The features of the use of radio waves with linear and circular polarization at incoherent scatter (IS) radars of the very high frequency (VHF) band are considered. We give examples of calculating the altitude distribution of the ionospheric electron density from the results of measurements calibrated with the ionosonde data when using the circularly polarized sounding signal, as well as from the IS signal power minima and maxima associated with the Faraday rotation when using a linearly polarized signal. The disadvantages of these methods are noted. In the first case, the ionosonde data are bound to the obtained by IS technique normalized altitude profile of the electron density only at one altitude point; at certain events in the ionosphere, the ionosonde data may be unreliable or even absent (for example, in the presence of the sporadic $\mathbf{E}_{s}$ layer). In the second case (the mode of analyzing the wavelike altitude profile of the IS signal power), there are errors in determining the centers of the nodal points, especially when signal-to-noise ratio is low. We proposed a version of calculating the absolute values of the electron density using an altitude profile that is the result of multiplying the voltages of two circularly polarized components of the linearly polarized IS signal with opposite directions of the electric field vector rotation, when the linearly polarized sounding signal is used. In this case, a wave-like alternating function associated with the Faraday Effect is obtained with the help of special calculations. This function is used to determine the intervals between its adjacent zero values, and the resulting height intervals are uniquely related to the average electron density for each of them. Due to the high accuracy of determining the points of intersection of the function with the abscissa axis, the accuracy of electron density measurements using the Faraday Effect increases significantly, especially in the presence of noise. We proposed a structure of upgraded hardware for implementation of such mode of additional processing of the IS signal orthogonal components. Using computer simulation, an example of the separate reception of circularly polarized components of the IS signal with their multiplication is given, including a situation when noise-like components are present.
This paper extends the work of the authors on highly sensitive broadband silicon germanium heterojunction bipolar transistor (SiGe HBT) low-noise amplifiers with regard to their optimization based on the genetic algorithm and proposes a design methodology. The methodology aims at achieving a sub-1 dB noise figure at room temperature. The amplifier uses inductively degenerated common-emitter transistors in a cascode configuration, and a noise figure close to the minimum achievable one is obtained by biasing the SiGe HBTs at an emitter current density corresponding to minimum noise. Noise matching is achieved by connecting several identical transistors in parallel, while impedance matching relies on limiting the number of passive components for the matching network to the absolute minimum. This is done by the base-collector capacitance used as a network element and by means of an additional noiseless on-chip component. A sub-1 dB noise figure of 0.6 dB is shown by simulation without optimization by the genetic algorithm, with a return loss better than 10 dB, using a 130 nm SiGe HBT process. The bandwidth of the low-noise amplifier spans from 300 MHz to 1.4 GHz. The methodology validates that SiGe HBTs are suitable for broadband ultra-low noise amplifiers for radio astronomy and that the performance of the proposed amplifier can be further optimized.
Despite the advances in cancer nanotheranostics, there are limitations associated with targeted delivery to the tumor and objective image interpretation. This paper investigates the role of a magnetic nanocomplex (MNC) synthesized from gadopentetic acid and antitumor agent doxorubicin (DOX) as a theranostic system to improve antitumor activity under constant magnetic (CMFs) and electromagnetic fields (EMFs) as well as provide additional prognostic information on magnetic resonance imaging (MRI) scans in animals with Lewis lung carcinoma. Heterogeneity values in the tumor core were twice higher than those in the tumor periphery or the peritumoral tissue on both T1-weighted and short tau inversion recovery (STIR) images. Heterogeneity parameters extracted from the tumor core and periphery as well as the fractal dimension of the peritumoral tissue were significantly different between conventional DOX and MNC + CMF + EMF treatment $\boldsymbol{(\mathrm{p}\leq 0.05)}$ on STIR images. Tumor growth kinetics correlated negatively $\boldsymbol{(\mathrm{r}_{\mathrm{s}}=-0.89)}$ with the fractal dimension of the peritumoral tissue on MRI scans after DOX, while a strong positive correlation $\boldsymbol{(\mathrm{r}_{\mathrm{s}}=0.83)}$ was noted in animals receiving MNC + CMF + EMF $\boldsymbol{(\mathrm{p}\leq 0.05)}$ . Treatment response evaluation based on multifunctional MNCs can deepen our understanding of physicochemical interactions between the tumor and its microenvironment and drive personalized approaches for cancer nanotheranostics.
