Coaxial Cavity Resonator Research Articles

Microwave Coaxial Line Cavity Resonator Sensor for Thickness Measurement of Coatings on Fiber-Reinforced Polymer Composites

Microwave Coaxial Line Cavity Resonator Sensor for Thickness Measurement of Coatings on Fiber-Reinforced Polymer Composites

An X-band coaxial relativistic klystron oscillator with a novel diode structure packaged with permanent magnet

To achieve compactness and miniaturization for high-power microwave devices, this paper proposes an X-band permanent magnet-packaged coaxial relativistic klystron oscillator (RKO) with a novel diode structure featuring a stair-step cathode. First, by adopting a large-radius anode structure, the emission of beam currents from the side of the cathode surface is diminished, thereby reducing the proportion of the backward current in the beam current from 10% to 7%. Second, a stair-step cathode is used to inhibit the return flow of electron beams from striking the anode and generating plasma. Concurrently, a radially non-uniform coaxial resonant cavity structure is employed to enhance the fundamental wave modulation depth of the electron beam and improve the beam–wave interaction's efficiency. The experimental results show that the novel device outputs a microwave with a frequency of 9.46 GHz and a pulse width of 55 ns. It generates a power output of 1.5 GW with an efficiency of approximately 30.5%, in the case in which the diode voltage is 505 kV, the beam current is 9.7 kA, and the guiding magnetic flux density is 0.4 T. This novel structure surpasses traditional diode configurations by enhancing the beam-to-wave conversion efficiency by roughly 10%, thereby offering substantial support for the compactness and miniaturization of RKO.

A low-frequency normal conducting cavity with higher-order mode damping for fourth-generation synchrotron radiation sources.

The utilization of a low-frequency (<200MHz) RF system in storage facilitates the attainment of ultra-low emittances in synchrotron light sources through on-axis injection. This paper focuses on the development of a low-frequency normal conducting (NC) cavity with higher-order mode (HOM) damping for fourth-generation synchrotron light sources. We propose a novel approach to achieve efficient HOM damping in a NC cavity by optimizing the lowest frequency HOM and implementing a beam-line absorber. Notably, unlike conventional NC cavities, the presence of a large beam tube for the beam-line absorber does not compromise the accelerating performance in a coaxial resonant cavity, enabling effective HOM damping while maintaining a high shunt impedance. Through simulations, the prototype design of a 166.6MHz HOM-damped cavity demonstrates a fundamental mode impedance of ∼8 MΩ, with longitudinal and transverse HOM impedances below 2.0 and 50 kΩ/m, respectively.

Three Dimensional Printed Vertically-Stacked Single-/Multi-Band Coaxial Filters and RF Diplexers

This article reports on monolithically integrated and low form-factor vertically-stacked coaxial resonator-based single-/multi-band filters and radio frequency (RF) diplexers using stereolithography apparatus (SLA) additive manufacturing (AM). The proposed RF filtering/diplexer concepts exhibit the following unique features: 1) low form-factor due to the use of vertically stacked low-profile capacitively-loaded coaxial cavity resonators; 2) monolithic integration; and 3) versatile and highly selective transfer functions facilitated by the topological arrangements of the resonators within the filter volume that enable cross-couplings and can be exploited to increase selectivity. Theoretical filter design analysis using coupling routing diagrams (CRDs) and eigen-mode electromagnetic (EM) simulations are performed. The proposed concept is validated by the design, fabrication, and testing of four monolithically-integrated prototypes, namely a four-pole two transmission zeros (TZs) bandpass filter (BPF), a three-pole two TZs BPF, a second-order dual-band BPF, and a second-order diplexer operating at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> -band and exhibiting an effective quality factors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{eff}}s)$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 700.

Beam dynamics optimization design of Rhodotron electron accelerator based on genetic algorithm and sensitivity analysis

The beam dynamics optimization study of Rhodotron electron accelerator for irradiation sterilization is introduced in this paper. The Rhodotron accelerator acceleration principle and the RF field distribution in the coaxial resonant cavity are described in detail. Beam dynamics in the Rhodotron accelerator are analyzed from both transverse and longitudinal directions. Beam dynamics of two kinds of Rhodotron electron accelerators with maximum beam energy of 10 MeV and 40 MeV were optimized based on multi-objective genetic algorithm. The key parameters of Rhodotron accelerators are determined, and the influence of some parameters on the overall acceleration effect is quantitatively analyzed. This paper provides some references for the research, manufacture, installation, and commissioning of this type of accelerator.

