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The tuning of microwave cavity filters (MCFs) is a complex process to improve the filtering performance. In practice, the tuning is mostly conducted in a manual way, and thus is time and resource intensive. Toward the demand for automatic tuning of MCFs with high accuracy and efficiency, this article proposes an intelligent tuning method for MCFs via modeling and optimization. The main contributions are threefold as follows: 1) A series of performance evaluation functions are defined to comprehensively characterize the tuning output; 2) a block modeling method is proposed to construct the electromechanical characteristic model to facilitate the calculation of the cost function; 3) an improved particle swarm optimization (PSO) algorithm, named granular multi-swarm PSO (GMS-PSO), is proposed to achieve quick search of optimal combinations of the tunable components. The effectiveness and practicality of the proposed method are demonstrated by experiments with a real intelligent tuning system.

We describe the observation of a previously unreported resonance phenomenon in UWB SAR imaging and its application in a novel scheme for the retrieval of thickness and dielectric properties of scene features. The resonance was observed in a 14–50 GHz laboratory study of very high resolution SAR imagery. It presented as a periodic fluctuation in the backscatter of a scene feature in response to changes in the radar measurement frequency. The complimentary static reflectivity measurements of a range of dielectric materials showed the phenomenon could be understood as a material behaving as a resonant microwave cavity. Modeling simulations were able to accurately reproduce the observed nulling characteristics for visually homogeneous materials (acrylic, MDF, and plasterboard) and which displayed a regular frequency spacing between nulls. Those with inhomogeneous structures (chipboard and plywood) showed much more irregular nulling patterns. The spacing of the backscatter nulls is set by the product of the permittivity and thickness of the material. By exploiting diversity in viewing geometry, the two terms can be separated and measured. The scheme offers a new opportunity in the SAR surveillance and monitoring of man-made structures.

In this study, the main focus is laid on the design of an optoelectronic converter as a part of the quantum radar to enhance the entanglement between retained and returned modes at high temperatures. The electro-opto-mechanical converter has been widely studied, and the results showed that the operation at high temperature is so crucial to generate and preserve the entanglement between modes. The main problem arises because the mechanical part operating at a low frequency leads to a large number of thermally excited photons, and eventually, the entanglement between modes becomes lost. To solve the problem, we replace the mechanical part with the optoelectronic components. The optical cavity is coupled to the microwave cavity in the newly designed system through a Varactor diode excited by a photodetector. As the main goal, to improve the entanglement sustainability, the effect of the coupling factor of the microwave cavity to photodetector is investigated. The results show that the mentioned factor creates some degrees of freedom to enhance the entanglement at high temperatures compared to the electro-opto-mechanical converter. At some specific values of the coupling factor, the retained and returned fields remained completely entangled up to 5.5 K and partially entangled around 50 K.

The electron density of the nonstationary atmospheric pressure discharge in a helium flow is estimated using microwave cavity resonance spectroscopy. For this, a measurement scheme was developed based on a spectrum analyzer and a cylindrical resonator with the first three transverse electric (TE) eigenmodes in the range of 1–1.5 GHz. The main working mode was the TE TE112 mode, which made it possible to place the high-frequency measuring and discharge power supply circuits in the most optimal geometry. By measuring the eigenfrequency shift of this mode and its $Q$ factor, gas-discharge plasma parameters were calculated using the well-known perturbation theory. The results are in good agreement with the known data from the literature. This method was additionally tested on a glass rod and a thin low-pressure gas discharge tube.

We present an experimental characterisation of the electrical properties of 3D-printed Niobium. The study was performed by inserting a 3D-printed Nb post inside an Aluminium cylindrical cavity, forming a 3D lumped element re-entrant microwave cavity resonator. The resonator was cooled to temperatures below the critical temperature of Niobium (9.25K) and then Aluminium (1.2K), while measuring the quality factors of the electromagnetic resonances. This was then compared with finite element analysis of the cavity and a measurement of the same cavity with an Aluminium post of similar dimensions and frequency, to extract the surface resistance of the Niobium post. The 3D-printed Niobium exhibited a transition to the superconducting state at a similar temperature to the regular Niobium, as well as a surface resistance of $3.1\times10^{-4}$ $\Omega$. This value was comparable to many samples of traditionally machined Niobium previously studied without specialised surface treatment. Furthermore, this study demonstrates a simple new method for characterizing the material properties of a relatively small and geometrically simple sample of superconductor, which could be easily applied to other materials, particularly 3D-printed materials. Further research and development in additive manufacturing may see the application of 3D-printed Niobium in not only superconducting cavity designs, but in the innovative technology of the future., Comment: 5 pages, 4 figures

In this article, an attractive resonant technique is devised for calculating the dielectric properties of arbitrary length material under test (ALMUT), which is partially filled inside a waveguide cavity sensor. The proposed technique exempts two major assumptions viz. the depolarization effect and the theory of images, which were neglected in earlier cavity perturbation methods. A numerical model of the depolarizing factor, which precisely considers the impact of the relative permittivity and the sinusoidal variation of the electric field, is also formulated. First, the technical modification and the numerical analysis are provided and after that, a new set of formulas for characterizing the complex permittivity of ALMUT is developed. The numerical results suggest the accuracy and validity of the scheme for a broad range of dielectric samples, including the typical case, i.e., the full-length dielectric sample. The novelty of the presented technique can be ascertained from the fact that it provides higher accuracy irrespective of the actual sample length when compared with standard cavity techniques. A few standard dielectric samples with the partially filled arrangement are measured using the WR90 cavity, and the results are compared with their corresponding values obtained using the earlier reported conventional and modified techniques. It is found that the results evaluated using the devised scheme are consistent and independent of the actual dimensions of ALMUT. On the other hand, error in estimated complex permittivity using the earlier reported approaches shows substantial dependence on the sample size.

