SPECTRAL PROPERTIES OF A RECTANGULAR WAVEGUIDE SECTION WITH A PAIR OF EQUAL-HEIGHT RECTANGULAR POSTS
L. P. Mospan, A. A. Kirilenko, D. Y. Kulik, S. A. Prikolotin
The identification of the physical phenomena that give rise to different resonance effects is the key to successful designing of the frequency-selective devices on their base. The investigation of the nature of the total reflection resonances formed by a waveguide section with a pair of rectangular posts arranged symmetrically in the cross section of rectangular waveguide was performed. The study presented was carried out in the frames of spectral theory of open waveguide resonators. The waveguide section was considered as a single-channel multi-mode resonator. Thus, the total reflection resonance was interpreted as a result of excitation of a number of eigen oscillations of the complex frequencies. Dynamics of their behavior in the complex plane was examined while the most important geometrical parameters, namely the distance between the posts and the gap under the posts, were varied. Comparative analysis of diffraction and spectral characteristics was performed. It was shown that the position of the resonance and its quality factor could be estimated by the complex frequency of one eigen oscillation. It was the eigen oscillation which was associated with the first higher mode of the section having the same symmetry as the fundamental mode of a rectangular waveguide. From a practical view obtained results make modelling the bandpass filters with complicated frequency responses possible.
MODE-MATCHING TECHNIQUE TAKING INTO ACCOUNT FIELD SINGULARITIES IN THE INTERNAL PROBLEMS WITH PIECE-WISE COORDINATE BOUNDARIES
PART 2. PLANE JUNCTIONS AND “IN-LINE” OBJECTS
S. A. Steshenko, S. A. Prikolotin, A. A. Kirilenko, D. Yu. Kulik, L. A. Rud’ and S. L. Senkevich
The generalization of the mode-matching technique in respect to the plane-junctions of lines with arbitrary piece-wise Cartesian coordinate of cross-sections and “in-line” objects of such lines is under consideration. The accuracy and efficiency of the new algorithms are demonstrated on the examples of various well-known 3D waveguide objects. Special cases of MMT application and upgrading the computational efficiency are discussed.
THE ALGORITHM FOR CALCULATION OF PLANE JUNCTIONS OF WAVEGUIDES WITH ARBITRARY CROSS-SECTIONS USING THE EIGENFUNCTIONS OF THE COMMON APERTURE
S. A. Steshenko
The mode matching technique is widely used for calculation of generalized scattering matrixes of waveguide steps. Its applicability is limited to the case where one waveguide section is fully inscribed into the other one. When the intersection of the two waveguide sections does not coincide with any of them, as a rule, a new “virtual” zero-length waveguide is introduced artificially between the two coupling waveguides so that the new waveguide steps satisfy the requirement of applicability of the mode matching technique. However, this approach requires three matrix inversions resulting in additional time expenses. In this paper we study the possibility of using the generalization of the mode matching technique to the case of coupling of waveguides with overlapping sections resulting in a matrix equation of the first kind. The two approaches are proven to be equivalent. Meanwhile the considered approach is shown to be more efficient than the traditional method introducing a “virtual” waveguide. The results obtained in this investigation will improve the efficiency of automated design systems for waveguide components based on mode matching technique.
TIME-DOMAIN MODELLING OF POWER COMBINING IN A PARALLEL CONNECTION OF STRIP LINES WITH GUNN DIODES
L. V. Yurchenko, V. B.Yurchenko
Development of compact high-power radiation sources for radiophysics requires power combining of active devices. Prospective devices for this purpose are GaN Gunn diodes. Simulation of power combining systems, particularly, those with time delay, shows a lack of relevant analysis methods and techniques, despite many achievements. In this work, using our modification of Dormand-Prince numerical method, we carried out time-domain modeling of nonlinear power combining in a distributed active system formed by a parallel connection of extended sections of strip lines with Gunn diodes specified by significant time delay of inter-device coupling. Complicated dependences of power output and period of oscillations on the system parameters have been found and investigated. The results emphasize an essentially nonlinear character of the processes and could be useful for the explanation of effects observed in practice. The model is efficient for the analysis of ultra-wideband field dynamics in active nonlinear systems with time delay. The research confirmed that oscillations in nonlinear, multi-element, time-delay active systems are poorly described by simplified models and require direct solutions in time domain.
