Dual Directional Coupler Research Articles

An H-Plane High-Flatness Ridge Waveguide Dual-Directional Coupler Based on Copper Additive Manufacturing

An <i>H</i>-Plane High-Flatness Ridge Waveguide Dual-Directional Coupler Based on Copper Additive Manufacturing

Non-intrusive measurements of plasma impedance in an electron-cyclotron resonance thruster

We present a general method allowing for direct measurements of the complex impedance of radio frequency devices that need to be powered by an external power supply unit, making use of a dual-directional coupler and a vector network analyzer. This method is used to measure the impedance of an operating electron-cyclotron resonance thruster, which is then calibrated using a custom triple-short calibration kit to retrieve the impedance of the plasma within the chamber. The measurements, realized without disturbing the thruster operation, show that the plasma impedance ranges between 55 and 90 Ω in resistance and between −30 and 20 Ω in reactance. An equivalent circuit model is finally discussed, aiming at estimating plasma parameters through these impedance measurements.

Development and testing of 37.8 MHz, 3.0 kW RF amplifier system for Radioactive Ion Beam facility at VECC Kolkata

This paper reports the design, development and testing of a 3.0 kW, 37.8 MHz radio frequency (RF) amplifier system that has been built by combining four solid-state amplifier modules of 1.0 kW each. The design philosophy and test results of individual components such as driver amplifier, final amplifier modules, power divider/combiner, dual directional coupler (DDC) with system control and interlocks are discussed in detail. Compact 4-way Wilkinson power divider and combiner have been implemented using combination of 50 Ω coaxial cables at this lower frequency of 37.8 MHz. It provides better isolation between the ports and also have high power handling capability. The amplifier has been tested with existing 37.8 MHz quarter-wave resonator type re buncher in the Radioactive Ion Beam (RIB) facility. The performance test results of developed RF system with Re buncher cavity have been presented in this report.

Investigation of RF driver equivalent impedance in the inductively coupled SPIDER ion source

SPIDER experiment includes an RF inductively coupled plasma source working at 0.3 Pa of gas pressure (H/D) where plasma is generated and heated by eight RF drivers, fed by four RF circuits. A single RF circuit is composed of two drivers connected in series, attached to a capacitive matching network, fed by 200 kW 1 MHz RF oscillator through a coaxial transmission line. The knowledge of driver impedance in different experimental conditions is a valuable window for understanding the characteristics of generated plasma. Direct measurement of driver impedance in SPIDER is not possible, it has been estimated via the development of a suitable electrical model of the RF circuit using as input, measurements at the oscillator’s output. This paper reports on the progress in the modeling of the SPIDER RF circuit and discusses a procedure to estimate the driver impedance exploiting also the recently available experimental measurements from the dual directional coupler. The impedance obtained with this approach, derived from measurements obtained in a recent SPIDER campaign, is reported for various operating conditions, such as RF power, gas pressure, plasma grid current, cesium injection rate, type of gas (hydrogen and deuterium), etc.

A Real-Time Energy Monitoring System for an MRI Hybrid Ablation System.

The MRI hybrid ablation system is an approach to use the MR (magnetic resonance) scanner's radiofrequency amplifier itself as power source for ablation. Hereby, an electrode is connected to the MR internal radiofrequency amplifier. An average RF power is provided through a train of short RF pulses, which is sufficient to thermally destroy tissue. However, ablation with too high power values can cause tissue carbonizations, thus impeding the ablation procedure. Therefore, monitoring of the energy and the power absorbed inside the tissue is necessary. For this purpose, a measurement system was designed to measure the energy applied to the tissue when using the concept of an MRI hybrid ablation system. The system consists of a dual-directional coupler, RF-to-RMS sensors, and a microcontroller. The gradient calculation of the measured energy curve provides information about the absorbed RF power in the tissue. Validation measurements of the system were performed and compared with measurements from the MR-internal power measurement system. The energy monitoring system was also tested in an ablation experiment with ex-vivo animal tissue using the MRI hybrid ablation system. The measurements showed that the applied RF power can be monitored in real-time. It has been shown that the mean RF power absorbed in the patient decreased during an ablation procedure due to an occurring impedance mismatch and tissue changes. In further work, the influence of the monitoring system on the quality of the MR images should be investigated. Clinical relevance- This paper demonstrates an energy monitoring system for an RF ablation system, which can be used inside an MR environment.