[EN] This paper reports the development of a stand-alone and portable instrument designed to measure the complex permittivity of dielectric materials at microwave frequencies. The equipment consists of an in-house single-port vectorial reflectometer and a resonant coaxial bi-reentrant microwave cavity where the material under test is placed inside a Pyrex vial, making the device appropriate for measuring liquids, semi-solids, powders and granular materials. The relation between the dielectric properties of the involved materials and the cavity resonance has been solved by numerical methods based on mode-matching and circuit analysis. In order to increase the measurement range, so that low to high loss materials can be characterized in the same cavity, the effect of the coupling network is de-embedded from the resonance measurements. The performance of the newly devised instrument is evaluated by error/uncertainty analysis and comparative studies with other well-established instruments and methods. Errors lower than 2% in the dielectric constant, and 5% in the loss factor, are found. This simple, portable, affordable and robust device could help non-specialized personnel to accurately measure dielectric properties of materials used in a wide range of microwave applications., This paper has been financially supported through the grant reference BES-2016-077296 of the call Convocatoria de las ayudas para contratos predoctorales para la formacion de doctores de 2016 by Ministerio de Economia y Competitividad (MINECO) and by European Social Funds (ESF) of European Union and the project SEDMICRON TEC2015-70272-R (MINECO/FEDER) supported by Ministerio de Economia y Competitividad (MINECO) and by European Regional Development Funds (ERDF) of European Union. The Associate Editor coordinating the review process was Samir Trabelsi.

Dielectric measurements offer the possibility of highly sensitive detection of physical cell properties, and are of interest for clinical applications due to their non-destructive nature and the lack of need for cell labelling. Here we report sensitive measurements on single, living, free-flowing cells (not electrostatically or dielectrophoretically trapped, cultured or fixed directly on sensing elements) in aqueous medium at ∼9.8 GHz taken using a coupled dielectric-split ring resonator assembly. Inductive coupling between the two resonators enabled separation of microfluidic chips from RF connectors and allowed for time-resolved continuous-wave measurements on flowing single cells via the coaxial ports of a dielectric-loaded microwave cavity. Analysis via an equivalent circuit model showed that the novel resonator assembly maintained the permittivity-dependent sensitivity of a split ring resonator while operating at quality factors >1000 with lossy aqueous media (typically ∼1900). Using a microfluidic channel with a 300 × 300 μm cross section, at a water-loaded resonant amplitude of ∼−22 dB at 0 dBm input power level, shifts in amplitude due to individual cells passing through the sensing region of up to −0.0015 dB were observed. Correlations between averaged amplitude shifts and cell size as well as material properties demonstrate the diagnostic potential of this technique.

In this study, plasmonic opto-mechanical tripartite system is proposed to improve the performance of the traditional tripartite opto-mechanical system. In the new design, significantly, optical cavity and microwave cavity modes are directly coupled to each other. The originality of this work consists in embedding a microsphere in the optical cavity where the plasmon-plasmon interaction between the metal plates generates a plasmon mode inside the optical cavity and changes the electric field distribution. The plasmonic property influences the microsphere electrical properties and interacts with the photonic mode inside the optical cavity by which the microwave cavity properties are also affected through coupling to the optical cavity. Microsphere introduces a capacitor as a function of plasmonic properties that can strongly influence the microwave cavity resonance frequency. That is the feature that we want to utilize to enhance the performance of the system at high temperature. The results show that the optical cavity and microwave cavity modes remain entangled at high temperature. It is contributed to the plasmonic-based capacitor induced by the microsphere which is not affected by the thermally induced photons (noise). It is worth mentioning that the induced noise strongly restricts the traditional tripartite system operated with a wide bandwidth.

We report a high-performance pulsed optically pumped (POP) Rb clock based on a novel magnetron-type microwave cavity. The cavity has a volume of 30 mL, enabling a highly homogenous microwave field distribution. With the laser frequency tuning to the ground-state hyperfine level ${F}= {2}$ of the ${D}_{{2}}$ line, we observe a Ramsey fringe contrast of 52% in terms of optical absorption detection. The resultant shot noise limit is estimated to be ${1.6} \,\times \, {10}^{-{14}}{\tau }^{-\text {1/2}}$ . The clock frequency stability is measured as ${2.3}\,\times \, {10}^{-{13}}\tau ^{-\text {1/2}}$ (1–100 s), which is limited by the relative intensity noise of the light.

