Choke Structure Research Articles

Fabrication and high-power testing of an X-band high-power phase shifter for the very compact inverse Compton scattering gamma-ray source.

This paper proposed an X-band phase shifter for the very compact inverse Compton scattering gamma-ray source program at Tsinghua University and conducted its structure design, numerical simulation, fabrication, cold test, and high-power testing. This phase shifter is composed of a polarizer, circular waveguide, and a piston with a choke structure. The simulation results show that the reflection coefficient of the phase shifter is under -40 dB and the insertion coefficient exceeds -0.06 dB at the operating frequency of 11.424GHz. The phase variation is 20°/mm, and a linear phase change from 0° to 360° can be achieved with a piston displacement of 18mm. The manufactured phase shifter has exhibited good performance in the cold test by using the vector network analyzer. After 16h conditioning in the Tsinghua X-band high-power test stand, the phase shifter reached a peak power of 72MW at 230ns pulse width and a peak power of 82MW at 130ns pulse width. After processing signals from the high-speed oscilloscope, it was found that the transmission phase variations were in good agreement with the simulation results.

실험계획법을 이용한 마이크로파 차폐용 개폐도어부의 최적설계

In the heating and drying system using microwaves, an optimal design method was presented to effectively shield microwaves leakage between the door and the cylindrical applicator. In order to protect the human body from leaking microwaves, it is necessary to keep the intensity of microwaves below 5 mW/cm². The door part adopts a choke structure and includes a number of design factors, such as, fin shape, slit shape, and a gap between the applicator and the door. The geometry was optimized by design of experiments, applying full factorial design and response surface method in a 4-factor, 2-level design. The results obtained by ANSYS HFSS analysis were applied to the intensity of microwave leakage according to the change of the design factors. The shape of the choke structure was optimized using Minitab, a statistical program. The microwave heating and drying system was manufactured based on optimal design value and the leakage of microwaves between the door and the applicator was measured. We confirmed that the experimental values were consistent with the simulation values.

Airborne ultrasound pulse amplification based on acoustic resonance switching

Airborne ultrasound radiation pressure, a nonlinear effect that appears as a static force in mid-air in the presence of strong ultrasound, has recently been applied in novel scientific and industrial fields. However, the output power of an ultrasound transducer remains low mainly due to the significant mismatch in acoustic impedance between a solid diaphragm and air. To circumvent this fundamental challenge, we propose to emit amplified airborne ultrasound pulses by instantaneously releasing stored acoustic energy into free-space. Specifically, we implement an acoustic cavity with a mechanically rotating shutter covering its open top. Once the acoustic cavity is fully charged, the stored energy is released by opening the shutter. By developing a choke structure that reduces leakage of the stored energy, we generate ultrasound pulses with 2.5 times higher peak power than the input continuous waves at 40 kHz. This preliminary result has a great potential to generate high-power ultrasound pulses using a conventional air-coupled transducer by separating the storage and radiation process, thus circumventing the fundamental limitation brought by impedance mismatch.

Editorial: Plasmonic metamaterials and electromagnetic devices volume 2

In parallel to communication systems, electromagnetic devices also play a vital role in many fields such as radar and security equipment. Due to the power capacity limitation of the rotary joint, mechanical scanning radars are limited to use high-power microwave sources to improve their performance furthermore. Zhang et al. introduced an over-mode circular waveguide rotary joint with radial mutations at the rotation point to solve this problem. The structure is optimized to suppress unwanted modes. By connecting the choke slot and the rotating part, the breakdown risks of the rotary joint can be reduced. In addition, the choke structure is connected to the inner wall of the waveguide with a gap, the normal modes inside the waveguide will not be affected by the breakdown. This Research Topic contains 3 articles devoted to the recent progress in electromagnetic devices. Much more efforts are still ongoing in this fascinating area.

Fan-Out Antenna-in-Package Integration Using Heatsink Antenna

Antenna-in-package (AiP) has been widely applied for millimeter wave system integration. Fan-out interconnection provides low parasitic parameters and is the most suitable technology for monolithic microwave integrated circuit (MMIC) packaging. Thermal design should be considered due to high power consumption of mm-wave chips. For compact AiP system, arrangement of heat sink should not influence radiation performance. In this work, an AiP topology is proposed using 3-D fan-out integration, miniature horn antenna is adopted as heat sink with relative high gain and wide band. A small sized organic substrate board is embedded in molding compound for right-angle transition of millimeter wave signal. Choke structure is designed at the bottom surface of metal horn with improved transition performance. Two horn antennas are designed with measured gain 11.5 and 15.4 dB, respectively, bandwidth under return loss −10 dB is higher than 16.7% for 60 GHz wireless communication. The AiP system has been manufactured and measured on test board with well-functioned radiation performance. Thermal dissipation model is analyzed, measured results under 340 mW power consumption are consistent with simulation.

