section inputs and reflected from section ends. Functional conversion of informative parameters helps to determine interface position between two media in the tank. In the modeled measurement process in order to provide invariance to electrical parameters of two liquids there are placed vertically three sections of a coaxial or two-wire transmission line. Due to the availability of horizontal end sections at all three transmission line sections, there is no uncertainty of measurement results when measuring the interface position at its zero-, or close to zero, readings in the course of functional processing of resonance frequencies of the three transmission line sections. These sections may be done identical with equal end horizontal parts of a fixed length but with different reactive loads at the ends of horizontal parts. Between parallel outer conductors of coaxial line sections up to the ends of their horizontal parts, electromagnetic oscillations are excited as in a two-conductor line section having end reactive load that is different from the end reactive loads of coaxial line sections. This provides the difference of three dependencies of corresponding resonance frequencies on coordinate of interface position between two media. Determination of interface position in the modeled measurement process on the base of this method is characterized by higher measurement accuracy, easy realization of radiofrequency devices and is free from shortcomings of other radiofrequency methods.

A 57GHz overmoded coaxial relativistic backward wave oscillator with high conversion efficiency and pure TM01 mode output

A 57GHz overmoded relativistic backward wave oscillator (RBWO) operating on the quasi-TEM mode with pure TM01 mode output is presented in this paper, by using outer trapezoidal slow wave structure (SWS) with large distance between inner and outer conductors. The large overmoded ratio can be obtained in coaxial devices to improve power handling capacity, while the large distance between inner and outer conductors can guarantee the electron beam transmit effectively. The 8π/9 mode of quasi-TEM synchronously interacts with the electron beam, while the TM01 mode diffracted by the quasi-TEM mode outputs. The existence of TM01 6π/9 mode in SWS can extract energy from the quasi-TEM mode (which has a high value of Qe) thus increasing the power handling capacity. Particle-in-cell simulation shows that generation with high power 560 MW and efficiency 43.5% is obtained under the diode voltage 520 kV and current 2.47 kA. And the microwave has the pure frequency spectrum of 56.8 GHz radiates in the pure TM01 mode (about 98%).

A novel L-band coaxial transit-time oscillator with tunable frequency

A novel L-band coaxial Transit-time Oscillator (TTO) with mechanical frequency tunability is put forward and analyzed. A smooth inner conductor is adopted, and its radius is tenth of the one of the outer conductor. Compared with the traditional coaxial TTO with gaps in the inner conductor, the vertical distance between the outer and inner conductor is longer, as a result, higher power capacity is achieved. With the diode voltage and current as 600kV and 13kA, respectively, an L-band output microwave with frequency of 1.48 GHz and power of 3.2 GW is achieved. The efficiency can be 41%. Furthermore, by modulating the radius of the outer conductor, the working frequency ranges from 1.38 GHz to 1.52 GHz while the output power is higher than 1.0 GW. The frequency tuning range of the coaxial TTO is 9.5% of the central frequency. Besides, the electric field distribution is analyzed and shows that the longitudinal and transverse working modes are TM01 and π mode, respectively.

Flexible tension sensor based on poly(l-lactic acid) film with coaxial structure

We have developed a tension sensor with a coaxial structure using a narrow slit ribbon made of a uniaxially stretched poly(l-lactic acid) (PLLA) film for application to a wearable device. The tension sensor is produced as follows. We used tinsel wire as the center conductor of the sensor. The tinsel wire consists of a yarn of synthetic fibers arranged at the center, with a spirally wound rolled copper foil ribbon on the side surface. Next, slit ribbons obtained from a uniaxially oriented film of PLLA are wound helically on the side surface of the center conductor in the direction of a left-handed screw, at an angle of 45° to the central axis. The rolled copper foil is used as an outer conductor and covers the yarn without a gap. The prototype of the fabricated tension sensor has good flexibility, since the sensor is in the form of a filament and consists of a highly flexible material. For the 1 mm tension sensor, it was found that for a tension of 1 N, a charge of 14 pC was output. It was also found that the sensor maintained its room-temperature sensitivity up to 60 °C. Compared with an existing coaxial line sensor using poly(vinylidene fluoride) (PVDF), the sensor using PLLA does not exhibit pyroelectricity, meaning that no undesirable voltage is generated when in contact with body heat, which is a significant advantage as wearable sensors. The result has demonstrated the potential application of the PLLA film to wearable devices for detecting heartbeat and respiration.