In this article, Au/As2Se3/Ag/As2Se3/Yb Schottky barriers are formed and characterized. The devices prepared by the thermal evaporation technique under vacuum pressure of 10−5 mbar are observed to exhibit metal-induced crystallization process when coated onto Au substrates. Electrically, the arsenic selenide-based Schottky devices exhibited typical metal-oxide-semiconductor (MOS) characteristics with a built-in potential of 0.17 eV. The device shows resonance–antiresonance switching, negative capacitance (NC) effect, and high to low conductance switching features in the frequency domain of 10–1800 MHz. In addition, measurement of the impedance, amplitude of reflection coefficient, return loss ( ${L}_{r}$ ), and voltage standing wave ratio (VSWR) spectra in the same domain have shown that the Au/As2Se3/Ag/As2Se3/Yb Schottky barriers display band stop features at 1180 MHz. The ${L}_{r}$ and VSWR values at this critical frequency are 29.1 dB and 1.1, respectively. The electrical characterizations of the Au/As2Se3/Ag/As2Se3/Yb MOS devices have confirmed their suitability for use as parasitic capacitance cancellers, noise reducers, and as switching clock with selective switching time scales of switching delay time less than 0.40 ns.

As superconducting quantum processors increase in size and complexity, the scalability of standard techniques for qubit control and readout becomes a limiting factor. Replacing room temperature analog components with cryogenic digital components could allow for the realization of systems well beyond the current state-of-the-art qubit arrays with tens of qubits. The standard technique for performing a qubit measurement with heterodyne readout uses a quantum-limited cryogenic amplifier chain and requires bulky microwave components inside the refrigerator with multiple control lines and pump signals. Additionally, the result is only accessible in software at room temperature. An alternative method for measuring qubits involves mapping the qubit state onto the photon occupation in a microwave cavity, followed by subsequent photon detection using a Josephson photomultiplier (JPM). The JPM measures the qubit and stores the result in a classical circulating current. To make use of this result, we can leverage existing single flux quantum (SFQ) circuitry. An underdamped Josephson transmission line (JTL) can be coupled to the JPM and fluxons traveling along the JTL are accelerated or delayed, depending on the circulating current state of the JPM. This fluxon delay can then be converted to an SFQ logic signal resulting in a digital qubit readout with a proximal microfabricated device, paving the way for cryogenic digital feedback necessary for error-correcting codes.

The cavity perturbation method is a standard technique for material parameter estimation. It typically assumes that the sample consisting of the material under test (MUT) is small. This and other assumptions are violated in in-process measurement scenarios that involve big and inhomogeneous samples. We analyze the limitations of the classical perturbation method and present a new approach toward the measurement of spatially varying material parameters associated with a large sample in a rectangular or a circular cylindrical microwave cavity. The method is based on the measurement of multiple resonance frequencies and quality factors and is validated by numerical and laboratory experiments. It is demonstrated that relative permittivities and conductivities may be measured with typical accuracies on the order of 1%.

We report on a novel semiconductor reliability technique that incorporates an electrically detected magnetic resonance (EDMR) spectrometer within a conventional semiconductor wafer probing station. EDMR is an ultrasensitive electron paramagnetic resonance technique with the capability to provide detailed physical and chemical information about reliability limiting defects in semiconductor devices. EDMR measurements have generally required a complex apparatus, not typically found in solid-state electronics laboratories. The union of a semiconductor probing station with EDMR allows powerful analytical measurements to be performed within individual devices at the wafer level. Our novel approach replaces the standard magnetic resonance microwave cavity or resonator with a small non- resonant near field microwave probe. Using this new approach we have demonstrated bipolar amplification effect and spin dependent charge pumping in various SiC based MOSFET structures. Although our studies have been limited to SiC based devices, the approach will be widely applicable to other types of MOSFETs, bipolar junction transistors, and various memory devices. The replacement of the resonance cavity with the very small non- resonant microwave probe greatly simplifies the EDMR detection scheme and allows for the incorporation of this powerful tool with a wafer probing station. We believe this scheme offers great promise for widespread utilization of EDMR in semiconductor reliability laboratories.

Microwave processing of metallic powders, both in multimode and single-mode cavity, has attracted wide interest. However, the mechanism of interaction between microwaves and metal powders is not yet very well understood. In this paper, the microwave power absorption mechanism in metallic powders has been systematically studied. For this, mixtures of copper and alumina powders have been processed in a 2.45-GHz microwave single mode cavity in either air or forming gas (N2 + 5 wt% H2). In the nominal pure magnetic field (H-field) region in the single-mode microwave cavity, pure copper powder cannot be heated in the reductive (forming gas) atmosphere while it will heat in air atmosphere. Although neither alumina nor copper separately heat up in forming gas in the H-field, mixtures of copper and alumina powders heat up readily. These behaviors can be explained by the presence of oxide layers found on many metallic particles, which play a vital role in the microwave heating of metal powders. The oxide layers isolate the particles and confine the electric current to the surface of every particle, thereby allowing microwaves to penetrate into the sample. Since the particle size is quite small and the surface area is high, the heat produced by the sum of the surface currents on all of these particles is significant. Concurrently, the oxide layer on each metal particle may act as thermal insulation material to help maintain the temperature as the metal particles heat up since many metal oxides have low thermal conductivity. We propose a new mathematical model and derive the power dissipation equation which provides the fundamental basis for the analysis, calculation, and simulation of heating of metallic powders in microwaves.