A High-Power Radar Rotary Joint

Due to the power capacity limitation of the rotary joint, mechanical scanning radars are limited to use high-power microwave sources to improve their performance furthermore. To solve this problem, an over-mode circular waveguide rotary joint with radial mutations at the rotation point is introduced in this letter. The structure of the radial mutation is optimized to suppress unwanted modes. By connecting the choke slot and the rotating part, the breakdown risks of the rotary joint can be reduced. In addition, the choke structure is connected to the inner wall of the waveguide with a gap, even the breakdown occurs in the choke, the normal modes inside the waveguide will not be affected. To verify the design, a prototype of the rotary joint is fabricated and measured with the operating band in the range of 9.5–10.5 GHz and a power capacity of 3 GW.

Wideband End-Wall Transition From Microstrip to Waveguide With via-Less Choke Structure for Terahertz Application

In the end-wall transition from planar lines to waveguide, the via holes are generally arranged around the waveguide port to prevent power leakage, which increases production cost and manufacturing errors in terahertz band. In this letter, a novel wideband transition from microstrip to waveguide with via-less choke structure is proposed. A simple rectangular patch is utilized to convert the quasi-TEM mode of microstrip line to the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode of waveguide. In place of the via holes, multiple open stubs are introduced to suppress the power leakage. Furthermore, an extra resonant mode is generated by controlling the length of open stubs, which leads to a wider working band. Two back-to-back prototypes with different lengths are designed and fabricated over 300 GHz. The simulated and measured results are in good agreement. The measured return loss of single transition is better than 12 dB with an insertion loss of 0.9 ± 0.11 dB in the range of 314–369 GHz (16.1% bandwidth).

Sleeve Monopole Antenna With Choke Structure for Broadband Application

A new type of sleeve monopole antenna with a choke structure for broadband applications is proposed in this letter. The antenna consists of a choke structure and a single-sleeve structure, which effectively broadens its impedance bandwidth. Meanwhile, the top-loading technique is applied to reduce the size. The proposed structure is designed, analyzed, and optimized. Parameters study is carried out for its working mechanism. The fabricated antenna is measured, and the measured results have good agreement with the simulated ones. The antenna shows the omnidirectional radiation with a broad impedance bandwidth ranging from 0.24 to 0.95 GHz. The proposed antenna has a potential application in wireless communication.

In situ annealing of photocathodes using backside electron-beam irradiation

Metal and metal-compound photocathodes are generally used as electron sources in radio frequency (RF) guns. These photocathodes are robust against laser irradiation and RF fields, are easy to handle, and have longevity. The surface cleaning of photocathodes is essential to improve and maintain their quantum efficiency (QE) in an RF gun cavity. In this paper, we propose a backside electron-beam irradiation heating technique as an in situ surface-cleaning procedure for photocathodes in an RF gun cavity. In the proposed technique, thermal electrons accelerated by a DC electric field are irradiated from the back of the photocathode, and their beam power is converted to heat, thereby heating the photocathode. Unlike other surface-cleaning techniques, surfaces of any cathode shape can be cleaned uniformly using this heating method. We designed and developed a cathode plug that includes the proposed heating system for large-diameter (~8 mm) photocathodes. Thermal simulation of the entire system, including the photocathode and its holding structure, and RF simulation of the choke structure for preventing the leakage of RF power were performed. The developed heating system was installed in an RF gun in High Energy Accelerator Research Organization KEK and subjected to RF aging and beam commissioning. From the results of beam commissioning, it was found that the QE of the photocathode increased to approximately 2.5 times the initial value due to the in situ annealing in the RF gun cavity.

