Nondestructive method of measurement of laminated plates dielectric parameters

The methods for measuring the parameters of dielectric materials of foil plates have been considered. It has been shown that for “non-destructive measurements” (i.e., without removing the metal foil from the dielectric plate), a method based on the excitation of electromagnetic oscillations in a rectangular plate considered as a resonator can be used. Based on the results of measurements of their resonant frequencies and Q-factors, the relative permittivity and the tangent of the dielectric loss angle of the material can be determined. The calculated relations obtained by the authors of the article in one of the early works using the electrodynamic model of a resonator with “magnetic walls” at the ends have been presented. The Q-factor of the resonator has been calculated by the perturbation method, taking into account the losses in the plate dielectric and metallization layers. The results of measurements for four samples from different dielectrics in the frequency range 200...1000 MHz have been presented. The experimental method has been described, in particular, the method of identifying the type of oscillation, the procedure for processing the measurement results. Due to the high sensitivity of the vector analyzer, measurements have been made with a possible small connection of the resonator (metallized plate) with the measuring circuit. This made it possible to minimize the influence of the coupling elements on the measured Qfactor of the oscillations and to consider this Q-factor close to its own. The presented results are in good agreement with the reference data for the materials. The conducted studies have shown the possibility of using a resonator model with “magnetic walls” at the ends for the analysis of electromagnetic oscillations in a foil dielectric plate and, accordingly, using the relations obtained in this case to determine the parameters of the dielectric plate. The conditions for using this model are the small thickness of the plate in comparison with its transverse dimensions and relatively low operating frequencies. The method, which is based on the calculated ratios of the electrodynamic model of the resonator with “magnetic” walls at the ends, provides a sufficiently high accuracy of determining the relative permittivity of the plate material, which led to the use of it (the method) in practice to control the parameters of foil dielectric plates intended for the manufacture of microwave and UHF-band microcircuits. The studies, the results of which have been presented in this paper, allow us to conclude that this method can also be recommended for determining the tangent of the dielectric loss angle of the plate material.

Dispersion distortions of wide spectrum signals during their propagation in the Earth ionosphere

The current trend in the development of radio engineering systems (RES) is to use wide spectrum signals, the application of which provides an increase in the resolution and secrecy of the radar operation, an increase in the speed and volume of transmitted information for communication and telemetry systems. The class of such signals includes ultrashort pulses (USP signals), radio pulses with linear frequency modulation (chirp signals). Also of interest are ultra-wideband (UWB) noise signals (UWBN signals), which have high electromagnetic compatibility, stealth and noise immunity. When designing promising ground-based and space-based RES using wide spectrum signals, an important task is to determine the distortions of their envelope shape and distortions of spectrum, as well as the change in the polarization of the emitted wave when passing through the Earth's ionosphere, since taking these distortions into account will provide conditions for optimal reception. This article presents the numerical assessment results of the expected distortions of the wide spectrum signals main types of the decimeter wavelength range, for middle latitudes at heights from 100 km to 1000 km. The conversion of the emitted pulse into a frequency modulated radio pulse is typical for the USP signal. For a chirp radio pulse with a monotonically increasing frequency, an initial decrease in duration with an increase in amplitude and subsequent stretching in time with further spread is typical (the amplitude change is estimated due to a change in the signal shape without taking into account spread). For a chirp radio pulse with a monotonically falling frequency and a UWBN signal, dispersion distortions manifest themselves as an increase in their duration with a decrease in amplitude. For all signal types under consideration that have passed through the ionosphere, a leading edge lag is observed, the dependences of frequency on time at an altitude of 1000 km are repeated and are close to hyperbolic character, the energy spectra envelope shape of the considered signals is almost not distorted. The polarization plane rotation for signals with a spectrum concentrated in the frequency range above 0.7 GHz does not exceed 45