In this paper, a new family of low-profile high quality factor cavity resonators, termed distributed resonators, is introduced. Initially, the theory of operation of the proposed distributed resonator is presented regarding two, three, and four coupled resonator elements. Based on this, a further-improved arrangement of resonator elements is proposed. It is shown that the height of the individual resonator can be controlled by the number of resonant elements and can be almost arbitrarily low. As an experimental verification, a three-pole filter operating at 1800 MHz with a bandwidth of 40 MHz is designed and fabricated. The individual resonator of this filter comprises 25 individual resonant elements, with an overall cavity height of 7 mm, or 15°, and an unloaded quality factor of 1900. The height of the presented filter is significantly lower than any other air-filled filter cavity solution available in the literature. The measured insertion loss of the filter is 0.5 dB, which is in excellent agreement with the theoretically predicted value of 0.4 dB.

The paper summarizes the results of the microwave generation in atmospheric air and argon at high pressure. The method how to proceed to achieving higher power level is presented. Two experimental setups were considered. Attention is paid to the interactions between the frequencies in the resonant cavity i.e., the coherence effect. The objective is to get reproducible data and the generation of the microwave emission at the single frequency to avoid the coherence effect. The electrons in the cavity are created by the electric field and by the photoionization, enabling the population inversion to be obtained. Because of the electron impact with N2 in air, molecules cannot lose this energy by photon emission, their excited vibrational levels are metastable and live for a long time. The microwave pulse of long duration can be generated. The various radiation lines created in the resonant cavity are noted. To achieve high-power microwave emission, the resonant cavity has to be tuned to the more powerful line of the rotational and/or vibrational transition of molecules in air occurring at high frequency and not at 1-GHz frequency used in this study. A compact system could be achieved by using the high-frequency line. The study points out that the microwaves are produced through the amplification by stimulated emissions of electromagnetic radiation (maser action) in air and argon.

Application of the classical finite-element method (FEM) to the resonant cavity problem leads to nonphysical modes and expensive computational costs. In this paper, a new two-grid vector discretization scheme is presented for computing the resonant cavity problem with lossless anisotropic media in 2-D and 3-D. This scheme is based on the mixed FEM with the edge element, the shifted-inverse power method, and the Rayleigh quotient so that it cannot only successfully suppress all nonphysical modes but also significantly reduce the computational costs. In addition, this scheme is highly efficient for the microwave cavity filter and the open cavity problem. Several numerical results are provided to show that the scheme is reliable and efficient.

In this communication, we present a simple yet unconventional wideband resonant cavity antenna (RCA) with high gain and large gain-bandwidth product (GBP). The bandwidth enhancement of the RCA is approached by using a second-order height resonant cavity comprising a dielectric slab of high permittivity as the partially reflective surface and a ground plane with spherically modified geometry. It is shown that by imitating an open resonator structure, the spherically modified cavity can support multiple quasi-Laguerre–Gaussian beam modes and hence, dramatically improve the operation bandwidth of the RCA. A RCA with large GBP is designed, simulated, and then verified through measurement. Measured results show a bandwidth of 25% with a peak gain of 17.7 dBi. The proposed low-cost and easy-fabricate method shows its effectiveness in increasing the bandwidth for the RCA.

This paper describes two sets of experiments. In the first set, the ultraviolet radiation produced by the spark channel creates the photoionized plasma in air between two parallel plates. The spatial resonator formed between the two plates generates many microwave lines that are recorded by the E-field probe. Comparison is made between these results and the data obtained in the experiments done in vacuum using the electron beam. In the second set of experiments, some details of the microwave generation in atmospheric air and argon are presented. The frequency lines arising from the simple spatial resonator and from the resonant cavity are observed and recorded. The electrons are generated by the electric field and by the photoionization. Comparison between the data leads to the suggestion of the possibility to enhance the microwave power level in the plasma-assisted slow-wave oscillator.

A planar cavity is proposed, designed, and implemented with a hybrid substrate integrated waveguide (SIW) and periodically drilled SIW (PDSIW) structure. Air holes are added to synthesize a lower effective permittivity. The periodicity can increase the stored energy and improve the quality factor. The optimal ratio between the two permittivities is investigated. The measured results show that the proposed resonator has an unloaded quality factor ( ${Q}_{u}$ ) of 815, which is 53% higher than its standard SIW counterpart. To demonstrate the potential of the proposed PDSIW cavity, a third-order filter is designed and implemented through the proposed cavity, and it is then compared with filters of different orders. The new filter with a cavity shows performance enhancements in terms of both loss and bandwidth. The SIW resonator can be a promising element for use in the design of high-performance microwave filters and oscillators.

This paper presents a new class of second-order individually and continuously tunable dual- and triple-band bandpass filters in a single metal cavity. Each passband is realized by two identical metal posts. These dual- and triple-band tunable filters are achieved by putting two or three identical sets of metal-post pair in a single metal cavity. Metal screws are co-designed as a part of the metal posts to control their insertion depth inside the cavity. In this way, the resonant frequencies can be continuously controlled and designed at the desired frequency bands. Moreover, the distance between the two metal posts in a post pair can be freely tuned. Thus, the external quality factor ( $Q_{\mathrm {{e}}}$ ) and coupling coefficient ( ${k}$ ) between the adjacent modes can be easily adjusted to meet the specified requirement in synthesis design. At the bottom of the cavity, some grooves are used to extend the tunable frequency range and make the resonant frequency linearly varied with the height of the metal post. The center frequency of each passband can be independently tuned with a frequency range of 0.8–3.2 GHz and tunable ratio of 4. Finally, the continuously tunable dual- and triple-band bandpass filters prototypes with second order response are designed and fabricated, of which each passband can be individually tuned with a large tuning range.