Design process for dual coplanar waveguide directional couplers for power transmission

In this paper, a design process for power directional couplers using dual conductor-backed coplanar waveguides (CBCPW), is presented. The proposed methodology is applied to the design of a 50 Ω impedance coupler with 10 dB coupling factor for a central frequency of 2.5 GHz. The resulting coupler is validated through simulation by obtaining its dispersion parameters using ANSYS High Frequency Structure Simulator (HFSS). From the analysis of the return loss, insertion loss and coupling factor, in a range of 1 to 4 GHz, it was found that the coupling factor complies with the design specification for frequencies from 2 to 3 GHz, with insertion losses between -1 and -2 dB around the center frequency and return losses of -15 dB.

Logic gates through three core and dual core nonlinear directional couplers operating in continuous wave mode

Logic gates through three core and dual core nonlinear directional couplers operating in continuous wave mode

Novel Methodology to Assess RF Performance of Co-located MIMO Radar Systems Transmitting Binary Phased Coded Waveforms

In this work an experimental radar testbed and dual directional couplers (DDC) are used to collect measurements of the forward and reverse waves at each element, its mutual coupling, and beam-patterns. The collected measured data is used to validate a methodology for assessing radio frequency (RF) performance of a co-located multiple-input multipleoutput (MIMO) radar system transmitting binary phased coded (BP) waveforms. The estimated and measured active reflection coefficient (ARC) and beam-patterns are presented. The effect of different excitations and mutual coupling on the radiated fields is also presented.

Systematic and Random Errors in the Net Power Measurement Using a Reflectometer

Net power delivered to a device is one of the important quantities to obtain various free field parameters in the radio frequency band, such as electric field strength, and a reflectometer is one practical choice for the real-time net power measurement. In carrying out the net power measurement, a pair of reflectometer calibration coefficients obtained by assuming the coupler idealities is used to estimate the forward and reverse traveling powers at the test port. In this article, the systematic and random errors of the measured net power by using the reflectometer are thoroughly discussed in terms of the terminal condition at the test port. In addition, useful parameters to evaluate the quality of the dual-directional coupler as a component of the reflectometer are proposed.

A novel ex situ diagnostic technique for characterizing harmonics in radio frequency discharges.

An accurate, non-invasive ex situ diagnostic technique for analyzing plasma generated harmonics in radio frequency (RF) discharges is presented utilizing a broadband Dual Directional Coupler (DDC) that measures accurately both forward and reflected voltage signals in a transmission line. For usual applications such as monitoring forward and reflected power, the DDC is placed between the RF generator and the matching network (MN). However, the MN reflects all plasma generated harmonics back toward the plasma. Hence, no harmonics reach the generator side of the MN. Thus, for monitoring the harmonics, it is necessary to place the DDC between the impedance matching unit and the plasma, which was used for the first time in an asymmetric, parallel plate RF discharge at 13.56 MHz, 10 W-50 W at 200 mTorr (argon). The analysis of DDC data yields voltage, harmonic power contents, complex load impedance, plasma reflection coefficient, Voltage Standing Wave Ratio (VSWR), etc., for the fundamental frequency. For instance, at 10 W net input power, the computed plasma impedance is ZL = Rp + jXp, with Rp = 16.8 Ω and Xp = -81.9 Ω, yielding VSWR ≈11. Additionally, for 50 W input power, the third harmonic (72.31 mW) is dominant, followed by the second (8.28 mW) and fourth harmonics. In contrast, the literature states that the second harmonic is usually dominant, possibly due to the invasive nature of the diagnostics. Because harmonics are an important signature of processes taking place within the plasma, the proposed diagnostic can be effectively used for calibration and verification of theoretical models/simulations for resolving relevant physics issues.

