Coaxial Cavity Research Articles

In brief

PAGE 1325 Idle optical and electrical links consume unnecessary power when not in use. Work from Switzerland, the USA and Germany proposes a high-amplitude wake-up pulse for vertical-cavity surface-emitting lasers, which become activated when optical links in data centers are accessed. The high-amplitude pulse results in rapid wake-up times and data access with low power requirements for idle links. PAGE 1316 Researchers in China propose a singly coaxial re-entrant cavity for measuring the dielectric parameters of small samples. The authors measure broadband complex permittivity properties of several samples, which have different shapes and are formed of different materials. The designed cavity offers an increased ease-of-use and sensitivity over existing methods with a wide bandwidth of operational frequencies. A high-amplitude wake-up pulse for idle optical links. PAGE 1318 A symmetrical antipodal Fermi linear tapered slot antenna (AFLTSA) is proposed for Ka frequency band applications in work from Canada. The proposed design consists of four antenna elements with element excitation achieved by a beamforming network rather than the use of couplers or phase-shifters. The antenna has been designed for millimeter wave-based target tracking and imaging systems. Broadband complex permittivity properties measurements are achieved with a new cavity structure. PAGE 1323 The placement of a perimeter gate (PG) in single-photon avalanche diodes (SPAD) prevents premature breakdown under applied voltage. Researchers in the USA have fabricated and simulated multiple PGSPADs with varying physical parameters including, device size, shapes and junction type. The effects of the physical parameters on the breakdown voltage and optical response of the devices are discussed. A new AFLTSA is proposed for millimeter wave-based tracking and imaging systems. PAGE 1300 Work from Iran proposes a modified sensor for permittivity measurements of liquids. The sensor is a planar U-shaped resonator that has been designed with gap sections, coupled lines and central ring resonators to achieve maximum sensitivity for liquid measurements. The authors demonstrate the sensor to offer an increased sensitivity of approximately 45% over existing measurement methods. Designing single-photon avalanche diodes to prevent premature breakdown under applied voltage. A new efficient sensor for measuring the dielectrics properties of liquids.

Properties of quarter-wavelength coaxial cavity for triode-type thermionic RF gun

A quarter-wavelength coaxial cavity with a longitudinal radio-frequency power supply was fabricated and tested. The cavity was designed as a pre-buncher for a thermionic triode-type radio-frequency gun of a mid-infrared free electron laser facility. The triode structure was formed to ensure the reduction of the back-bombarding effect, which usually appears in thermionic radio-frequency guns. The coaxial cavity was tested using a tungsten dispenser cathode. From the results of the cold test, a cavity voltage of about 25 kV can be attained, which corresponds to designed characteristics. In contrast, the hot test showed a sudden drop in voltage, resulting in an unstable operation. The small dimensions of the cavity caused some low-field effects, which led to multipactoring. In this paper, we report the tested characteristics of the pre-bunching cavity.

Simulations of S-band RF gun with RF beam control

The RF gun with RF control is discussed. It is based on the RF triode and two kinds of the cavities. The first cavity is a coaxial cavity with cathode-grid assembly where beam bunches are formed, the second one is an accelerating cavity. The features of such a gun are the following: bunched and relativistic beams in the output of the injector, absence of the back bombarding electrons, low energy spread and short length of the bunches. The scheme of the injector is shown. The electromagnetic field simulation and longitudinal beam dynamics are presented. The possible using of the injector is discussed.

Numerical Research on a 170-GHz Time-Dependent Multimode Coaxial Gyrotron With Outer Corrugation

In this paper, a coaxial gyrotron with outer corrugation is considered. Its multimode electron equation of motion is derived from the Lorentz equation, and its time-dependent amplitude and phase equation for the $\mathrm {TE}_{mn}$ mode is obtained from the wave equation. Using the time-dependent multimode beam–wave interaction equations, the time evolution processes of the time-dependent multimode coaxial cavity gyrotron with outer corrugation are investigated by numerical calculation. Results show that a 170-GHz coaxial gyrotron with outer corrugation can start up and operate stably at the $\mathrm {TE}_{34,19}$ mode and its competing modes are suppressed under different initial field amplitude conditions. By the calculation of the time-dependent multimode and single-mode coaxial gyrotron with outer corrugation, it is found that the output power and the output efficiency of the $\mathrm {TE}_{34,19}$ mode are 1.856 MW and 32.59%, respectively. These studies show the mode competition processes of the coaxial gyrotron with outer corrugation at the beginning start-up stage.