Microwave cavity perturbation measurements are a useful way to analyze material properties. Temperature changes can be introduced during these measurements either intentionally or as a result of some other process. The microwave cavity itself also has a temperature-dependent response, which can affect the results. A common method to correct is to use another resonant mode separately to the measurement mode, which is not affected by the sample. Instead of using independent modes, this paper describes a method to use split degenerate TM m 10 modes of cylindrical cavities. TM m 10 consists of two modes with identical field patterns with a relative rotation between them and identical resonant frequencies. A strategically placed perturbation reduces the frequency of one of the TM m 10 modes and affects the coupling of both modes by reconfiguring the fields. This can be used for temperature correction by placing a sample such that both modes are equally coupled. The lower frequency, the perturbed mode is used as a measurement mode. The higher mode is used as a reference for temperature correction as it is unaffected by the sample. This technique was verified by measuring the permittivity of pure water using an aluminum microwave cavity resonator at 3.96 GHz. The temperature was swept between 20 °C and 60 °C, and the results was verified against the literature.

A new cavity-based method to measure the complex permittivity of dielectric materials is presented here. The method uses a double-ridged waveguide for the cavity instead of the widely used rectangular waveguides, thus enhancing the operational frequency bandwidth by twofold. The bandwidth enhancement is advantageous when measuring the permittivities of frequency dispersive specimens. Building on the perturbation theory, this paper develops the measurement equations required for permittivity extraction. The measurement errors induced by the approximations in the perturbation theory are evaluated using numerical simulations, and the errors are quantified for different specimen sizes and dielectric constants. The experimental results are also presented. The complex permittivities of three common plastic specimens are measured at frequencies of around 3, 5, and 8 GHz using one double-ridged cavity. For comparison purposes, the same samples are also measured using two rectangular cavities operating in the S- and X- bands. Good agreement in the measured permittivity values is observed.

A method that allows the determination of magnetic permeability in magnetic bodies, as well as the ferromagnetic resonance (FMR) linewidth, by measuring only the quality factor and the resonant frequency of the perturbed microwave cavity at FMR is presented. The method is based on a set of equations derived for various types of magnetic media, including ferrites, single crystals, and polycrystalline materials. The evaluation of resonators containing magnetic medium is considered, and a detailed description of the spectrometer and the experimental procedure are presented. Independently measured yttrium iron garnet samples were used to validate the method.

Detection and removal of undesirable objects is an important issue in many material processing industries. This paper presents a microwave-based measurement technique for detection of dielectric objects in powder materials flowing through metal pipes. A nonintrusive microwave sensor is developed, which uses multiple resonant modes to obtain high sensitivity with respect to permittivity variations inside the pipe. Undesirable objects are detected based on the scattering parameters of the sensor, which are measured using a fast-sampling microwave transmitter and receiver unit. We present a detection algorithm derived from the likelihood-ratio test, which includes a parametric model of the local statistical distribution of the measured scattering parameter data. The model involves a set of Mobius transformations that map the measured scattering parameters to a domain where the data are Gaussian distributed. All unknown parameters in the model are estimated from data using maximum likelihood. Based on measurement results from a gravity-fall experimental setup, we conclude that small dielectric objects can be reliably detected in heterogeneous flows of dielectric powder.

This paper presents a new method for calculating the cavity modes of cylindrically symmetric cavities and applies the method to stacked dielectric resonators (DRs) inside a conducting cylindrical shell. The modes of an arbitrary cavity are expressed using an eigenfunction expansion, the basis functions being the fields of an empty cavity. The wave equation for the electric displacement field, $D$ , can be manipulated to eliminate derivatives of the discontinuous dielectric constant and provide an eigenvalue equation for the resonant frequencies of the cavity. The eigenvectors specify coefficients of the empty cavity modes that sum to compose the electric and magnetic fields. A test against theory is presented for an infinitely long dielectric cylinder inside an infinitely long cylindrical cavity, and the accuracy is better than 0.4% for nearly all modes. The calculated resonant frequencies of the quasi-TE011 (TE $_{{\mathrm {01\delta }}}$ ) mode are also compared with the experimentally measured frequencies of resonant cavities containing DRs for ten different configurations; the results display an accuracy of better than 1.0% in all but one case. A link to a MATLAB implementation of the technique is provided.

Two sets of experiments are described. In the first set, the ultraviolet (UV) radiation created by the spark channel is passing through the wire mesh to illuminate the structure in the resonant cavity. The UV radiation creates many radiation lines in the photoionized plasma. The current flowing in the resonant cavity is also measured. The radiations exiting the cavity are compared with the data obtained in the atomic hydrogen maser. In the second set of experiments, the spark channel discharges are formed inside the resonant cavity. When the resonant cavity was tuned to $\approx 1$ GHz, the objective is to learn why the system gives almost the single $\approx 1$ GHz radiation line at the output under certain conditions. The study indicates that the basic mechanism of microwave generation in atmospheric air is the microwave amplification by the stimulated emission of radiation.