DETECTION OF MOVING TARGETS BY MULTI-LOOK SINGLE-ANTENNA SYNTHETIC APERTURE RADAR
O. O. Bezvesilniy, B. A. Kochetov
Synthetic aperture radars (SAR) installed on aircrafts or satellites are able to obtain images of a scene with high spatial resolution. SAR data processing is a kind of optimal filtering of signals from static point scatterers. Signals received from moving targets are processed with the mismatched filter. It means that moving targets appear to be defocused and displaced from their true positions in radar images; therefore it is difficult to obtain information about moving targets from an ordinary SAR image. Nevertheless, the problem of detection of moving targets by SAR is important for many practical applications. One of the methods applied to solve the problem by using a common single-antenna SAR is based on multi-look processing, which consists in forming several image looks of the same scene patch from the data collected on different time intervals. The idea is that the static targets in the SAR image looks preserve their positions while the moving targets appear to be shifted, which allows distinguishing the moving targets from the static ones. Moreover, some motion parameters can be estimated via the target displacements. In this paper, formulas that describe the displacement of a moving target in SAR images are derived on the basis of the common equations of the multi-look SAR processing in time domain under the assumption that the target velocity vector is constant. It is found that in the framework of such approach one can determine the range to the target, the module and the radial component of the relative velocity vector of the target. In order to find true position of the target and its own velocity vector some additional information is required, for example, the target trajectory. Otherwise, the ambiguity between the target position and velocity is preserved. The obtained theoretical results are illustrated with computer simulations.
LARGE-SCALE DISTURBANCES IN THE EARTH'S MAGNETIC FIELD ASSOCIATED WITH THE CHELYABINSK METEORITE EVENT
L. F. Chernogor
Variations in the geomagnetic field components acquired during the Chelyabinsk meteorite event on February 15, 2013 and on reference days (February 12, 2013 and February 16, 2013) have been analyzed. The magnetometers chosen for study are located at Novosibirsk City, Alma-Ata City, Kyiv City, and Lviv City. The distance between the site of the meteor blast and a magnetometer varies from 1,200 km to 2,700 km. The passage and explosion of the Chelyabinsk meteor observed to be associated with the variations mainly in the horizontal component of the geomagnetic field. The magnetic field varied quasi-periodically with 30...40-min periods and 0.5...2-nT amplitudes for distances of 2,700...1,200 km, respectively, and with 2...3-hr durations. The horizontal velocity of the wave disturbances was approximately equal to 260...370 m s–1. A theoretical model of the wave disturbances has been developed. The model suggests that the geomagnetic field disturbances are caused by the acoustic gravity wave generated in the atmosphere by the falling meteoroid and associated with them traveling ionospheric disturbances. The calculated magnitudes of the wave disturbances are equal to 0.6...1.8 nT at distances of 2,700...1,200 km, respectively. The observations and the estimates are in good agreement.
INTERACTION OF PLASMA AND DEFECTIVE MODES IN ONE-DIMENSIONAL LAYERED PERIODIC DIELECTRIC STRUCTURES BORDERING UPON PLASMA-LIKE MEDIA
N. N. Beletskii, S. A. Borysenko, N. I. Gvozdev
The defective layered periodic structures (defective photon crystals), bordering upon plasma-like media (semiconductors and metals), arouse considerable interest. This is due to the fact that in such structures there are electromagnetic waves of different types. The properties of these waves have not been adequately investigated yet. The TM-electromagnetic waves in the one-dimension defective dielectric layered periodic structure, bordering upon a plasma-like medium, are studied in this paper on the basis of the numerical solution of the dispersion equation. The dispersion and energy properties of the plasma and defective modes are investigated depending on the location of the defective layer in the layered periodic structure. The effect of the resonant interaction of plasma and defective modes is predicted. The possibility for exciting electromagnetic waves in a defective layered periodic structure by the frustrated total internal reflection is shown. The results of investigations give some ideas of the nature of propagating electromagnetic waves in defective layered periodic structures and they can be used for developing new types of the waveguide structures used in up-to-date devices of signal processing in microwave and optical wave bands.
EXPERIMENTAL INVESTIGATION OF CLYNOTRON EFFECT IN THE DIFFRACTION RADIATION OSCILLATOR
M. Yu. Demchenko, V. G. Kurin, Ye. B. Senkevich
Nowadays there is no viable alternative for vacuum sources of continuous radiation in the THz range either of semiconductor lasers due to their low power (10–6 W), or among the lasers, which operate only at discrete frequencies. Among the existing vacuum sources of O-type the diffraction radiation oscillators (DRO) stand out for high frequency stability, narrow spectrum of the output signal, low noise and a wide range of electromechanical tuning and a relatively high level of output power. However, under the advancement in the THz range it is a problem of increasing of the DRO efficiency, which is connected with the need to ensure a high intensity of the high frequency (HF) field in the region of electron - wave interaction. The use of clynotron effect is one of the ways to solve the problem. The using of clynotron effects to enhance the interaction efficiency of the electron beam with a HF field in the DRO is discussed in this paper. Experimental study of the clynotron effect carried out in the DRO with additional (deflection) electrode, as well as in DRO, when the electron beam is entered into the interaction space through disperses bevels. It is shown that clynotron effects, the existence of which is due to non-removable fluctuations of the electron beam, accompany the interaction of the electron beam with the HF field. Increasing the ratio of the electron beam using cannot only reduce the starting current of the DRO, but also give higher generation power at low values of the magnetic focusing field.
