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In this article, an investigation has been performed to analyze the role of hollow cathode aperture wall profile on pseudospark (PS) discharge-based single gap sheet electron beam source. A simulation study using COMSOL Multiphysics has been carried out for different hollow cathode aperture wall profile parameters, such as thickness and radius of curvature of aperture wall. The role of hollow cathode aperture wall thickness “ $t$ ” and the radius of curvature of aperture wall “ $R$ ” for different gas pressures, 16–20 Pa, and the corresponding applied gap voltage 16–20 kV have been studied. The hollow cathode aperture wall thickness has been analyzed for the range of ~1–3 mm, keeping the constant aspect ratio 12:1, while the radius of curvature of aperture wall has been analyzed for the range of 0–3 mm for different wall thicknesses. Experimental studies have also been performed to analyze the role of the thickness of the aperture wall on PS discharge. A good correlation has been obtained between the simulation and experimental studies.

A miniature planar meander-type slow-wave structure (SWS) for a W-band traveling-wave tube is studied. Computer simulation of the SWS electrodynamic parameters is performed. A new technology for fabrication of planar microstrip SWSs with the aid of laser ablation is proposed. The S-parameters of the SWS are experimentally studied. The experimental data are in good agreement with the results of the 3D computer simulation. Output characteristics of the traveling-wave tube with a sheet electron beam and planar SWS are calculated.

A vircator-based microwave oscillator with a nonlaminar electron beam and an extended matched section of a helical slow-wave system was studied numerically and experimentally. It is shown that the oscillator efficiency in the frequency range of 1–3 GHz reaches 20%.

We present the results of experimental investigation of a laboratory prototype of the electron-wave microwave amplifier for the case of great values of the inhomogeneity parameters of electron beam velocities. The influence of several factors on the gain of such systems in the case under consideration is demonstrated experimentally. It is found that at great values of the inhomogeneity parameters a significant increase in the power of the input signals leads to an increase in the gain of the system. The proposed scheme of operation of the electron-wave amplifier allows improving its stability, increasing the gain to about 20 dB, and reducing its size. The significance of the obtained experimental results and studied phenomena for advancement of the operating frequencies of electron-wave amplifiers into a shorter-wavelength band is shown.

Application of higher harmonics generation mode in a compact low-voltage vircator-type vacuum electronic device utilizing nonlaminar electron beams operating in millimeter band is considered and preliminary experimental results are reported. Higher harmonics generation was achieved by formation of translaminar electron layer through the choice of the optimal voltages for the control electrode and electron beam inhibition by the electrostatic field of the collector. This approach allowed for dense electron grouping in nonlaminar electron beams that provided the growth of the amplitude of the higher harmonics in the output power spectrum. In this system, the increase of the fundamental operating frequency by application of external magnetic field was experimentally demonstrated. If combined with higher harmonics generation mode, this can lead to significant increase of resulting operating frequency of the compact low-voltage system to millimeter wavelength band.

In this paper, we present the results of design and development of the multiple-tunnel meander-line slow-wave structure (SWS) for a high-power traveling-wave tube (TWT) with multiple sheet electron beam operating at millimeter band. Electromagnetic parameters of the SWS with different number of beam tunnels are simulated. The results of 3-D PIC modeling of small-signal and large-signal hot-test operation are presented. Technologies for fabrication of the multiple-tunnel SWS are discussed.

The results of fabrication and cold-test study of the slow-wave interaction structure for the V-band backward-wave oscillator with a pseudospark-sourced sheet electron beam are presented. The proposed interaction structure is comprised of a truncated sine waveguide with wideband-matched output couplers. The slow-wave structure is designed, simulated, and fabricated by CNC-micro milling. The results of characterization of the microfabricated SWS sample by the scanning electron microscopy and stylus profilometry technique are presented. Preliminary results of experimental studies of electromagnetic parameters and their comparison with the numerical simulation are presented. The electron gun providing a high-current-density pseudospark sheet electron beam is also developed.

Results of experimental study of the reflection and transmission losses in the V-band of µm-thick Si-Al films on the dielectric substrates are considered. Two sources magnetron co-sputtering deposition of Si-Al alloys was utilized to prepare a series of coatings of varied chemical composition and thus different properties. Control over films composition was provided by variation of Al magnetron power source with constant Si magnetron power source. Segregation of Si and Al atoms in Al-Si films was observed at a specific power of Al magnetron source during the deposition: Si atoms were mainly concentrated at the lower levels of the film adjacent to the substrate, while Al atoms tended to concentrate near the upper surface of the coating. Distinct electromagnetic properties of Al-Si films fabricated at the transient phase of segregation mode were observed: one side of the film demonstrated low reflection in the millimeter-band while almost full reflection was observed from the other side. Such properties of µm-thick Si-Al films upon dielectric substrates can be useful for development of millimeter-wave antenna modules technology.