Broadband wide-angle active phased L-band antenna array emitters

The purpose of this article is to review and justify the choice of emitters for constructing energy-efficient high-performance broadband active phased L-band antenna array with wide-angle scanning in 2 planes. Phased antenna array characteristics, accepted as reference: wide scan angle in the H-plane  not less than ± 450; a wide range of frequencies  at least 40%; small overall dimensions of the radiating aperture, not allowing to consider the canvas without taking into account edge effects; high energy potential, which means high electric strength (up to 1 kW per channel); reduced spurious emission outside the scanning area (more than 45 °). Here are the requirements for the emitters of the above-described active phased antenna array: Emitters dimensions must comply with the structural requirements for the antenna array construction (array step, emitters arrangement method) and not «obscure» each other in the area of the working scanning angles in the E and H plane. Emitters spatial bottom width in the grating should not be less than the angular width of the area of electronic scanning of the active phased antenna array beam. Beam main lobe distortion in the scanning area by an amount higher than 1 dB is not allowed. The emitter in the grating should be consistent with the power system in the working range of scanning angles and frequencies. Reduced spurious emission in directions outside the scanning area. High efficiency, to ensure both reception and transmission, and sufficient dielectric strength with limited dimensions. As active phased antenna array emitters, the simplest weakly directional antennas are used, which is associated with their low cost and high manufacturability. Technical solutions in the class of vibrator antennas (dipoles) are subjected to further analysis. The use of dipole antenna arrays in wide-angle and broadband applications leads to a number of technical limitations, such as: limited broadband emitters (including and as part of the antenna array), determined by their design features and mutual influence; a limited sector of the formation of unidirectional radiation (shape stability (radiation pattern) in the frequency band, determined by the condition for the appearance of interference lobes and the mutual influence of the emitters, leading to distortion of the amplitude-phase distribution; the occurrence of the effect of «blinding» of the lattice in individual sectors of the scan and frequencies associated with the effects of external (spatial) and internal interaction of emitters. Based on the above requirements for emitters, taking into account the design features of the AFAR, the following most important technical problems can be identified, the solution of which must be considered: ensuring a wide working frequency band; ensuring consistency in a wide sector of scanning angles; ensuring a stable spatial pattern of the emitter in the grating. Consider the general constructive methods that can be used to solve the above problems. Group them according to the constituent structural elements of the vibrator: Shoulders shape of the vibrators. The main limitation of the classical symmetric vibrator emitter using is its small working frequency band (up to 10%). So the passband ( 2f ) of a symmetric half-wave vibrator can be estimated by the following expression [5, p. 187]: 4 73,1 2 f f0 ,  WВ where is WВ  the wave impedance of the vibrator. It is determined by the cross section, shape and length of the shoulders. Balancing device type. Using a coaxial line determines the presence of balancing devices to power the shoulders of the vibrators. In the decimeter range, various types of balancing devices are used, the basis of which are various loops (including the U-elbow), glasses, transformers and slots, as well as their combinations. 3. Reflector shape (including matching structural elements). In fixed sector vibrator headlamps, a solid conductive surface is usually used as a reflector. Its shape and location relative to the shoulders has a strong effect on the bottom of the emitter in the grating and the matching of the grating in wide scanning angles and in the frequency range. The factor taking into account the influence of a flat aperiodic reflector on the DN is estimated by the expression: Fра  sin(kdr cos ) , where is dr  the distance from the vibrator to the reflector.

Frequency selective antenna radome based on metal-dielectric gratings and perforated screens

This article is devoted to the analysis of numerical study results of printed frequency selective surfaces scattering characteristics. It has been shown that these frequency selective surfaces may be used as antenna radomes. Numerical results have been obtained by full-wave simulation of frequency-selective surfaces with dielectric covers. The numerical research results of the scattering characteristics of printed frequency selective surfaces as antenna radomes based on metal-dielectric gratings and thick perforated screens have been presented. A comprehensive numerical study of microwave frequency selective surfaces based on multi-element multilayer printed reflectarrays and thick perforated screens has been carried out. Constructive solutions for metal-dielectric structures in integral design, realizing the functions of frequency selective surfaces, have been found. These solutions are based on performed numerical studies. The problems of constructive implementation of multilayer planar spatially selective as frequency selective surfaces have been considered. These frequency selective surfaces are integrated into radiation systems of modern multi-element printed phased arrays. The problems connected with creation of such arrays have been also considered. The numerical simulation results for frequency selective surfaces based on metal gratings with dielectric covers have been obtained. These results can be used to select the most rational options for the topology of metal-dielectric gratings. Such solutions may be useful for design of multifunctional radomes in microwave antenna systems. Based on the obtained numerical data, the possibilities of using flat gratings as frequency selective surfaces in the composition of antenna radomes have been considered. The spatial frequency-selective structures proposed in this work are performed as multi-planar printed gratings. These gratings are designed to ensure electromagnetic compatibility of closely spaced radio electronic sets. These radio electronic sets operate in close frequency ranges. They contain antenna arrays. These arrays are placed under the antenna radomes.