Coaxially Fed Antenna Composed of Monopole and Choke Structure Using Two Different Configurations of Composite Right/Left-Handed Coaxial Lines

Coaxially Fed Antenna Composed of Monopole and Choke Structure Using Two Different Configurations of Composite Right/Left-Handed Coaxial Lines

낮은 정재파비와 삽입손실을 갖는 밀리미터파(Ka 밴드) 복합모드 탐색기용 2-축 도파관 로터리 조인트 설계 및 제작

In this study, a Ka-band waveguide rotary joint that can be applied to a millimeter-wave seeker is designed and fabricated. The proposed rotary joint maintains a low standing-wave ratio and low-loss characteristics, and has two rotary axes designed to enable azimuth and elevation rotation. The rotary joint is designed as a ridge-waveguide-type mode converter and a λ/4 choke structure to match the electromagnetic wave propagation mode between the spherical and circular waveguides. A performance test using a network analyzer and a high-power transmitter to assess vibration and shock were conducted. Results showed that the rotary joint had a very low standing-wave ratio of less than the maximum of 1.19:1 and an insertion loss of less than 0.80 dB at Fc±500 MHz.

Bandwidth Extension of Planar Microstrip-to-Waveguide Transition by Controlling Transmission Modes Through Via-Hole Positioning in Millimeter-Wave Band

This paper presents a design technique to achieve a broadband planar microstrip-to-waveguide transition in a millimeter-wave (mmWave) band. In the conventional planar microstrip-to-waveguide transition, via holes are located around the rectangular waveguide and microstrip line to prevent power leakage due to the generation of a multi-transmission mode. Therefore, a single-transmission mode is dominant at the input port of the transition, with a narrow bandwidth of the single resonance. In the broadband planar microstrip-to-waveguide transition, via-hole positioning is utilized to add inductance to constrain the predominance of the single-transmission mode at the input port of the transition. The double-resonant frequency yielded by excitation of the grounded coplanar waveguide transmission mode and parallel plate transmission mode is obtained by controlling the positions of holes adjacent to the microstrip line. Moreover, to simplify the structure and meet the requirement of high assembly accuracy in fabrication, two holes adjacent to the microstrip line are maintained, but the remaining holes are replaced by a choke structure that performs the equivalent function to the via-hole arrangement. The influences of the multi-transmission mode and choke structure on the characteristics are investigated by electromagnetic analysis, and the feasibility is confirmed by experiments in this work. A double-resonant frequency and a broad bandwidth of 10.6 GHz (13.8%) are obtained. The measured results of the broadband planar microstrip-to-waveguide transition using via-hole positioning show an insertion loss of 0.41 dB at the center frequency of 76.5 GHz.

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.

Design of absorptive frequency selective surface with good transmission at high frequency

An absorptive frequency selective surface with a wide absorptive property over the low band and a good transmissive property at high frequency is designed. The transmission of high frequency is realised by putting a choke structure into the element to control the current distribution. Its −10 dB absorption band is from 2.8 to 8.3 GHz and the transmission band is at 9.7 GHz with insertion loss <0.5 dB. Numerical and experimental results are given.

Demountable damped cavity for HOM-damping in ILC superconducting accelerating cavities

We have designed a new higher-order-mode (HOM) damper called a demountable damped cavity (DDC) as part of the R&D efforts for the superconducting cavity of the International Linear Collider (ILC). The DDC has two design concepts. The first is an axially symmetrical layout to obtain high damping efficiency. The DDC has a coaxial structure along the beam axis to realize strong coupling with HOMs. HOMs are damped by an RF absorber at the end of the coaxial waveguide and the accelerating mode is reflected by a choke filter mounted at the entrance of the coaxial waveguide. The second design concept is a demountable structure to facilitate cleaning, in order to suppress the Q-slope problem in a high field. A single-cell cavity with the DDC was fabricated to test four performance parameters. The first was frequency matching between the accelerating cavity and the choke filter. Since the bandwidth of the resonance frequency in a superconducting cavity is very narrow, there is a possibility that the accelerating field will leak to the RF absorber because of thermal shrinkage. The design bandwidth of the choke filter is 25kHz. It was demonstrated that frequency matching adjusted at room temperature could be successfully maintained at 2K. The second parameter was the performance of the demountable structure. At the joint, the magnetic field is 1/6 of the maximum field in the accelerating cavity. Ultimately, the accelerating field reached 19MV/m and Q0 was 1.5×1010 with a knife-edge shape. The third parameter was field emission and multipacting. Although the choke structure has numerous parallel surfaces that are susceptible to the multipacting problem, it was found that neither field emission nor multipacting presented problems in both an experiment and simulation. The final parameter was the Q values of the HOM. The RF absorber adopted in the system is a Ni–Zn ferrite type. The RF absorber shape was designed based on the measurement data of permittivity and permeability at 77K. The Q values of the HOM in the DDC are 10–100 times lower than those of a TESLA-type HOM coupler.