The problem of finding the algorithm for estimating the spectral power density (SPD) of the input signal of the receiver when observing the signal from the output of the quadratic detector of the receiver is solved. Formulas for calculating the boundary errors in estimating the SPD parameter and the fluctuating sensitivity of a radiometric receiver operating according to the obtained algorithm are obtained. The possibility of using the likelihood functional for stationary Gaussian processes in solving the problem of signal processing after a quadratic detector is substantiated by simulation modelling.
New modification of the integral equation technique is used for mathematical modelling of the plane E- polarized electromagnetic wave scattering by a single flat electrically conductive strip and flat grating consisting of finite number of electrically conductive strips. The scattering problems are formulated in the form of two-dimensional external mixed boundary-value problems for the homogeneous Helmholtz equation on corresponding segment or system of segments. The target of the examination is to find correct, simple and effective mathematical model of the plane E- polarized electromagnetic wave scattering by electrically conductive strip gratings.
The problem of the plane (electromagnetic or acoustic) wave scattering by a multi level not classical coplanar system of flat impedance strips is analyzed on the base of the singular integral equation method. Considerable attention is focussed on some types of terrible “Devil stairs” functions, corresponding to some self similar fractals with a variable fractal dimension. It is important to have a lot of not classical sets for usage in construction of the coplanar system of impedance strips. The stages of the “Devil stairs” function constructive procedure can be useful for modelling of natural specific irregular zones in regular two-dimensional space. A partial (but important for applications) case of sparsely filled coplanar strip system is analyzed. In this case, the plane wave scattering problems have explicit asymptotical solutions in the closed analytical form.
The authors take into consideration the placement of the antenna sheet and the transmit/receive modules of the active phased array antenna in its operating position to propose a new efficient design of the air-cooling system for transmit/receive modules with built-in heat pipes of simplified design. This paper presents the results of computer simulation of two alternative designs of the air-cooling system based on a heat sink: a version without heat pipes and one with 16 flat heat pipes with threaded capillary structure. The effect of changing the velocity of cooling air flowing in the heat pipe channels from 2 to 10 m/s on the temperature field distribution and the temperature of the hottest transistors is demonstrated for both versions at a total thermal power of 8 transistors amounting to 224 W. At an air velocity of 2 m/s, the use of heat pipes in the cooling system made it possible to reduce the temperature of the hottest transistor by 20 K, and at an air velocity of 10 m/s, by 14.9 K. The recommended air velocity in the heat sink channels was determined to be in the range from 4 to 8 m/s, in which the temperature of the transistors is reduced to 33.3% compared to the heat sink design without heat pipes.
The paper deals with improving characteristics of airborne magnetometer in an algorithmic way due to proper initial alignment of the device. The possibility of ensuring maximum accuracy of determining the value and direction of the vector of the terrestrial magnetic field, and improving the sensitivity of the magnetometer for determining local fluctuations of the terrestrial magnetic field is considered. Appropriate calculations and graphical dependencies are represented.
RSSI is typically used for the input power estimation in wireless sensor networks. It is necessary to consider the nonlinearity of the receiver amplitude response, which depends on the RSSI circuitry, and the effects of multipath propagation, which are inevitably present in the open space measurements of the actual input power. The paper proposes a method for calculating the input power of a LoRa receiver by adding a certain offset coefficient to the RSSI values. This coefficient was obtained experimentally for LoRa platforms with a signal frequency of 433 MHz, 868 MHz and 2.4 GHz and various spreading factor values. The proposed technique makes it possible to estimate propagation path losses with an accuracy sufficient for estimated calculations. The loss estimation error does not exceed 10–12 dB depending on the distance.
The method, methodology and algorithm for modeling one of the components of the satellite navigation signal monitoring system on the territory, dilution of precision, is given. The earth's surface is approximated by a grid whose nodes are given by latitude and longitude. At each point, dilution of precision is evaluated at the current time and presented as arrays of data and graphic images. The initial data for modeling and research is the almanac of GPS, GLONASS, GALILEO, BEIDOU, pseudoranges to navigation satellites. Dilution of precision is determined from the diagonal elements of the covariance matrix used to obtain the navigation solution. Dilution of precision can be obtained at a given time for any of the satellite systems or their combinations. There are graphical representation of some of the main results of the study.
The mathematical model of the influence of non-Gaussian interference has been developed and a nonlinear method of non-Gaussian interference in signal acquisition and information processing by measuring means based on asymptotically optimal reception has been developed. According to the criterion of maximum likelihood in the asymptotic approximation, it was found that the main node of the receiver of the decision device, which provides the maximum, but possible attenuation of strong non-Gaussian interference, is a nonlinear inertial converter, the amplitude characteristic of which is uniquely determined by interference. Analysis of the characteristics showed a strong suppression of interference with the optimal characteristics of the block of non-Gaussian interference and quite large - when using a limiter with a positive excess of the distribution.