Flexible electronics attract great interest due to their wide opportunities for practical application in the field of wireless communication, personalized medicine, security, etc. Flexible wireless technologies require low profile, lightweight, and compact antennas. In this work, an antenna on a flexible dielectric substrate for the ISM range and 2G/3G/4G standards of cellular bands was designed and numerically studied. Also, we plan to fabricate the designed antenna with the help of our original technological approach based on the magnetron sputtering and nanosecond laser ablation. Several preliminary results of microfabrication opportunities with the help of the mentioned above approach are shown.

In recent decades, there has been a steady trend towards the miniaturization of electronic devices, and their key components. Fabrication of such microsized devices and their key part is a real challenge. One of the well-known methods of microfabrication is laser ablation based micromachining. In this work, we study the peculiarities of the influence of nanosecond laser pulses on thin copper films on dielectric substrates. The main aim of this work is to reveal the effective regime of nanosecond ablation of the copper thin film with different thicknesses. The deposition of a copper thin film on the dielectric substrate was carried out by magnetron sputtering. Glass slides were used as dielectric substrates. To quantitatively describe the interaction of a thin copper film with laser pulses of nanoseconds duration, the fluence was calculated taking into account the velocity of the laser spot. The threshold of fluence that needs to effectively ablate the rectangular region of the copper film with a certain thickness was revealed. The obtained results will be used in the future in precision microfabrication of planar electromagnetic structures for vacuum electron devices operating in millimeter-wave bands.

Results of research aimed at the development of traveling-wave tubes (TWT) with multiple sheet electron beam at short part of the millimeter band are presented. The designs of the double-tunnel meander and double grating slow-wave structures (SWS) are studied. Electromagnetic parameters of the SWSs are simulated. The results of 3D PIC-simulation of TWT performance in linear and nonlinear operating modes are presented. Technologies for microfabrication of the SWSs are discussed.

Design and preliminary numerical simulations of D-band planar microstrip meander-line slow wave structure for lowvoltage tubes with sheet electron beam were carried out. An original approach based on magnetron sputtering and laser ablation methods was utilized for microstrip meander-line slow wave structure microfarication. An application of nanosecond and picosecond laser ablation for microfabrication of D-band (110-170 GHz) planar microstrip meander-line slow wave structure was considered. We have verified our original approach for planar slow wave structures microfabrication by using different CNC precision laser machines operating with different values of laser pulse duration (100 ns, 8 ns, 4 ns and 10 ps). Samples of slow wave structures were fabricated and characterized by scanning electron microscopy and profilometry methods. It was shown that each considered CNC precision laser machine allows fabricating D-band microstrip meander-line slow wave structure with required dimensions, but picosecond laser ablation has such advantages as the absence of ablation products (droplets, and etc.) on the slow wave structure surface. As the next step, we are going to study S-parameters of microfabricated D-band microstrip meander-line slow wave structure samples experimentally by using vector network analyzer with D-band frequency converters.

We consider the results of dielectric properties study in millimeter band of thin-films based on silicon nitride compositions. Silicon nitride thin-film coatings were deposited on a substrate by DC magnetron sputtering. As a substrate for silicon nitride thin-film coatings a quartz plate were utilized. The ratio of argon and nitrogen in the working gas mixture was chosen as the variable parameter to control the composition of the deposited thin-film coating. Several samples of silicon nitride thin-film coatings with about 1 um thickness were fabricated. Radiophysical and dielectric properties of the fabricated SiN-type thin-film coatings were studied in millimeter wave frequency band of 50-70 GHz (V-band) with help of free space measurement method. The obtained results have shown that by controlling the resistive thin-film coating composition one can only slightly vary the radiophysical and dielectric properties of coating in millimeter-band.

In this paper, we consider a short review of existing technologies of flexible antenna fabrication and propose our original approach for flexible antenna fabrication. Review of existing technologies of flexible antenna fabrication includes photolithography, screen printing, pad printing, gravure printing, inkjet printing, micro-dispensing, micro-jetting, and aerosol-jet technology. Advantages and disadvantages of each mentioned above technologies were noted. In the second part of this study, we consider our original technology for antenna fabrication on flexible substrates utilizing magnetron sputtering and laser ablation methods. Samples of flexible antennas are formed on a flexible dielectric substrate in a technology process comprising following basic stages: 1) deposition a conductive coating onto the dielectric substrate with help of magnetron sputtering, 2) formation the pattern of the antenna structure on the conductive coating by laser ablation. In the final stage, the substrate is divided into individual samples of specific sizes. A number of test flexible antennas fabricated by our original approach are shown.