We demonstrate a dedicated design of microwave cavity resonators mainly developed for high-throughput phenotyping systems of plants. Based on simulations, the field distribution of the TM010 mode inside the resonators was modified to achieve an electric field, which is homogeneously distributed in the horizontal plane and oriented in the vertical direction. Such a distribution together with large openings on top and bottom of each cavity allows to measure volumetric and dielectric properties of material that is widely distributed in space, such as plants with varying shoot branching and architecture, with no need to know its 3-D position inside the resonator. A theory was developed based on an equivalent RLC parallel circuit, showing excellent agreement with the experimental findings. For maize leaves taken as an example, it was shown that the resonator systems allow to perform precise measurements of water distribution in plant tissues.

Methods of gyrotron electron beam diagnostics developed at St. Petersburg Polytechnic University are reviewed. Bremsstrahlung X-rays produced at the collector can be used for definition of electron energy distribution in the spent beam. This possibility has been tested at two megawatt-power-level gyrotrons at the Karlsruhe Institute of Technology. Analysis of propagation of gigahertz-frequency signals in a slow-wave structure coupled with the beam can be used for the determination of velocity characteristics upstream from the microwave cavity. Numerical simulations performed with CST Particle Studio confirmed that data on axial component of electron velocities can be derived from frequency dependences of the slow-wave gain. Control of electron beam quality via tuning of the electric and magnetic field distributions provides a promising instrument for gyrotron efficiency enhancement.

A systematic study of the electrodynamic coupling between the ferromagnetic resonance (FMR) and the cavity mode of a microwave cavity is presented. The nature of the FMR and cavity modes, described by their resonance position and line width, is measured and compared with a classical model based on the Landau–Lifshitz–Gilbert equation and an RLC circuit, which explicitly implement Faraday’s and Ampere’s laws. The relationship between the coupling gap, which can be accessed experimentally, and the coupling strength, which is a fundamental property of the FMR/cavity system, is discussed on the basis of this model. A straightforward method is experimentally developed to control the coupling gap. The capability of using such a tunable cavity-FMR coupling in combination with spin pumping could provide us with new technologies that utilize the light-matter interaction to control spin current in cavity spintronics.

The microwave pulse compression procedure consists of excitation of a working mode in a resonant cavity and transforming the mode into an auxiliary one that is coupled to an output line. Both transforming and coupling involve switching. Transients were calculated by recursion relations giving higher accuracy at short time constants. Demonstration experiments were run in the X-band. The compressor prototype showed power amplification of 15 dB at an output pulse width of 2.7 ns and a peak power of 1.5 MW. Mode transformation efficiency approached 0.7. A sequence of nanosecond and sub-nanosecond microwave pulses within the length of an input feeding pulse can be, in principle, obtained.

The 2015 Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium in Phoenix, Arizona, played host to a total of 16 student design competitions. One of these, sponsored jointly by the MTT-12 Technical Committee on Microwave and Millimeter-Wave Packaging and Manufacturing and the MTT-8 Technical Committee on Filters and Passive Components, was based on the design of a substrate integrated waveguide (SIW) dual-band filter.

This letter describes the development and implementation of an impedance-matching (IM) method for achieving optimal power transfer efficiencies (PTE’s) in cavity resonator wireless power transfer (WPT) systems. Specifically, we develop a bandpass filter (BPF) circuit model and utilize network analysis to predict and realize maximum achievable PTE to miniature systems enclosed within a hollow metallic cylindrical cavity excited in ${\rm TM}_{010}$ resonant mode. Measured PTE results are demonstrated matching closely with the developed theory and circuit simulations. We achieve a peak PTE of 33% to a 5-mm-diameter receive coil that occupies a volume that is $5.23 \times {10^6}$ times smaller than the volume of the cylindrical cavity. Our achieved PTE is 4 times larger than the PTE achieved to a system with no optimal IM network but only a single resonant capacitor connected in series with the receive coil. The model and results presented illustrate our optimal design methodology for realizing maximum achievable PTE in cavity resonator WPT systems.

The regeneration of soot filter using microwave heating has several drawbacks, which include non-uniform regeneration, ineffective on very small soot thickness, and could lead to excessive heating, which damages the filter that is loaded with high layer of soot. This paper proposes a novel technique for localized rapid heating and oxidation of any thickness of solid soot, and saving of the consumed microwave energy. This technique was applied by inserting a metal in the accumulated soot, located inside a closed multi-mode microwave cavity, attached to a mono-mode waveguide, connected with a magnetron with a capacity of 2.45 GHz and 800 W. The electric field, generated heat, and temperature variation with time till the attaining of the oxidation temperature of the soot during microwave heating were simulated. The simulation methodology is based on the concept of electromagnetic-thermal energy conversion by coupling Maxwell with heat transfer equations. Finite element method was used with frequency domain for electromagnetic analysis and time domain for thermal analysis. In agreement with experimental results, the predicted microwave heating time to attaining the soot ignition/oxidation temperature was reduced from 8.5 to 0.3 seconds. Based on the presented technique, metallic electrodes can be inserted on the soot filter surfaces as local heating electrodes to enhance the microwave heating of the soot filter regeneration.