A compact multiple‐way double ring‐cavity power divider

AbstractDesign of an ultra‐wideband multiple‐way power divider based on the coaxial ring cavity configuration is presented. The proposed design includes increased numbers of the power divider ports, compared to the available designs, thanks to an incorporated coaxial power divider. For this purpose, the cavity layer in the ring cavity power divider is designed in two separate cavity rings and each ring is fed independently through an integrated coaxial power divider. Therefore, the number of the output ports is increased by 50%. A sample prototype is simulated for ultra wideband frequency range, and the performance is computed by using a full wave electromagnetic simulation technique. The power divider has 50 ports of 32 outer ring and 18 inner ring ports. The impedance bandwidth for the return loss <15 dB is obtained for the frequency range of 4‐10.5 GHz. The average insertion loss, amplitude imbalance, phase imbalance, and group delay are better than 0.4 dB, ±0.8 dB, 12°, and 0.6 ns, respectively.

Full Wave Analysis of Plasma Loaded Coaxial Gyrotron Cavity With Triangular Corrugations on the Insert

The presence of plasma inside the gyrotron interaction structure alters the mode field. The presence of a magnetic field changes the plasma to an anisotropic media. Field analysis of a plasma loaded coaxial gyrotron cavity with triangular corrugations on the insert is undertaken using full wave approach. Modes inside a plasma loaded interaction structure have all six nonzero field components and hence are hybrid modes. Plasma modes (space charge modes), cyclotron modes, and waveguide EH and HE modes are the three families of modes that can exist in plasma loaded waveguide. Inside the gyrotron interaction structure, the cyclotron mode and the desired mode (HE) couple and this coupling leads to change in the eigenvalue of the modes. In this paper, a full wave approach has been used to analyze the dispersion relation and calculate eigenvalue of the desired HE mode.

Full Wave Analysis of Coaxial Gyrotron Cavity With Triangular Corrugations on the Insert

Field analysis of coaxial gyrotron cavity with triangular corrugations on the insert is undertaken using full wave approach. The inclusion of insert offers the advantage of mode selectivity and reduction in voltage depression. The effect of insert can be enhanced by having corrugations on it. Mathematical expressions for eigenvalue and ohmic loss of triangular corrugated coaxial cavity have been derived using full wave approach specifically space harmonics method (SHM). Degeneration of SHM to surface impedance method under specific conditions is also discussed and analyzed. The inclusion of harmonics has a small effect on eigenvalue but the ohmic loss varies significantly. An interaction structure design for 170-GHz, 2-MW coaxial-cavity gyrotron with triangular corrugations on the insert is discussed. Mode competition and ohmic losses for such a structure have also been calculated.

A 170 GHz time-dependent multi-mode coaxial gyrotron with inner corrugation

In this paper, a time-dependent multi-mode coaxial gyrotron with inner corrugation is introduced. The time-dependent amplitude and phase equation of the mode TEmn and the multi-mode electron motion equation are derived from the wave equation and the Lorentz equation, respectively. Using these equations, the time evolution of the time-dependent multi-mode coaxial cavity gyrotron with inner corrugation is studied by numerical calculations. Researches show that a 170 GHz coaxial gyrotron with inner corrugation can start up and stably operate in the mode TE32,17 and its competition modes are depressed under the given operation parameters. It is found that the output power and the output efficiency of the coaxial gyrotron with inner corrugation are 2.205 MW and 40%, respectively. These studies display the mode competition process of the time-dependent multi-mode coaxial gyrotron with inner corrugation. It is helpful to further research on the beam-wave interaction of the gyrotron.

Generalised direct matrix synthesis approach for lossless filters

A generalised direct matrix synthesis is proposed for microwave lossless filters with arbitrary phase shift at centre frequency and complex terminal impedances. The functions of traditional lossless filters, ideal phase shifters, and ideal impedance matching networks are thus substantially combined into one entity to provide an attractive technique for the realisation of compact narrowband microwave front-ends. The synthesis starts with a group of general S-parameters that consider both amplitude and phase responses as well as complex terminations for an Nth-order filter. A transversal array network incorporating resonators as well as non-resonating nodes is then introduced to accommodate the given S-parameters. In result, a canonical (N + 2) × (N + 2) coupling matrix with newly defined source–source and load–load couplings is generated. Some examples, including a fully canonical prototype and a mixed topology diplexer, are demonstrated to show the flexibility of the methodology. Moreover, an eighth-order coaxial cavity filter, with a −120° additional phase shift for S-parameters, is designed and fabricated. The measured results are well consistent with the synthesis ones, which validates the availability of this study in physical implementations.

Coaxial cavity waveguide antennas excited by stacked circular microstrip patches for use as prime-focus reflector feeds

A coaxial cavity antenna excited by a stacked circular microstrip antenna is investigated as a feed for prime-focus parabolic reflector antennas. The radiation pattern of the proposed cavity-backed antenna is saddle shaped, which widens the −10 dB beamwidths and increases the reflector efficiency especially for deep reflectors with small focal length-to-diameter ratios. With a single-probe feed, the co-polar radiation pattern is slightly asymmetric in the E-plane, but is made symmetric by a differential feeding technique, using two probes. The impedance bandwidth of the proposed feed antenna is 20%. The antenna was fabricated and tested, and it exhibited good agreement between simulation and measurement results. The gain factor of the feed was also studied with a circular-symmetric reflector and provided a gain factor of 79% at f/D = 0.375. This type of feed can be used as an alternative to conventional horn or waveguide feeds, where reduced size and light-weight are desirable with added advantage of easy integration with electronics.