Monolithically Integrated Coaxial Resonator-Based Filtennas Using SLA Three-Dimensional Printing

This letter reports on a new class of highly-miniaturized coaxial-resonator-based filtennas alongside a monolithic integration concept using digital additive manufacturing. The filtenna approach is based on the co-design of a coaxial cavity resonator and an annular slot antenna that collectively perform as a radiating resonating node within a coupled-resonator-based bandpass filter. Beam direction can be controlled by altering the position of the radiating slot. A stereolithography apparatus (SLA) monolithic integration concept is proposed for size compactness and reduced weight. For proof-of-concept validation purposes, first-, second-, and third-order filtennas were analyzed through electromagnetic simulations. Experimental validation was performed through the manufacturing and testing of a second-order top-slot filtenna, a second-order and a third-order side-slot filtenna with the following characteristics: center frequency: 4.75 GHz, 4.8 GHz and 4.6 GHz, fractional bandwidth: 7.4%, 8.3%, and 7.6% and realized gain: 5.5 dBi, 2.6 dBi, and 2.6 dBi.

Coaxial resonant cavity for measuring complex permittivity of liquids

Abstract In this letter, a new microwave sensor of the coaxial resonant cavity with a single-open-ended circuit loaded capacitor is proposed and used to detect the liquids’ complex permittivity. The improved cavity has a higher internal electric field and smaller size when compared with the cylindrical cavity, which gives the sensor a high sensitivity in measuring liquids’ complex permittivity. A coaxial resonant cavity operating in 1.9 GHz was designed in this work. The silicone hose used for the test is inserted vertically from the center of the cavity, and the liquids under test (LUTs) are guaranteed to be 2 ml each time. The dielectric properties of LUTs will cause perturbation to the internal electric field of the cavity. By analyzing the measured data, the sensitivity of the cavity is 0.12%, and the relative errors of the real part of the measured value and the reference value are 3.67%. which shows the measured value has a good agreement with the reference value.

A Resonant Cavity Based on Capacitively Loaded Coaxial Structure for Overhauser Magnetic Sensors

The RF excitation coil is an important component of the Overhauser magnetic sensor, which determines whether the dynamic nucleation polarization of the free radical solution can be carried out smoothly. A capacitance-loaded resonant cavity structure is proposed as the RF excitation of the Overhauser magnetic sensor. The structure and equivalent circuit of the capacitance-loaded coaxial resonant cavity are analyzed and improved on the conventional structure, and the resonant frequency is verified to be consistent with the excitation frequency of the free radical solution by modeling and simulation using COMSOL software. The resonant cavity solid was fabricated, and the cavity was tested by using a vector network analyzer. The results show that the initial resonance point of the homemade resonant cavity is 60.55MHz, and the frequency point can be adjusted to 60.7MHz by adjusting the loading capacitor and tuning capacitor; the resonant cavity return loss S11 is about -19dB, and the quality factor Q value is about 506.

Design of a small size C‐band cavity bandpass filter

AbstractThis letter proposed a new topology of a cavity bandpass filter, with which a C‐band small size bandpass cavity filter is realized. The filter adopts a capacitor‐loaded open terminal coaxial resonant cavity, the Q factor of which is greater than 7000, with the 50 Ohm coaxial lines as the input and output ports. By building an equivalent circuit, the coupling matrix is synthesized to obtain the characteristics between the resonators. The cascaded quadruplet section with inductive cross‐coupling and the folded structure is adopted to make the volume smaller and more compact than the traditional filter. The measured results show that the standing wave ratio of the filter in the whole 500 MHz passband is less than 1.22, and the rejection at 3500 MHz and 4500 MHz reaches −70 dB.

A Tunable Filtering Antenna Based on Coaxial Cavity Resonators

In this article, a method for designing a tunable coaxial filtering antenna is presented. The proposed filtering antenna has a simple structure, consisting of a standard waveguide and some metal cylinders. Instead of utilizing traditional coupling irises, an all-cylinder coupling structure is employed for flexible tuning. Thus, the center frequency and bandwidth of the coaxial filtering antenna can be conveniently tuned by adjusting the lengths of the cylinders. Theoretical analysis and design process of the filtering antenna are given in detail. A third-order tunable filtering antenna with Chebyshev response is designed to verify this method. The tunable range of the center frequency is from 9.25 to 10.75 GHz, and the tunable range of the fractional bandwidth (FBW) is from 2% to 8%. The measured gain of the antenna is flat and greater than 6.5 dBi along the tuning range. In addition, the antenna maintains good impedance and radiation characteristics throughout the tuning range.