We explore a novel concept for pulse compression scheme applicable at RF, microwave, and possibly up to optical frequencies based on structured energy distribution in cavities supporting degenerate band-edge (DBE) modes. We show the high spatial concentration of energy due to DBE modes and proper choice of boundary conditions in coupled transmission lines (TLs) provide the basis for superior performance of the structured cavity when compared to a conventional cavity. We investigate the novel cavity features: larger loaded quality factor of the cavity and stored energy compared to conventional designs, robustness to variations of cavity loading, energy feeding and extraction at the cavity center, and substantial reduction of the cavity size by use of equivalent lumped circuits for low-energy sections of the cavity. Structured energy also allows for controlled pulse shaping via engineered extraction techniques. The presented concepts are general, in terms of equivalent coupled TLs, and can be applied to a variety of realistic guiding structures. Potential applications include microwave pulse compression devices, on-chip millimeter-wave pulse generation, and pulsed laser generation.

Magnetodielectric (MD) materials find application in many areas of microwave engineering, and therefore, measurement of their dielectric and magnetic properties is very important. This paper presents a novel MD material characterization method using the cavity perturbation technique (CPT) with substrate-integrated waveguide (SIW) cavity resonators. Frequency dependent complex permittivity and permeability of MD material can be extracted with a single SIW cavity structure by inserting the sample material into different locations. The fundamental theory of CPT is explained and its analysis for SIW cavity is discussed. Cobalt nanoparticles are synthesized with a fluoropolymer matrix to realize the MD materials and their properties are measured in the frequency range 1–4 GHz. The effect of volume fraction and density of the synthesized MD materials on the dielectric and magnetic properties has been studied.

This paper presents an original passive microwave substrate integrated cavity resonator [substrate integrated waveguides (SIWs)] as an environment sensor for humidity detection. The proposed structures are based on a high quality factor $(Q\sim 300)$ substrate integrated cavity resonator operating at 3.6 and 4.15 GHz. The detection principle is based on a frequency shift due to the permittivity variation of the humid air. This variation can be detected and used as the sensor indication. The frequency shift has been estimated analytically using the dielectric perturbation method for the resonator prototypes. The structure of the presented SIW resonators has been tested in the presence of humidity and shows sensitive characteristics in the range of 0%–80% relative humidity in accordance with the proposed model. A comparison of sensitivity performance between the new structure and other reported microwave components for environmental sensing is also presented. Measurements of repeatability and reliability for the proposed structure are discussed as well. As a new microwave component type, the proposed substrate integrated environmental sensor has the advantage of providing a new fabrication solution for radio frequency environmental sensing and greatly simplifies the sensor's manufacturing processes and cost.

This paper proposes a novel diplexer based on triple-mode dielectric-loaded cylindrical cavities. Such two metal cavities are designed to achieve two different frequency bands, while three resonant modes of a single cavity are classified as a TM mode and a pair of hybrid (HE) degeneration modes. An off-centered dielectric resonator instead of a traditional corner cuts perturbation or screws perturbation properly perturbs the two degenerate modes in the same cavity. Extensive study is then conducted to design this proposed diplexer. Finally, a diplexer prototype is fabricated using a brass cavity and it is tested for experimental verification of the predicted results. Good agreement between measurement and simulation is achieved.

Both thickness and sheet resistance of conductive nanomaterial deposited on glass substrate have been simultaneously measured using the TE011 mode cavity method. Measurements have been performed in two cavities with resonant frequency of ~10.8 and ~17.7 GHz, respectively. Measurement errors of thickness and sheet resistance can reach below 10%. Compared to existing methods, the presented method does not require prior knowledge on either film thickness or conductivity; what is more, by using the film as one of the end plates of the cavity, this method is noncontact and has little requirements on sample shape. These advantages suggest that the presented method has potential to be used in situ of monitoring the metal film characteristics such as that in microelectronic fabrication industry.

In this letter, a millimeter-wave filter constructed by 3-D substrate-integrated circular waveguide (SICW) resonant cavity is numerically and experimentally investigated. The 3-D SICW with the sidewall structure of via fences and circular pads is fully integrated in a low-temperature co-fired ceramic (LTCC) substrate. The fundamental mode (quasi-TE111 mode) of 3-D SICW cavity and the TE130, TE140 modes of overmoded substrate-integrated waveguide cavity are adopted to form the fourth order bandpass filter. Compared with the traditional planar structures, the spatial configuration can enhance the microwave performance of the device and brings more flexibility for the system design. The measurements of the fabricated filter show that the insertion loss is less than 1.9 dB at 174 GHz and the relative bandwidth is about 13.8%, which is in good agreement with electromagnetic simulations.

A three-step unconditionally stable locally 1-D approach is proposed, representing a dispersive anisotropic magnetized plasma medium. The accuracy and stability of the method are verified through simulation of wave propagation in a microwave cavity partially filled with a plasma slab. Finally, Faraday rotation across a plasma slab is simulated by the proposed method.

A triple-mode wideband bandpass filter (BPF) is proposed. It consists of a single rectangular waveguide cavity with two small metal rods to be inserted into the cavity from input/output feeding ports. As such, one TM110 mode, one TM210 mode, and one TM130 mode can be simultaneously excited in this cavity to form up a wide frequency passband. The fractional bandwidth is 58% at center frequency of 5.5 GHz with low insertion loss (

This article reports on a simple yet efficient miniaturization technique of substrate integrated waveguide cavity resonators through stub loading. The stubs are attached to the cavity side edges and they are coupled with the magnetic fields of the cavity. This setup allows the stub loaded cavity to operate below its fundamental resonant frequency. This miniaturization technique is demonstrated by developing a two pole filter in horizontally and vertically coupled configurations. The potential to incorporate electronic tuning and various possible applications of these miniaturized cavities in low frequency system-in-package designs make them an excellent choice as compared to their conventional counterparts.