Design of WPT RF Power Supply Based on Dual Directional Coupler and Capacitor Array Impedance Matching Network

In the engineering use of a magnetically coupled resonant radio energy transmission system, both the resonant frequency and the optimal load impedance will be varied because of the external conditions. In view of the above problems, this paper proposes an RF power supply with adjustable frequency and optimal load impedance, in order to achieve efficient power transmission for different frequency radio energy transmission systems and different load conditions. The RF power supply is mainly composed of a frequency controllable signal generator, a Class E power amplifier circuit, a dynamic impedance matching network, a load detection circuit and a controller. Through the above parts, the load tracking of the RF power supply can be realized, and the higher output efficiency can be realized under the condition of changing the working frequency and the load. Finally, the feasibility of the proposed RF power supply is verified through experiments. The experimental results show that the RF power supply can automatically track changes in the operating frequency and load range, and the output efficiency can be maintained at more than 75%.

Design and development of high power variable dual‐directional radio frequency coupler

Design and development of coaxial line-based 10–40 dB variable loop type dual-directional coupler for the frequency range of 50–500 MHz for 2 kW power handling capability has been presented in this study. The directional coupler has to be used in the radio frequency plasma experiment to detect the reflected power, so as to safeguard the system from unwanted reflected power. It consists of a main coaxial transmission line with two similar movable loop type coupling arrangements. The movable loops provide variable coupling for forward and reflected power separately, where the magnitude of coupling can be selected independently both for forward and reflected wave. The developed coupler has been tested where test results show return loss and isolation better than −10 dB and coupling from − 10 to − 40 dB in the frequency range of 50–500 MHz.

Design of all-optical AND logic gate at 20 Gb/s based on SOA-MI with optimum injection current and length of TWA-SOA

The manuscript presents Design of All-optical AND logic gate at 20 Gb/s using Semiconductor Optical Amplifier based on Michelson Interferometer (SOA-MI). The paper shows a comprehensive numerical simulation using OptiSystem software to examine two-input logical function (with 8-bit). Used the CW Laser, Dual Directional Coupler, 100% reflective linear Fiber Bragg Grating (FBG) and Optical Filter, and investigated the optimum injection current and length of the TWA-SOA for obtaining the best result Q-Factor and BER based on Eye diagram to logic gate. To the best of our knowledge, this is the first report on a numerical simulation of an All-Optical AND logic gate at 20 Gb/s with SOA-MI using co-propagating, structure with results ensure good performance of the proposed design.

A Multiband Directional Coupler Using SOI CMOS for RF Front-End Applications

This letter introduces a novel multiband directional coupler for RF front-end applications. Conventional narrowband directional couplers are widely used for mobile applications because of their compact size. However, excessive power loss due to strong coupling in the higher frequency range severely limits their bandwidth. To resolve this issue, we propose a dual directional coupler employing a coupling switching stage, where the asymmetric coupled lines can be electrically coupled or floated to mitigate severe coupling loss. The proposed coupler has been implemented to an integrated circuit using the silicon-on-insulator process. The measured results showed a considerably enhanced bandwidth from 0.69 to 4 GHz covering the entire frequency band of long-term evolution with a low power loss of less than −0.21 dB in the target frequency range.

Acoustic Vector-Corrected Impedance Meter

We describe the development of a novel instrument intended for the measurement of the acoustical reflection coefficient of materials. The instrument effectively implements a one-port vector-corrected network analyzer in the acoustic, rather than the electromagnetic, domain. Employing the well-documented methods of error correction familiar to microwave engineers, this instrument permits automated measurement of an acoustic impedance presented to a waveguide port. A dual-directional coupler allows a working frequency range of well over an octave. In principle, a set of six couplers would allow measurement from 100 to 50000 Hz.

Calibrating Dual-Directional Couplers and Evaluating Uncertainties in Net Power Delivery

Dual-directional couplers are used to monitor net power fed into transmitting antennas in standard-field systems at NIM, China. It is essential to calibrate the coupler and evaluate the measurement uncertainty in the net power in such applications. The method we use at NIM to calibrate couplers are presented in this paper, and a complete model that takes into account the measurement uncertainties of couplers and horns to evaluate uncertainties in net power delivery is proposed. A case study is also provided of power delivery by a coupler with the nominal directivity of 40 dB using the Monte Carlo analysis based on the complete model and actual measured data.