A Hybrid Slot/Monopole Antenna With Directional Heating Patterns for Microwave Ablation

We present a new coax-fed interstitial antenna for generating directional heating patterns during microwave ablation. The antenna comprises a base-fed monopole wherein, a portion of the outer conductor is extended to create a reflector that directs the fields toward the opposing direction. To further direct the fields away from the reflector, we etched a semicylindrical slot in the outer conductor. The electric field produced by the slot constructively interferes with the field generated by the monopole in the desired radiation direction, while destructively interfering with the monopole’s field behind the reflector. This creates directional specific absorption rate and heating patterns. In addition, the reflector and slot suppress the unwanted currents along the antennas feeding cable. This eliminates the need for a balun and reduces the overall antenna diameter. The antenna is impedance matched using an internal $\pi $ - matching network. A prototype of this antenna, designed to operate at 7 GHz in egg white, was fabricated and used to perform ablation experiments at a power level of 20 W for 5 min. Experimental results agree well with simulations and confirm the capability of the antenna for generating directional heating patterns.

A Wideband Millimeter-Wave Substrate Integrated Coaxial Line Array for High-Speed Data Transmission

Substrate integrated coaxial line (SICL) is a kind of planar transmission line, which can guarantee the propagation of transverse electromagnetic mode wave within a wide band. In this paper, a multichannel SICL array with coaxial lines placed in both vertical and horizontal directions is proposed for high-speed parallel data transmission. The adjacent channels of the SICL array share outer conductors for high-density integration. Moreover, the outer conductor is enhanced by metal fence to suppress the crosstalk between adjacent channels of the SICL array. In addition, a quasi-coaxial transition is designed for the proposed SICL array. A systematical design procedure is given to determine the physical dimensions of SICL array with transitions. The SICL array has flat group delay so that data can be transmitted without significant phase distortion. It is suitable for high-density integration and high-speed data transmission due to the low crosstalk and high bandwidth. To verify the advantage of the proposed SICL array, a $15 \times 3$ channel prototype is designed and fabricated in low temperature co-fired ceramic. The measured S-parameters agree well with the simulated results. The maximum bandwidth of a single channel of the SICL array is up to 56 GHz and the coupling of adjacent channels in the SICL array is less than −30 dB. Data rate of 30 Gb/s is measured for each channel with good eye diagram and low bit error rate, and hence, a total 1.35-Tb/s data rate can be achieved with the proposed $15 \times 3$ channel SICL array.

Research on Temperature Characteristic of Coaxial Cable Under the Condition of Repetitious Pulse High Current

Pulsed power supply connects energy-dissipation devices by coaxial cable. The temperature of coaxial cable used for repetitious discharge of pulsed power supply can rise highly. This paper focuses on the transient temperature characteristic of coaxial cable under the condition of repetitious pulse high current. In consideration of time and resource consuming of the general 3-D simulation software, 1-D thermal network differential equations (TNDEs) are introduced. In addition, the Arnoldi process is applied to reduce TNDEs’ complexity due to dense space discretization. For model validation and verification, a statistical design of experiments over the parameters of discharge period and current level is organized. The trends of transient temperature around the coaxial cable surface and outer conductor during discharging and cooling process are measured. The experimental results have a good agreement with calculation results. The comparison results show that the theoretical analysis is suitable for analyzing the coaxial cable temperature with different running conditions.

Coaxial Connector Conversion Method for Traceable Scattering Parameter Measurement

This paper reports a connector conversion technique for coaxial lines in the frequency range from 9 kHz to 100 MHz. We designed and fabricated an original connector conversion adaptor, which is composed of an inner conductor and an outer conductor without insulator beads. The scattering parameter of the adaptor was theoretically calculated from the dimensional measurement data, and the expanded uncertainties were propagated from the dimensional measurements, electrical measurements, and configuration of the inner and outer conductors. The method is traceable to the length standard. A measurement to validate the method was performed using a 7 mm to 3.5 mm connector conversion adaptor because these two metrology standards have already been developed in Japan. We confirmed the validity of the proposed method in the frequency range from 9 kHz to 100 MHz.

Development of Semi-Rigid Superconducting Coaxial Cables as Low-Pass Filters

We developed thin semi-rigid coaxial cables for use as readout noise filters in low temperature experiments. The cables reported here had an outer diameter of 0.86 mm, and consisted of a standard cupronickel (CuNi) alloy as a seamless outer conductor and polytetrafluoroethylene (PTFE) as a dielectric material. The inner conductor was superconducting niobium-titanium (NbTi) covered by a CuNi cladding layer with a thickness of 0, 13, or 38 μm. The thermal conductance and transmission properties for the cables were measured at cryogenic temperatures and compared to those for a conventional CuNi semi-rigid cable. Between 1.4 and 8.4 K, the thermal conductance was similar to that for the conventional cable because the contribution from the cladding was estimated to be small. On the other hand, measured at about 3 K, the attenuation at high frequency up to 10 GHz differed in that the cutoff frequency increased with decreasing CuNi cladding thickness. For a cladding thickness of 38 μm, the 3 dB cutoff frequency for a 1-m-long cable was 100 MHz, whereas for a cladding thickness of 13 μm, it was 500 MHz. This type of semi-rigid cable can, therefore, be used as a low-pass filter whose attenuation characteristics can be tailored by changing the thickness of the cladding layer.