The majority of existing wireless power solutions are capable of 2-D surface charging of one or two devices, but are not well suited to deliver power efficiently to large numbers of devices placed throughout a large 3-D volume of space. In this paper, we propose an unexplored type of wireless power transfer system based on electromagnetic cavity resonance. Here, we use the natural electromagnetic modes of hollow metallic structures to produce uniform magnetic fields which can simultaneously power multiple small receiver coils contained almost anywhere inside. An analytical model is derived that predicts the coupling coefficient and power transfer efficiency from the cavity resonator to a small coil. These predictions are verified against simulated results with a coefficient of determination of 0.9943. By using two resonant modes, we demonstrate that a 3-in diameter receiver can be powered in nearly any location in a 140 cubic foot test chamber, at greater than 50% efficiency. Additionally, we show that ten receivers can be powered simultaneously and that this system is capable of recharging consumer electronics such as a cell phone.

Different designs of multichannel resonant microwave pulse compression systems operating in $X$ - and $S$ -bands are described. The output pulsed microwave power of these systems is expected to be severalfold greater than that of compression systems with a single output channel. These compression systems can be used as compact sources of high-power nanosecond-duration microwave pulses, sources of synchronized sequences of microwave pulses, and sources for development of phased arrays of compressed microwave pulses. In particular, the authors describe the characteristics of a two-channel $S$ -band resonant microwave pulse compression system with nanosecond-duration output pulse and an output pulsed microwave power of 1 GW. The operation of a four-channel $X$ -band compression system with a possible eightfold output pulsed microwave power increase, relatively to the microwave power in the cavity, is also described. The design of an eight-channel system with a 16-fold output pulsed microwave power increase is reviewed. The parameters of an $X$ -band compression system with multichannel output unit formed as a set of interference microwave switches extracting the energy in synchronism are presented.

The applications of magnetic composites in electromagnetic shielding, resonance imaging, and biomedical drug research are growing rapidly. Therefore, there is a huge demand to characterize these materials in order to obtain their dielectric and magnetic properties in the microwave frequency range. In this paper, a novel rectangular cavity method is proposed to obtain the complex permeability and permittivity of the test sample placed in the $E$ -plane of the rectangular cavity. The proposed method eliminates the need of physical relocation of a specimen in the $H$ -plane, which is usually required in the case of presently available methods to characterize the magnetic samples. The closed-form formula for this unified approach is developed from the first principle, and is later modified to consider some practical consideration. The proposed method is first numerically tested and verified for various standard samples, where the data are taken from the literature. Thereafter, the $X$ -band rectangular cavity is designed and fabricated to measure a number of available samples. The significance of the proposed approach can be appreciated from the fact that even for finite-size samples, the permeability and permittivity can be extracted with the typical errors of 5% and 2%, respectively.

When several maser waves having different frequencies are generated in the resonant cavity, the interactions between these waves will occur via the so-called coherence effect. The objective of this paper is to show that the basic features of all the computed waveforms are governed by the linear interaction between the two dominant frequencies that are formed in the resonant cavity. These frequencies arise because the resonant cavity is not well tuned. Other frequencies present in the cavity can be treated as a linear addition to the interaction between these two dominant frequencies. The line at 1.420 GHz is due to the atomic hydrogen maser action.

A TM010 mode cylindrical cavity is employed as the main sensing element to characterize variable density compositions of material streams, for example, paper, textile fiber, or plastic composites. Through-passage holes at both end plates in the middle of the resonator frame provide for the material flow, hence forming a cylindrical channel region that is isolated from the cavity by a thin dielectric insert tube to avoid contamination of the cavity. In relation to the cavity dimensions, the hole size is relatively large to accommodate material flow variations in volume or mass density. The large through-hole geometric feature causes the electric field uniformity to be compromised within the channel region. As a consequence, unwanted frequency shift responses occur due to lateral movements in the material stream. A study related to the electric field homogeneity of a cylindrical cavity is presented. It is shown that the field homogeneity can be improved by placing a tubular dielectric insert inside the cavity. The main aim is to optimize the shape profile and select a feasible material for the dielectric insert. The evaluation of the electric field homogeneity is based on the measure of electric field variations within the channel. Dielectric inserts with conical profile are presented as an improved alternative to cylindrical tubes for uniform field homogeneity inside the sensing region.

We have coupled a tapered optical microfiber to a translatable thin-film lumped-element superconducting Al microwave resonator that is cooled to 15 mK. The thin-film resonator has a resonance frequency of 6.14 GHz, a quality factor of Q = 2.59 × 105, and is mounted inside a 3-D Al microwave cavity that provides a well-isolated electromagnetic environment. The microfiber is held fixed while the cavity is mounted on an x-z translation stage that allows the lumped-element resonator and the optical fiber to be brought close to each other (less than 1 mm). When 780-nm light is sent through the fiber, Rayleigh scattering in the fiber causes a weak position-dependent nonuniform illumination of the thin-film resonator, exciting quasiparticles in the superconducting film and thereby affecting its resonance frequency f o and Q. We report on the response of the resonator to both the scattered optical power and the presence of the fiber's dielectric, as the thin-film resonator is moved in situ with respect to the fiber.