A Waveguide Design of Microwave High Power Passive Tuner

Passive tuner is the core component of high-power load pull measurement system. To overcome the leakage of electromagnetic field to the outer space and decrease the insertion loss, a structure of waveguide and diaphragm with the choke structure is adopted to design the 25-40GHz tuner. The simulation results of HFSS (High Frequency Simulator Structure) software show that the structure can meet the requirements of the tuning ratio and decrease the insertion loss, and it can be used in the load and source pull measurement system successfully.

Transmit–Receive Isolation Improvement of Antenna Arrays by Using EBG Structures

The mushroom-like electromagnetic band-gap (EBG) structure combined with a choke structure is applied to improve the transmit-receive (T/R) isolation of two X-band large antenna arrays. The basic idea presented is to suppress the surface wave propagation between the T/R arrays by utilizing EBG walls formed through a vertical configuration of the EBG cells, so as to improve the T/R isolation. The isolation level of the arrays with the EBG walls and a metal choke is measured and compared to other isolation methods applied. The experimental results show that by using this combined structure, the isolation level can be improved by at least 30 dB in the radar's operation band, which shows its high efficiency.

Numerical Calculation of Throttle Nozzle Diameter Influence on Downhole Choke Flow Field

With calculation results comparison of different throttle nozzle diameter value, This article analyses the flow field with throttle nozzle diameter variety of 1.0mm, 2.0mm, 2.4mm, 2.6mm, 2.8mm, 4.0mm, while the other parameters take same value (such as the inlet pressure is 20mpa, the outlet pressure is 10MPa, the temperature is 333k, and the well depth is about 2000m). the results present the influence upon downhole choke flow field including pressure, velocity, temperature distribution. The pressure field composed by minimum on the axis shows the pressure dropping change at the throttle nozzle outlet. Velocity field gives the maximum value of velocity and Mach number, which determines the flow field is subsonic or supersonic flow. With hydrate formation conditions, temperature field formed by minimum on the axis gives the existing judgment of hydrate formation under a certain condition. With the throttle nozzle diameter increasing, the outlet flow maximum velocity increases, and the differential pressure before and after nozzle becomes larger, which means the pressure drop effect is better. The downhole choke design of throttle nozzle needs to consider the combination effects of pressure drop and temperature drop. These parameters provide reference for downhole choke structure design and operating performance improvement.

Simulation Investigation of L-Band Ladder Cathode MILO

For the sake of higher power conversion efficiency, optimization for L-band ladder cathode magnetically insulated line oscillator (MILO) based on an existing model by numerical simulation is carried out. First, the efficiency is improved by changing the parameters of choke and slow-wave structure vanes. The resonant frequency and Q factor are obtained through numerical calculation of open cavity high-frequency characteristics. Then, a 2.5-D electromagnetic PIC code is used for optimizing simulation. Employing an electron beam of 568 kV, 53.3 kA, a TEM mode high-power microwave with output power of 5.5 GW, frequency of 1.2 GHz is obtained. The power conversion efficiency is 18.2%. A novel four-cavity ladder cathode MILO is also presented which is more compact and also has high-power conversion efficiency. The typical simulation result is as follows: Employing an electron beam of 578 kV, 46.5 kA, a TEM mode high-power microwave with output power of 5.1 GW, frequency of 1.2 GHz is obtained. The power conversion efficiency is 18.9%.

Compton scattering monochromatic X-ray source based on X-band multi-bunch linac at the University of Tokyo

We are currently developing a compact monochromatic X-ray source based on laser–electron Compton scattering for the purpose of medical applications at the University of Tokyo. To realize remarkably compact-, high-intensity- and highly stable system, we adopt an X-band (11.424 GHz) multi-bunch linear accelerator (linac) and reliable Q-switch Nd:YAG laser. The injector of the system consists of a 3.5-cell X-band thermionic cathode RF-gun and an alpha magnet. So far, we have continued high-power experiment and beam generation on X-band thermionic cathode RF-gun. However, breakdown was frequently occurred at coaxial structure around the thermionic cathode. In order to resolve the breakdown, we adopt a choke structure around the thermionic cathode. In this paper, the details of Compton scattering X-ray source the University of Tokyo, the experimental results of the X-ray generation, and upgrade of the X-band thermionic cathode RF-gun will be presented.