Numerical and experimental studys of coaxial cavity resonator with a measuring gap

Numerical and experimental studys of coaxial cavity resonator with a measuring gap

Compact Quadruple-Mode Wideband Bandpass Filter Using L-Shaped Feed-Line in a Single Cavity

This letter presents a novel quadruple-mode cavity wideband bandpass filter (BPF). Unlike the conventional coaxial cavity resonator, the proposed cavity resonator is made up of two symmetrical conductive posts in a cylindrical cavity, while four resonant modes of the cavity resonator are classified as TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode, and a pair of TE degenerate modes (TE+ mode and TE− mode). All of the four modes are excited by a pair of L-shaped feed-lines. In addition, the four resonant modes are employed to constitute the passband of wideband BPF with a fractional bandwidth (FBW) of 45% at the central frequency of 2.2 GHz. Finally, the proposed filter is designed and fabricated. Good in-band filtering performance, wide upper stopband, and compact size are realized.

A Miniaturized Single-Wall Carbon Nanotubes Field Emission Cathode With RF Excited by Coaxial Resonant Cavity

A miniaturized radio frequency (RF) excited grid-free field emission cathode made by single-wall carbon nanotubes (SWCNTs) is suggested and studied. The λ/4 coaxial resonant cavity is used as field-emitted electron source with length of 26.5 mm and diameter of 12.8 mm. Electrons can be pulled out by a small electrostatic field and an RF electric field without interception. The RF electric field of inner conductor surface at the open end, which pasted SWCNTs, can reach 3 MV/m when the input power is 30 W, and the field is larger than the turn-on field of SWCNTs. The results of simulation and experiment both show that the maximum emission current under input RF power of 30 W is 30 times larger than without RF excitation, which can reach 24 mA at the anode voltage of 950 V. This miniaturized RF excited grid-free field emission cathode electron source can be used as electron source, in a high repetition frequency vacuum electronic devices, e.g., terahertz (THz) devices, and X-ray tubes.

Multi-conductor coaxial cavity resonators for miniaturization of UHF bandpass filters

In this paper, we present the compact bandpass cavity filters for UHF range. We investigate the properties of coaxial resonators with various numbers of tubular posts from one to four. We show that the resonant frequency can be four times smaller for the four-post resonator in comparison with the single post resonator with the same cavity dimensions. We synthesized and manufactured fifth-order bandpass cavity filter on four-post coaxial resonators for the 690–806 MHz frequency range with 20-dB return loss. The filter dimensions were 30 mm × 44 mm × 127 mm. We also synthesized and manufactured the fifth-order bandpass cavity filter on four-post coaxial resonators with inductive and capacitive cross-coupling between first and fifth resonators to provide transmission zeros in amplitude–frequency characteristic in lower- and upper-frequency band, respectively. Comparison with the standard double-post coaxial cavity filters demonstrates more than 30% volume reduction with similar transmission characteristics.

Imaging nano-defects of metal waveguides using the microwave cavity interference enhancement method

Here, we demonstrate a microwave (MW) cavity interference enhancement method to image nano-defects on the surface of metal waveguide. The MW cavity interference system mainly consisted of a MW coaxial resonant cavity with a nano-probe. The MW signals have been evenly divided into two channels. One was the reference signal inputted into the MW waveguide and coupled into the MW cavity via the probe. Also, the coupling strength depends on the distance between the probe and the MW waveguide. Another one was directly inputted the MW cavity to interfere with the reference signal, and was enhanced in the cavity. Then, the surface topography of the metal waveguide was mapped by calculating the enhanced signals. In our experiment, a weak signal of ∼1 pW coupled from the waveguide can be detected by a MW cavity with the quality factor of ∼209. As a proof of application, the topography of nano-defects on the surface of metal waveguide in an MW chip has been mapped with a resolution of ∼15 nm. We have proved that this is a high-resolution, easy-to-manufacture, low-cost, and real-time online monitoring approach for online assessment and screening chips. This potentially has broad applications in the fields of chip manufacturing, chip inspection, nano-structure detection, and so on.