Investigation on cold and hot cavity characteristics of overmoded coaxial SWSs with inner corrugations designed for TM02 mode operation at 60 GHz

Coaxial O-type Cerenkov devices usually operate in the quasi-TEM or TM01 mode, but for the purpose of operating at 60 GHz, the coaxial slow-wave structures (SWSs) operating in the TM02 mode were investigated in this paper. To elucidate the working mechanism of coaxial SWSs in the TM02 mode, the cold and hot cavity characteristics are analyzed by numerical calculations. The analysis results suggest that the long periodic length and the short distance between the inner and outer conductors can be adopted to make the group velocity of the TM02 mode at the intersection point close to zero and guarantee single-mode operation. In addition, SWSs with these geometry parameters can achieve high power capacity and high wave-beam interaction conversion efficiency. The starting current is low and the temporal growth is close to the low order modes.

A high-efficiency tunable TEM-TE11 mode converter for high-power microwave applications

The tunable high power microwave source (HPM’s) is considered to be an important research direction. However, the corresponding mode converter has been researched little. In this paper, a high-efficiency tunable mode converter (HETMC) is investigated for high-power microwave applications. The HETMC that is consisted of coaxial inner and outer conductors, with four metal plates arranged radially, at 90° in the coaxial gap, and matching rods can transform coaxial transverse electromagnetic (TEM) mode to TE11 coaxial waveguide mode. The results show that adjusting the length of the downstream plate, and the distance between the rods installed upstream and the closest edges of the plates, can improve the conversion efficiency and bandwidth remarkably. Moreover, when the frequency ranges from 1.63 GHz to 2.12 GHz, the conversion efficiency is above 95% between 1.63 GHz and 2.12 GHz with a bandwidth of 26.1%. Besides, the unwished reflection and transmission can be eliminated effectively in the HETMC.

An L-band transit-time oscillator with mechanical frequency tunability

An L-band coaxial Transit-time Oscillator (TTO) with mechanical frequency tunability is introduced in this paper. Particle-in-cell simulations have been done. The output power efficiency has been improved at least 20% under a 10.2 GW input power and with a tunable range from 1.57 GHz to 1.90 GHz by modulating the outer conductor. It is worth to note that the efficiency can reach as high as 41% at 1.75 GHz. The mechanical engineering method is also detailed in this work. The frequency tuning range of the coaxial TTO is 22.6% of the central frequency. On the other hand, the frequency can be tuned from 1.6 GHz to 1.85 GHz by modulating the inner conductor. The author highlights a hollow structure of the L-band coaxial TTO which can work from 1.03 GHz to 1.31 GHz via modulating the outer conductor in the rest of the article. The frequency tuning range of the hollow TTO is 21.4% of the central frequency. More importantly, the hollow TTO can be easily achieved after the inner conductor is removed from the coaxial TTO. The electric field distributions of the coaxial and hollow TTOs are analyzed, resulting in that the longitudinal and transverse working modes are TM01 and π mode, respectively. The same working mode from these two structures implies the stability of the TTOs mentioned above.

Truncated Circular Cone Slot Antenna Array That Radiates a Circularly Polarized Conical Beam

A truncated circular cone slot array antenna that radiates a circularly polarized (CP) conical beam is presented. The direction into which the conical beam radiates depends mainly on the tilt angle of the outer conductor as well as the proper arrangement of the positions of its two slot arrays. The CP property is realized by introducing quasi-perpendicular slots that are cut into the outer conductor of a truncated circular cone. To illustrate the performance characteristics of this CP conical beam antenna, the tilt angle is set to 45° and the beam angle is pointed at 45° from boresight within the operating band. A prototype was fabricated and tested. The measured results demonstrate that its −10 dB impedance bandwidth ( $\vert S_{{11}}{\rm{\vert \, dB) is 720 MHz, from 5.05 to 5.77 GHz; and its 3 dB axial-ratio (AR) bandwidth is 500 MHz, from 5.5 to 6.0 GHz. Its realized gain over this AR bandwidth ranges from 4.84 to 5.8 dB. The designed beam direction can be easily changed to meet specific application requirements. Moreover, it can be readily reconfigured to be a conformal antenna mounted on the top of a high-speed mobile platform.