Performance and Probe Measurements of a Radio-Frequency Plasma Thruster

The performance of a radio-frequency plasma thruster is evaluated using a displacement-type, inverted-pendulum thrust stand in the Large Vacuum Test Facility at the University of Michigan. A radio-frequency generator supplies up to 2000 W to the radio-frequency plasma thruster at a fixed frequency of 13.56 MHz. The matching network is placed inside the vacuum chamber at the thruster, and the radio-frequency power is measured at the matching network input port with a dual-directional coupler. A Faraday probe measures the current density in the far-field exhaust of the thruster, a retarding potential analyzer characterizes the ion voltage distribution, and a Langmuir probe measures the plasma potential. The radio-frequency plasma thruster is operated with argon propellant at mass flow rates of , at corresponding corrected facility pressures of . The maximum thrust observed is 10.8 mN, and the maximum specific impulse is 303 s. Thrust efficiency is below 1% at all conditions. Faraday probe results show that the propellant utilization efficiency is below 15% and that the ionized exhaust has an effective divergence half-angle of 48 deg. Thrust is negatively correlated with the ion beam most probable voltage, showing that retarding potential analyzer results alone may not accurately characterize thruster performance. Charge-exchange collisions likely have a significant influence on radio-frequency plasma thruster operation.

Analysis of the Performance of Optical Code-Division Multiple-Access System (OCDMA), Operating with Gold Codes under Nonlinear Effects

A numerical simulation study of the performance of encoding and decoding of short optical pulse in OCDMA (Optical Code Division Multiple Access) systems under non-linear optical effects is presented. The performance of encoding and decoding short pulses is obtained through use of device FBG (fiber Bragg grating) where the codes are inserted through discrete jumps in the optical phase (±π). The multiuser interference is also the object of the present study, where a figure of merit (interference figure) is used to quantify the interference in multiuser auto and cross correlation. We evaluate the dependence of the multiuser interference for the coupling constant of FBG. Finally, the interference inserted in the autocorrelation due to nonlinear effects generated in the nonlinear switching of the coded pulse in a dual core nonlinear directional coupler is examined, where temporal broadening of pulses decoded is observed.

Development of microcontroller-based microwave system to measure solid content of hevea rubber latex

This paper describes the development of digital, portable, simple to operator, cheap and accurate microwave instrument to determine the total solid content (TSC) or moisture content (MC) of hevea rubber latex by using microcontroller, dual directional coupler, and open-ended coaxial probe. A low-cost stripline dual directional coupler and open-ended coaxial probe are simulated, designed and connected to microwave source and detectors. TSC parameter is obtained from the relationship between moisture content in the sample and the value of reflection coefficient from coaxial probe. Experimental results are presented and the empirical equation was implemented by the microcontroller for the calibration and followed the calculation setup. The whole system was tested by using diluted rubber latex with different TSCs at room temperature (25°C) and the results of standard oven drying method and this study were found with the accuracy and reproducibility at the level of less than 1%.

Development and commissioning of a test system based on a TEM cell for RF exposure

In the development of a low-cost two-port TEM cell, a new analytical model of the capacitance of the terminations has been performed. The model has been verified by calcula ting the termination capacitance by means of a commercial 3D code. A TEM cell modified in accordance with the obtained results has been tested, with reference to the voltage standing wave ratio (VSWR) parameter, and the obtained improvements on VSWR versus frequency are reported. The TEM cell is the principal part of a test system for RF exposure (up to 230 MHz), including signal generator, power amplifier, dual directional coupler, 50 Ω load attenuator and 1 GHz bandwidth oscilloscope, whose commissioning has been performed. A numerical analysis has been performed also for calculating the stationary electric field in the TEM cell. Experimental measurements of electric field inside the TEM cell, by means of an electric field meter (100 kHz 6 GHz broadband) were done, and the results are in good agreement with the numerical data.