Microwave characteristics analysis of photosensitive material InP under weak optical irradiation

In this paper, the microwave characteristic of photosensitive material InP irradiated by different optical signals is studied based on the coaxial resonant cavity. The coaxial resonant cavity sensor has an operating frequency range from 1 to 4 GHz, an operating mode of TEMn/4, and a quality factor of 8000 or more. According to the theory of semiconductor and electromagnetic field, the equation describing the relationship between the irradiation power and the quality factor of the coaxial resonator is derived. Additionally, in the short-time irradiation experiment, the variation of microwave characteristics of InP with irradiation power of 10mW, 50mW, 100mW, and 250mW is studied by frequency-domain and time-domain scanning methods, respectively. The measurement results indicate that the microwave characteristic variation of the InP under short-time weak power irradiation is mainly caused by the non-thermal effect, while the thermal effect is not obvious. In order to investigate the influence of thermal effect on the microwave characteristic of InP under continuous illumination, taking the irradiation power of 100mW as an example, the irradiation experiment with a duration of 1 min is performed on the InP. The thermal and non-thermal effects at the moment of opening and closing of the monochrome light source and during irradiation are analyzed. Furthermore, the stability and response speed of the system are analyzed and tested, and the measurement results are in good agreement with the theoretical analysis.

Tunable Coaxial Cavity Resonator-Based Filters Using Actuated Liquid Metal Posts

This letter presents a new tuning method for coaxial cavity resonator-based bandpass filters (BPFs). The proposed tuning mechanism lays its foundations on pneumatically-actuated Galinstan that functionalizes the inner conductor of a capacitively-loaded coaxial cavity resonator. By altering the volume of Galinstan (i.e., height of inner conductor), ultrawide (>octave) and low loss RF tuning can be obtained without the need for small capacitive gaps that typically limit the RF performance of coaxial BPFs. To validate the concept, a coaxial cavity resonator with frequency tuning between 2.9 and 9.9 GHz (3.4:1 tuning range), and unloaded quality factor between 120 and 625 was manufactured and measured. Furthermore, the RF performance of a two-pole BPF with: 1) tunable frequency between 3.4 and 7.5 GHz (2.2:1); 2) an intrinsically switched-off state; 3) insertion loss <1 dB; and 4) return loss <10.5 dB was experimentally validated.

Compact $S$ -Band Coaxial Cavity Resonator Filter Fabricated By 3-D Printing

This letter presents a novel fourth-order coaxial cavity resonator bandpass filter with a Chebyshev response. The filter operates at a center frequency of 3 GHz and has a bandwidth of 90 MHz. The filter is formed of four coupled coaxial cavity resonators. To make the filter compact, the first resonator is embedded inside the inner conductor of the second resonator and the fourth resonator is embedded inside the central conductor of the third resonator. The filter is fabricated stereolithography apparatus 3-D by printing process that allows such a design with a complex structure to be fabricated accurately at a reasonable cost. The filter is tested and good agreement between measured and simulated results is obtained.

Near-field scanning microwave microscope platform based on a coaxial cavity resonator for the characterization of semiconductor structures

A Near-Field Scanning Microwave Microscope (NSMM) for the characterization of semiconductor structures has been designed, simulated and fabricated. The present NSMM system is based on a home-made coaxial-cavity resonator which is fed by a Keysight N5242A PNA-X Network Analyzer. The inner conductor of the coaxial resonator is connected to a sharpened tungsten tip, which was fabricated by an electrochemical process. The reflection and transmission coefficients S11, S21, the resonance frequency fr and the quality factor Q of the resonant cavity are measured as the semiconductor structure is scanned by the sharpened probe tip while the sample-tip distance is kept constant in the near-field region. The interaction between the probe tip and the sample under test provides variations of these parameters which are related to the topographical and dielectric properties of a very small region of the material under the probe tip. Thus, a 2D image of the evolution of the S11, S21, fr and Q parameters on the surface of the device under test is obtained. This image can be related to space changes in the topography, dielectric properties and composition of the semiconductor structure.

A Circularly Polarized Single-Frequency Multimode Helical Beam Antenna

An antenna based on a TM coaxial resonant cavity with radiating annular slots on one face and excited by multiple open-ended TE mode coaxial resonators on the opposite face is shown to simultaneously radiate the corresponding circularly polarized helical beams modes over a single-frequency band with good isolation between modes. S-parameters are calculated for a transmit–receive configuration with the antennas separated by 10 wavelengths. The initial antenna concept was developed interactively using the conformal finite difference time domain method with a Titan-XP GPU.