A Technique to Suppress Harmonic Outputs in Coaxial Cavity Filters at the Excitation Port

A technique to improve the spurious performance of coaxial cavity filters is investigated. It involves incorporating elements/posts resonant at spurious frequencies within the coaxial input/output cavites. To perform suppression and control of harmonic outputs, the spurious elements are coupled directly to the excitation posts and prevent the excitation of harmonics at the fundamental elements. The spurious elements are physically significantly smaller than the fundamental elements that perform the basic filtering function (fundamental frequency); thus they impose only minimized degradation to the ohmic loss of the devices and miniscule additional design effort. Design guidelines of the proposed filters are given. Obtained results demonstrate significant improvement in the spurious performance, and experimental results verify the concept.

A NOVEL MICROWAVE SENSOR WITH HIGH-Q SYMMETRICAL SPLIT RING RESONATOR FOR MATERIAL PROPERTIES MEASUREMENT

A new sensor based on symmetrical split ring resonator (SSRR) functioning at microwave frequencies has been proposed in order to detect and characterize the properties of the materials. This sensor is based on perturbation theory, in which the dielectric properties of the material affect the quality factor and resonance frequency of the microwave resonator. Conventionally, coaxial cavity, waveguide, dielectric resonator techniques have been used for characterizing materials. However, these techniques are often large, and expensive to build, which restricts their use in many important applications. Thus, the proposed bio-sensing technique presents advantages such as high measurement sensitivity (around 400 Q-factor) with the capability of suppressing undesired harmonic spurious and permits potentially material characterization and determination. Hence, using a specific experimental methodology, tests performed have demonstrated the biosensor ability to characterize at least four references materials with known permittivity (Air, Roger Duriod RT 5880, Roger Duriod RT 4530, FR4) and one material with unknown permittivity (Beef). Accordingly, the numerically established relations are experimentally verified for these reference materials and the results indicated that the average estimation error of measuring the permittivity was 2.56 % at resonant of around 2.2 GHz. The proposed design is useful for various applications such as food industry, medicine, pharmacy, bio-sensing and quality control

Analysis of Plasma-Loaded Noncorrugated and Triangular Corrugated Coaxial Cavity

A field analysis of plasma-loaded noncorrugated coaxial cavity and plasma-loaded triangular corrugated cavities for megawatt-class gyrotrons has been undertaken. The presence of magnetic field in plasma changes its characteristics to an anisotropic media. In plasma waveguide, three families of modes can exist: plasma modes (space charge modes), cyclotron modes, and waveguide EH and HE modes. The modes present in the plasma are hybrid modes with all six nonzero field components. The presence of the low-density plasma in a gyrotron cavity leads to the coupling of these families of modes and causes a shift in the eigenvalue of the operating (desired) mode. In this paper, the dispersion relation for a plasma-loaded noncorrugated and triangular corrugated coaxial cavity has been derived. For the gyrotron case, where the cyclotron frequency of the plasma is approximately equal to the operating frequency and the operating frequency is near mode cutoff frequency in the cavity, the desired HE mode couples with the cyclotron mode. This coupling leads to shift in the eigenvalue of the HE mode.

Direct Voltage Depression Calculation of Arbitrary Electron Beams in Misaligned Coaxial Gyrotron Cavities

Coaxial-cavity gyrotrons for electron cyclotron heating in plasma experiments for nuclear fusion can operate with very high-order modes, having reduced mode competition and decreased voltage depression compared with hollow-cavity tubes. However, since exact alignment of coaxial insert and cavity wall can only be ensured up to a certain precision, the effects of misalignment must be properly understood. In this paper, an efficient method is presented to determine the voltage depression on beam electrons for arbitrary misalignment between cavity wall and insert, and for a beam with arbitrary shape and density distribution. The method has been verified using a 3-D code, and it can be generalized to some other geometries.

Different optical properties in different periodic slot cavity geometrical morphologies**Project supported by the National Natural Science Foundation of China (Grant No. 61178044), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20160969), and the University Postgraduate Research and Innovation Project of Jiangsu Province, China (Grant No. KYLX_0723).