Experimental study of a double-circuit optoelectronic generator of radio-frequency signals

An urgent issue is the development of radio frequency generators operating in the microwave range, with high frequency stability, wide tuning band, as well as small size and weight. Microwave signal generators are used as part of radio electronic devices and devices for telecommunication, radio navigation and metrological purposes; therefore, improving their main characteristics is an important goal for the further development of radio electronic devices. A technological feature of optoelectronic generators is the combined use of solid-state components of modern HF and UHF optoelectronics, fiber optics and traditional components of UHF/EHF technology. According to the principle of operation and construction scheme, the optoelectronic generator is similar to the classic radio-frequency self-oscillator with a delay line in the feedback circuit. A feature of its work is the multifrequency nature of the generated oscillations, for which the conditions for amplitude balance and phase balance are satisfied. In the case of an optoelectronic generator, a feedback ring with a resonant system and a delay element is made using a single-mode fiber of a certain length. The signal delay time in the feedback loop is a significant parameter of the optoelectronic generator, which affects the noise and spectral characteristics of the generator. With an increase in the length of the fiber-optic path, the delay time in the feedback loop increases, thereby reducing the level of frequency noise. However, with an increase in the length of the fiber-optic path, the distance between adjacent modes of the optoelectronic oscillator also decreases, increasing the requirements for the bandwidth of the band-pass filter. The solution to this problem was the use of a multi-circuit optoelectronic generator. The paper considers a model created by the authors for a two-circuit optoelectronic generator with fiber-optic paths 1000 m and 30 m long. The available element base did not allow to reduce the generator's weight and dimensions. On this model, the characteristics of the circuit elements have been experimentally studied. The spectral characteristics of the generator have been estimated theoretically, which are in good agreement with the results of practical research. Phase noise is an important parameter in generator evaluation. Oscillators used as reference and measuring oscillators must certainly have a high frequency stability of the generated signal. Oscillations in autogenerators arise due to the effect of intrinsic noise in the circuit elements, which is one of the reasons for the occurrence of noise in the spectrum of the generator output signal. Intrinsic noise includes thermal, shot and flicker noises in semiconductor elements of generators. The article calculates the power spectral density of the phase noise of a single-loop oscillator and a dual-loop oscillator, which confirmed the assumption about a compromise between the noise level and the requirement for the filter bandwidth in a single-loop optoelectronic oscillator. An important advantage of optoelectronic generators, in comparison with generators built according to classical circuitry, is the absence of a compromise between the frequency tuning band of the device generation and the level of frequency noise.

Technical aspects of creating radiotechnical systems of information and command interface to ensure the functioning of complexes with unmanned aerial vehicles

One of the key components of the complexes with unmanned aerial vehicles (CUAV), which significantly affects the safety and reliability of operation, is the radio link for transmitting command-telemetric and target information of direct radio visibility (radio engineering system of information and command interface) between unmanned aerial vehicles (UAV) and the ground control and information processing point (GCSP). Heavy-class unmanned aerial vehicles can have several target loads simultaneously – a multispectral optical-electronic system, a digital aerial photo system, a radar system, a radio monitoring system, etc. Due to the fact that the flow of information with the payloads to the input of the radio link during peak time moments can be quite large, severe requirements are imposed as to the equipment of primary processing of the target information aboard the UAV and it’s compression in the recording information, and the bandwidth of the radio link in terms of transmission target information on GCSP for subsequent analysis and processing by the operator of the complex. Technical articles are the justification of modern approaches to the development of radio systems of information and team mates in the functioning of complexes with unmanned aerial vehicles, modeling and analysis of directional properties of the antenna system on the basis of the active phased array antenna (APAA) to ensure that decisions adopted targets CUAV, calculation and modeling of the use of various signal-code structures in the information and command-telemetry channels of the CUAV in order to assess the achievable data transfer rates and the energy budget of radio lines. The main tasks of the article are consideration of the nomenclature of possible target tasks of complexes with UAV, proposals for the technical implementation of radio systems of information and team mates, analysis of the advantages of using APAA as part of an unmanned aerial vehicle and a ground control and information processing point in order to improve the efficiency of UAV complexes in the end, modeling of directional diagrams in the azimuth and angular planes for receiving and transmitting modules and receiving and transmitting panels from the APAA, calculation of the energy budget of information and command radio lines, plotting the dependences of the error probability on the signal-to-noise ratio for various combinations of signal modulations and noise-tolerant encoding for various models of communication channels (additive white Gaussian noise – AWGN and binary-symmetric channel – BSC). The main results of the article include specific practical suggestions and recommendations on hardware and software approaches to the creation of antenna systems based on APAA as part of the CUAV, the effect of using modern approaches (reliability, reduced labor intensity and cost, improved performance characteristics), calculated signal-to-noise ratios for various methods of modulation and encoding, obtained as a result of calculations and mathematical modeling, as well as suggestions and recommendations for the rational use of specific types of signals and codes in the command-telemetry and information channels.