GALLIUM NITRIDE DIODE WITH TUNNEL INJECTION
N. M. Goncharuk, N. F. Karushkin, V. V. Malyshko, V. A. Orehovskiy
Actual problem of modern micro- and nanoelectronics is advancing into submillimeter frequency range up to terahertz one. Inertia of carrier transfer processes is the main obstacle to increase operating frequency of available microwave diodes. Tunneling process presents the least inertia and noise level. In this work for the first time the diode on the base of single-barrier nanostructure with non-resonance electron tunneling and subsequent drift in transit layer has been investigated. The research was conducted in the framework of impedance small-signal model with considering delay time of electron injection, which is comparable with electron transit time of the diode. Dependences of diode microwave impedance in frequency range of its negative conductance on transit angle, diode diameter and parasitic resistance were investigated at different barrier layer parameters, which correspond to electron injection delay time from tenths up to more than one picosecond. It is shown, that the greatest negative conductance is reached at optimal values of transit angle and diode diameter at frequency close to the forth sub-harmonic of injection frequency. It exceeds considerably the frequency for resonance-tunneling diode (RTD) with comparable noise characteristics. This fact demonstrates the diode potential in microelectronics. The research can serve as a basis for making new type of sub-millimeter frequency range diode, which manufacture is considerably simpler than the same for resonance-tunneling one.
TRANSPORT OF HIGH-CURRENT TUBULAR RELATIVISTIC ELECTRON BEAM IN HYBRID COAXIAL MAGNETIC UNDULATOR
K. V. Ilyenko, T. Yu. Yatsenko, S. A. Kurkin
We formulate the closed system of dynamic equations, which describes the transport of high-current charged-particle beam in a coaxial drift-tube in combined longitudinal homogeneous (guide) and periodic undulator magnetostatic fields. The expressions for self-electric and magnetic fields of charged-particle beam averaged over the undulator period are obtained. The longitudinal component of the total self-magnetic field is also taken into account. We show that the guide magnetic field can be used to control the position of high-current charged-particle beam in the transverse cross-section of the coaxial drift-tube. It is also demonstrated that the presence of the guide magnetic field, which is usually considered necessary for an increase in the amplitude of the beam transverse oscillations and required for an enhancement of the output power in a hybrid coaxial free-electron laser/maser, also imposes a restrictive limit on the maximal value of the beam transmitted current.
V. N. Skresanov, Z. Е. Еremenko
The value of the complex permittivity of strongly absorbing liquids (e. g., water and aqueous solutions of various substances) needs to be known in various fields of science and technology, where such liquids are used. Previously, we proposed a waveguide-type measuring cuvette, which is a dielectric (quartz) cylinder immersed in the test liquid and developed a highly sensitive 8-mm band dielectrometer with such a cuvette. Theoretical and numerical analysis of the proposed cuvette was conducted without external border of the cuvette, which was the subject of discussion by comparing it with the experiment results. In this paper, we address this shortcoming, and conducted theoretical and numerical study of electrodynamics parameters of the dielectrometer cuvette with its external borders. This cell is formed by a circular metal 8-mm band waveguide with a coaxial cylindrical insertion of a low-loss dielectric. The study liquid fills the space between the surfaces of the insert and the waveguide. To increase the sensitivity of the cell to the changes in the concentration of substances in a test high loss liquid we used sufficiently thin layer of it (of the order of quarter wavelength), in which there is the interference of the waves. The result shows that the cuvette with the layer of absorbing liquid, wherein a penetration depth commensurate with the thickness of the liquid of the layer, has an increased differential sensitivity. The proposed structure has advantages when it is used in precise dielectrometer of strongly absorbing liquids compared with known technical solutions.
V. V. Yachin, V. K. Kiseliov, E. M. Kuleshov, P. K. Nesterov, T. L. Zinenko
A new recursive algorithm for the stable solution of the problem of electromagnetic wave scattering from multilayered periodical structure has been developed. The problem has been solved by the method of integral functionals. The comparison between the frequency response of reflection coefficients for carbon fiber reinforced plastic sample obtained by the method of integral functionals and by the method of polarization frequency reflectometry in sub THz frequency range at different incidence angles and polarizations has been conducted. These results can serve as a basis for the development of more complicated CFRP models including a simulation of different types of CFRP surface contaminations. It can help to interpret the reflectometry results in THz frequency range and improve non-destructive testing methods for carbon-filled plastics at this frequency range.