Slow-wave structure (SWS) is a core part of a traveling-wave-tube (TWT) amplifier. In this letter, the planar microstrip meander SWS on a dielectric substrate at $V$ -band (50–70 GHz) is studied. The basic electromagnetic parameters of the SWS are calculated. The SWS circuits are designed and fabricated, and good transmission characteristics are measured. The SWS developed is characterized by a wide bandwidth and a relatively-large slow-wave factor, and is suitable for a low-voltage TWT with the sheet electron beam.

Ongoing active development of modern radio frequency electronic devices operating in the millimeter (V) band, such as fifth-generation wireless communications, demands new materials to control electromagnetic interference, compatibility, and reliability of such systems. This work investigates feasibility absorptive non-reflective thin coatings deposition on dielectric substrates using simultaneous magnetron co-deposition. For this, electromagnetic waves propagation in the millimeter band through in micrometer-thick Al–Si films of varied composition was studied. The co-deposition process was controlled by the ratio of sputtered atoms fluxes. Graded segregation was observed under certain parameters of the co-deposition process, resulting in a depth gradient of an aluminum content, as confirmed by the secondary ion mass spectrometry study. A qualitative model was proposed involving aluminum-induced silicon recrystallization happening in the course of a known aluminum interlayer exchange process. The observed Al–Si segregation effect in micrometer-thick films allows for preparation of the non-reflective and absorptive material for operation in the V-band with reflection losses more than 10 dB and transmission losses around 5 dB in the bandwidth of up to 20 GHz.

We have considered a permutation entropy method for analyzing chaotic, noisy, and chaotic noisy series. We have introduced the concept of permutation entropy from a survey of some features of information entropy (Shannon entropy), described the algorithm for its calculation, and indicated the advantages of this approach in the analysis of time series; the application of this method in the analysis of various model systems and experimental data has also been demonstrated.

Formation of electron bunches in turbulent electron beams is numerically simulated and experimentally studied. A prototype of a laboratory generator is proposed, and control parameters (in particular, electron spread with respect to longitudinal velocities and additional deceleration of electron beam by electrostatic field of collector) that affect the characteristics of electron bunches and provide an increase in the number and amplitude of higher harmonics in the output spectrum are determined.

We present results of a theoretical and experimental investigation of the output characteristics of transparent (containing no local absorbers) traveling-wave tubes (TWTs) operating on multivelocity (turbulent) electron beams. It is established that higher gain (up to 20 dB) and higher efficiency (40–50%) can be achieved in this case in comparison to the output characteristics of transparent TWTs employing monovelocity (laminar) electron beams. This effect is explained by the formation of space-charge bunches of much higher density in multivelocity electron beams than in monovelocity beams.

In this paper, we deal with the study of flexible antennas for ISM range fabricated by our original approach based on magnetron sputtering and laser ablation. We used polyimide film with a thickness of 100 |xm as a flexible dielectric substrate. As a conductive layer we used oxygen free copper and nickel. We used a known sketch for the antenna with a coplanar feeding structure that has already numerically verified, fabricated by the inkjet printing technology and experimentally studied. We have fabricated several flexible antenna samples with coplanar feeding structure using our original approach. Results of scanning electron microscopy and optical microscopy studies of fabricated flexible antennas were considered. Antennas measurements were carried out with the help of an experimental setup based on the vector network analyzer. The experimental measurements were preceded by 1-port type calibration procedure in 0.3-3 GHz band on coaxial ends of cables using automated electronic calibration module. A comparison of obtained experimental results with the already known results from several scientific papers was considered. Fabricated antennas demonstrate reflection loss not worse than 16 dB throughout full ISM band (2.4-2.5 GHz). Obtained experimental results are in good agreement with the numerical ones and other published experimental studies.

We consider further development of our original technology for microfabrication of millimeter-band planar microstrip slow-wave structures (SWS). The technology is based on magnetron sputtering and laser ablation methods. V-band (50-75 GHz) and W-band (75-110 GHz) SWSs are fabricated and characterized by scanning electron and optical microscopy. Electromagnetic parameters of the developed SWSs are studied by numerical simulation and cold-test measurement. We have also carried out preparations and preliminary technological steps for the microfabrication of D-band (110-170 GHz) planar microstrip slow-wave structures.