Signal «crosstalk» effect in the structure of the polarization attenuator channels

An ideal model of a polarization attenuator implies the full absorption of the tangential component of the electric field both in the resistive layer of rotor plates and those of stator plates. In a real attenuator, however, due to the incomplete absorption in the resistive layer of plates the so called “crosstalk” occurs. In most cases the “crosstalk” results in diminished attenuation values of a polarization attenuator. Furthermore, with the high frequencies and especially when the attenuation is high, it significantly affects the attenuation error of a polarization attenuator. This paper analyzes the effect of a series of geometric and electric parameters of the structure of a polarization attenuator’s channels on the “crosstalk” value. As distinct from the well-known calculation methods based on the calculation of separate elements of a polarization attenuator, an algorithm of point-to-point calculation from input to output ports of the entire device is offered. From the general principles of classical electrodynamics, in order to calculate the attenuation of electromagnetic wave in the longitudinal direction of the channel of the attenuator’s conduction system, a formula derived from the method of perturbation theory has been applied. This was possible thanks to an assumption about the weak perturbation of a conducted electromagnetic wave. This condition proves true in the said system thanks to choosing certain correlations between longitudinal and transverse dimensions of the polarization attenuator’s structural channels when the length of a plate with a resistive film is several times greater than the expanding electromagnetic wave as well as to choosing certain upper range values of a film’s surface resistance. From the general correlation of the perturbation theory method a precise expression aimed at defining the attenuation value in a polarization attenuator which is regarded as a result of functioning of geometric and electric parameters with consideration of frequencydependence of attenuation, is obtained. For numerical calculations an algorithm of reprojecting the electric field onto two orthogonal components with respect to a plate from the resistive film followed by defining with the help of the superposition principle the resulting field has been used. This procedure has been fulfilled with respect to each single unit every time the structure in the cross section of the polarization attenuator’s channels appeared heterogeneous. The authors performed the numerical calculations of characteristics of a polarization attenuator with operating frequency range from 53.57 to 78.33 GHz. A diagonally structured graph reflecting the changes of “crosstalk” in function of surface resistance of the film Rп in the range from 300 Оhm/m2 to 700 Оhm/m2 is offered. It graphically explains the physical process of transition from linear region of attenuation to saturation region. Recommendations on choosing Rп are provided. The authors demonstrate how with the use of the widely known in the literature results and the data on calculations provided in this paper one can evaluate the effect, which the heterogeneity of the plate with a film, in the form of out-of-flatness “fractures”, in particular, may have on the “crosstalk”. The numerical evaluations of the effect a diameter of the polarization attenuator channel has on the “crosstalk” are provided in the paper with the help of a double graph illustrating the “crosstalk” value being “expanded” on the attenuation deviations scale. The numerical calculation of the effect of a distortion of the plate with films in input/output ports of the polarization attenuator has been carried out. The paper proves the possibility of linearizing the characteristics and reducing the attenuation errors both by separate regulation of distortion wall in input/output ports and their common interaction. The physical interpretation of the calculation results of the polarization attenuator is provided. It describes the general principles and can be applied to any other operating frequency range of the polarization attenuator.