In this paper, optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain (FDTD) simulation method. By simulating reflectance spectra, electric field distribution, and charge distribution, we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light, in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity. A coaxial waveguide mode TE11 will exist in these annular cavities, and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities. These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss. The formation of an absorption peak can be explained from the aspect of phase matching conditions. We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps, gap surface topography. Meanwhile, different lengths of the cavity may cause the shift of resonance dips. Also, we study the field enhancement at different vertical locations of the slit. In addition, dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths, which make the annular cavities good candidates for refractive index sensors. The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity. Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates, refractive index sensors, nano-lasers, and optical trappers.

Isothermal Permeability of the Argillaceous Cobourg Limestone

The paper presents the results of an experimental evaluation of the permeability of the heterogeneous argillaceous limestone from the Cobourg formation located in southern Ontario, Canada. The low permeability of the limestone necessitated the development of experimental techniques for effectively measuring the permeability of the rock. In particular, we examine the results of pressurization of a fluid-filled co-axial cylindrical cavity of finite length cored into a 150 mm diameter cylinder of the Cobourg Limestone. The orientation of the cavity is either normal to or along the nominal stratifications identified by the argillaceous partings separating the quartzitic phases. Both steady state and transient tests are used to estimate the permeability of the Cobourg Limestone. The paper also investigates the influence of a nominal axial load on the permeability of the rock.

Overhauser Geomagnetic Sensor Based on the Dynamic Nuclear Polarization Effect for Magnetic Prospecting.

Based on the dynamic nuclear polarization (DNP) effect, an alternative design of an Overhauser geomagnetic sensor is presented that enhances the proton polarization and increases the amplitude of the free induction decay (FID) signal. The short-pulse method is adopted to rotate the enhanced proton magnetization into the plane of precession to create an FID signal. To reduce the negative effect of the powerful electromagnetic interference, the design of the anti-interference of the pick-up coil is studied. Furthermore, the radio frequency polarization method based on the capacitive-loaded coaxial cavity is proposed to improve the quality factor of the resonant circuit. In addition, a special test instrument is designed that enables the simultaneous testing of the classical proton precession and the Overhauser sensor. Overall, comparison experiments with and without the free radical of the Overhauser sensors show that the DNP effect does effectively improve the amplitude and quality of the FID signal, and the magnetic sensitivity, resolution and range reach to 10 pT/Hz@1 Hz, 0.0023 nT and 20–100 T, respectively.

Compact Dual-Mode Substrate Integrated Waveguide Coaxial Cavity for Bandpass Filter Design

This letter proposes a new compact filtering building block. It consists of two via holes embedded into a substrate integrated waveguide (SIW) cavity connected to capacitive metal patches at the top layer. This topology provides two coaxial modes performing a doublet filtering configuration. The proposed dual-mode SIW coaxial cavity is studied in detail and guidelines for the filter design are given. As will be shown, the proposed building block presents a high degree of design flexibility, which allows for the design of multiple kind of bandpass filter (BPF) responses, including both narrow- and wide-band BPFs along with transmission zero generation. As a verification, several filters are designed and implemented at 8 GHz.

Design study of double-layer beam trajectory accelerator based on the Rhodotron structure

In this paper, the conceptual design of a new structure of industrial electron accelerator based on the Rhodotron accelerator is presented and its properties are compared with those of Rhodotron-TT200 accelerator. The main goal of this study was to reduce the power of RF system of accelerator at the same output electron beam energy. The main difference between the new accelerator structure with the Rhodotron accelerator is the length of the coaxial cavity that is equal to the wavelength at the resonant frequency. Also two sets of bending magnets were used around the acceleration cavity in two layers. In the new structure, the beam crosses several times in the coaxial cavity by the bending magnets around the cavity at the first layer and then is transferred to the second layer using the central bending magnet. The acceleration process in the second layer is similar to the first layer. Hence, the energy of the electron beam will be doubled. The electrical power consumption of the RF system and magnet system were calculated and simulated for the new accelerator structure and TT200. Comparing the calculated and simulated results of the TT200 with those of experimental results revealed good agreement. The results showed that the overall electrical power consumption of the new accelerator structure was less than that of the TT200 at the same energy and power of the electron beam. As such, the electrical efficiency of the new structure was improved.

Selectivity Properties of Coaxial Gyrotron Cavities With Mode Converting Corrugations

Longitudinally corrugated inserts have been proposed as an additional mean to enhance the selectivity properties of coaxial gyrotron cavities. However, when increasing the frequency and the output power, the corrugated insert may not be sufficient to ensure mode stability. Vane loaded cavities with corrugated inserts seem to have the potential for superior mode selectivity and could be employed to facilitate the development of multimegawatt gyrotrons. In this paper, a numerical code based on the spatial harmonics method is used to study the spectrum rearrangement of a typical coaxial cavity with corrugated insert in which additional wedge-shaped corrugations are introduced on the outer wall. A general design procedure for the upgrade of the mode selectivity is presented. Its merits are demonstrated for a 140-GHz gyrotron cavity.