In this work, we present the results of the numerical optimization of volume free-electron laser based on the interaction between an electron beam and periodic structure of microwave photonic crystal. The optimization aims at the advancement of such device to the sub-terahertz frequency range. We show that the reduction of characteristic geometric dimensions allows increasing the working frequency of photonic crystal fundamental mode up to 12.5 GHz. Moreover, we observe the possibility to generate microwaves at the fifth harmonic of the fundamental frequency, namely f=62.5 GHz and obtain an output power level of about 3.6 kW.

Experimental and numerical studies of an electrodynamic structure assembled according to photonic crystals’ principles placed inside a X-band rectangular waveguide are considered. Such structures are promising for microwave electronics (vircators, FELs, and etc.). Efficient excitation of high-order (and, hence, high-frequency) electromagnetic modes is one the most valuable features of dispersion characteristics of photonic crystal-like structures. The proposed electrodynamic structure is a 2D array of thin metal pins. Transmission and reflection characteristics of the proposed structure were measured experimentally and evaluated numerically in K, Ka and Q bands. The experimental results are in good agreement with the numerical ones.

We have propose an original approach for fabrication of flexible antennas for biomedical-related applications. The technology is based on magnetron sputtering and laser ablation methods. The magnetron sputtering method is used to deposit a thin layer of metal (copper) on a flexible substrate (polyimide film). Then laser ablation is utilized to remove excess copper thus forming an antenna pattern on the metal layer. ISM band flexible design with microstrip feeding structure was chosen for testing this technique. Results of numerical simulation are presented. A number of test flexible antennas were fabricated by our original approach. Similar flexible antennas were also fabricated via photolithography process. A comparison of the experimental results of return loss (S11) measurements of antennas with different fabrication approach was carried out. The obtained experimental data is in a good agreement with the numerical modeling results. Proposed technology has significant advantages in cost, speed, and flexibility over photolithography processes commonly utilized for such applications.

The results of the study of a microwave generator based on a nonrelativistic low-voltage vircator with a non-laminar electron beam and with an additional extended electrodynamics section are presented. An additional extended electrodynamics section based on the slow wave structure of helix type. It is shown that the proposed device has the efficiency of 20% with a frequency band of 1–3 GHz.

A traveling wave tube amplifier (TWTa) operating in V-band (62–65 GHz) was designed considering a planar slow wave structure (SWS). Particle in cell simulations were performed to calculate the gain and the output power of the TWT. The simulated TWT showed a maximum gain of 36 dB at 64 GHz and an output power of 16 W. The planar SWS was then fabricated with a laser machining technique. S parameters measurements of the SWS showed excellent matching and low losses in the operating frequency band.

Here we report on experimental and numerical investigations of an electrodynamic structure assembled according to photonic crystals' principles placed inside a X-band rectangular waveguide which is promising for microwave electronics. The features of dispersion characteristics of photonic crystals can be used for efficient excitation of high-order (and, hence, high-frequency) electromagnetic modes. In this work, the electrodynamic structure is a2D array of thin metal pins. Transmission and reflection of proposed system were measured experimentally and evaluated numerically. The experimental results are in good agreement with the numerical ones.

The influence of the magnitude and configuration of the magnetic field on the parameters of electron bunches formed in a multivelocity electron beam is analyzed. It is shown that the use of a cathode unshielded from the magnetic field and a nonuniform magnetic field increasing along the drift space enables the formation of compact electron bunches. The ratio between the current density in such bunches and the beam current density at the entrance to the drift space reaches 106, which results in a substantial broadening of the output microwave spectrum due to an increase in the amplitudes of the higher harmonics of the fundamental frequency.

The effect of the residual gas pressure on the spectral and amplitude characteristics of the output signal from the oscillator with the turbulent electron beam is examined. It is shown that ions resulting from gas ionization in the drift region promote formation of denser and more compact space charge bunches. Denser bunches increase the output signal power and aid in appearance of higher-order components in the spectrum, thus extending the working range to a higher-frequency region. When the device operates in the regime of noiselike signal generation, ions contribute to a decrease in the irregularity of the output power spectrum to about 0.3 dB in the working frequency range up to two octaves.

A generator of turbulent electron beams in an independent mode and in the mode of amplification of an external single-frequency signal is experimentally investigated. The formation of higher harmonic components in the spectrum of output radiation of the generator is shown experimentally. The phenomenological model of the turbulent electron flow is constructed on the basis of a chain of interacting “electron vortices” described by the modified nonlinear Van-der-Pol differential equations. The modes of independent dynamics and the mode of amplification of an external harmonic signal are considered. The results of numerical modeling and experimental investigations are compared. The qualitative correspondence of the behavior of the dependences obtained from the experimental investigation of the generator of turbulent electron beams and the results obtained from numerical modeling is shown.

We report the results of the design, simulation, fabrication, and cold-test measurements of millimeter-band 2D planar microstrip slow-wave structures (SWSs) on dielectric substrates. Such structures have a high slow-wave factor, which allows for low-voltage operation and reduction in the size and weight of the device. A low-cost and flexible fabrication technology based on magnetron sputtering and subsequent laser ablation has been developed and is reported in the paper. Microstrip meander-line SWS circuits at V-, W-, and D-bands have been fabricated and characterized. The fabrication of ring-bar planar SWSs by the photolithographic method is also discussed. Experimental measurement of S-parameters of the fabricated structures reveals good transmission properties. Return loss (S11) does not exceed −10 dB and attenuation is about 2 dB/cm in the V-band, 10 dB/cm in the W-band, and 8.5 dB/cm in the D-band.

Results of experimental studies on Si-W coatings fabrication by magnetron co-sputtering from two sources for electrodynamic structures in millimeter and submillimeter range of electromagnetic waves are presented. Control over sheet resistivity of the resulting coatings by varying the power of a magnetron with a tungsten target is demonstrated. Dependence of complex permittivity of Si-W coatings upon dielectric substrates on chemical composition in the frequency range of 50-70 GHz is studied.

Folded waveguide (FW) is a promising type of slow-wave structure (SWS) for millimeter-wave traveling-wave tubes. Results of development of several millimeter-band FW SWSs are presented. SWS circuits at Q- and V -band are fabricated by CNC-machining. Cold electromagnetic parameters of the SWS characteristics are simulated and reasonable agreement with the results of measurements is observed. Small-signal and large-signal gain is calculated.

A novel technology for microfabrication of millimeter-band planar microstrip slow-wave structures (SWS) is proposed. The technology is based on magnetron sputtering and laser ablation methods. V-band (50–70 GHz) and W-band (75–110 GHz) meander-line SWSs are fabricated and characterized by scanning electron and optical microscopy. Electromagnetic parameters of the developed SWSs are studied by numerical simulation and cold-test measurement. Small-signal and large-signal gain is calculated.

A novel technology for microfabrication of millimeter and THz band planar microstrip slow-wave structures (SWS) is proposed. The technology is based on magnetron sputtering and laser ablation methods. The magnetron sputtering method is used to deposit a thin layer of metal (copper) on a quartz substrate. Then laser ablation is utilized to fabricate a slow wave structure from the copper layer. V-band (50–70 GHz) meander-line SWSs were fabricated and characterized by scanning electron and optical microscopy. The proposed technology has significant advantages in cost, speed and flexibility over lithography processes commonly utilized for such applications. The future work will be aimed to expansion of the proposed technology to manufacturing of higher-frequency W-band (75–110 GHz) and E-band (110–170 GHz) planar SWSs.

In this work we report the results of numerical simulation and cold-test measurements of electromagnetic parameters of the V-band (50–70 GHz) meander-line slow wave structure. The microstrip meander-line slow wave structure is suitable for using in a millimeter-band traveling wave tube amplifiers. Several samples of copper microstrip meander-line slow wave structure on a quartz substrate consisting of 50 meander periods with input and output couplers were designed and fabricated. The slow wave structure was microfabricated by using our original and novel technology for microfabrication. The technology is based on magnetron sputtering and laser ablation methods. The magnetron sputtering method is used to deposit a thin layer of metal (copper) on a quartz substrate. Then laser ablation is utilized to cut a slow wave structure from the copper layer. This technique is a more facile, flexible and lower cost as compared to photolithography method. Transmission and reflection of microfabricated SWS were measured experimentally and calculated numerically. The results of the experimental cold-test measurements are verified by numerical simulations. Electromagnetic parameters of the slow wave structures were simulated using the finite-element ANSYS HFSS and COMSOL Multiphysics software packages. The results obtained with these two codes are in excellent agreement with each other and good agreement between experimental and numerical results is also observed.

We propose an approach for forming the dense bunches in turbulent electron beams with characteristics that promote the growth of the amplitude of the higher harmonics in the output spectrum. A design of microwave generator is also considered. The formation of translaminar electron layer by choosing the optimal voltages to the control electrode and an electron beam inhibition by the electrostatic field of the collector is used in the considered design of the generator. The above-mentioned factors create the necessary conditions for the formation of dense bunches of space charge of the electron beam. We have determined such control parameters as the spread of the electrons in the longitudinal velocities and the amount of additional inhibition of the electron beam by the electrostatic field of the collector, affecting the performance of electron bunches, and providing the growth of the number and the amplitude of the higher harmonic components in the spectrum of the output radiation. The previously obtained numerically simulated results are in qualitative agreement with the experimental data.