Millimeter-wave interferometer has been developed and preliminarily studied for the stand with a plasma gun. The high-density plasma can exist in the developed plasma stand using arc discharge at the vacuum chamber. Such techniques are used for plasma processing in the manufacturing and material sciences. Quasioptical antennas as well as sealing and structural elements for their installation inside plasma gun ports have been developed. The tests of the developed interferometer and antennas were performed.
In the presented work, the relative throughput of both a ground-based range transponder and the entire short-range radio engineering system is estimated under the action in the range channel of the total flow of range request signals. And also considered the requesting signals for unauthorized use of the rangefinder channel transponder by the interested party under the action of chaotic impulse noise flow. The evaluation was carried out on the basis of the representation of the channel for measuring the range of short-range radio engineering systems in the form of a non-synchronous network. We assume that the range request signals are serviced by an open single-channel queuing system with refusing according to the service scheme of the first correctly received range request signal.
The article shows the possibility of reducing the temperature coefficient for the reference voltage source (RVS), built on bipolar transistors. In the first step is offered the structural scheme with compensators of decrease in temperature characteristics. The second step is to generate additional voltage to compensate for the nonlinearity of the temperature characteristic. The next step is to develop a circuit of an electrical type compensator and an example of including one and two compensators in an uncompensated circuit. It also determines the rule for the use of subsequent compensators, if necessary. The parametric optimization of the offered examples of RVS is carried out. An experimental study of the example of RVS with one link of compensation was also conducted. As a result of optimization, the value of temperature instability was reduced from 4.4 mV in the basic circuit to 1.2 mV for one compensator, and to 0.515 mV for the case of two compensators, which proves the effectiveness of the proposed strategy and models.
The features of the frequency impedance characteristic, as well as the transmission response of a resonator based on two open-circuited stubs, are considered. The advantage of such a resonator is the high steep slope of the frequency response and the presence of two zeros near the resonant frequency. A noticeable selectivity deterioration in the stop bands when detuning from the resonant frequency of a resonator limits its use. Solutions on the basis of transmission line sections, allowing to improve the suppression in the stop-bands and increase the quality factor of such resonator, are proposed and analyzed.
this paper describes and analyzes two-stage channel frequency response estimation methods for digital communication systems with OFDM technology based on pilots from current received symbol. Among them two-stage method for estimation of channel frequency response and two-stage method for joint estimation of informational symbols and channel frequency response. Above methods are based on Kalman filter. At the first stage performs processing in forward and backward direction in relation to the data array. At the second stage performs combining the results. The statistical properties of the channel are assumed to be known.
A topology concept of a residential power supply system utilizing renewable sources and a storage battery is proposed. The system is modular and consists of grid-tie inverter and several DC-DC converters interfacing renewable sources and/or storage batteries to a common DC link. An original control approach for the grid-tie inverter is proposed allowing it to serve as an active harmonic filter (without need to install additional current sensors, as in conventional active power filters). The system has an ability to serve as an uninterruptible power supply in case of grid failure, provided that renewable sources and storage battery power is sufficient to feed the loads. An optional “zero-export” function is also provided.
The study presents a method of taking into account the impact of wind speed changes on the payback period and the maximum number of batteries to balance energy in distributed generation systems with wind turbines. To account for the impact, the probabilities of minimum and maximum wind speeds depending on the probability distributions of wind speed are used. An array of wind speed data for 5.7 years was selected and described using three probability distributions, for which the Kolmogorov-Smirnov test for 2 data sets (wind speed data set and data set generated with given distribution parameters) with a significance level of 5% allows to assume that there is a statistical relationship between the samples. Missing wind speed data was reconstructed using the method of filling gaps with selection. The probabilities of occurrence of minimum and maximum wind speeds without and with reconstruction of gaps for the three probability distributions were compared. The payback period of the HZB12-180FA lead-acid battery and the maximum number of such batteries when using the VE-2 wind turbine and predefined operating modes of the system have been estimated.
Multifunctional radars allow tracking several air objects at the same time in the time division mode. Tracking mode of various air objects in the radar is provided by radio tracking systems in terms of range, radial velocity and angular coordinates, which, as a rule, use digital systems for processing and filtering spatial coordinates, the algorithms of which are synthesized on base of adopted model the air objects movement and model of observation. The paper proposes a method for selecting apriori uncertain characteristics of external influences, which are used in models of air objects movement and models of observations for synthesis of tracking algorithms with fixed parameters based on the criterion of minimum average losses in tracking accuracy. The results of solving problem choosing characteristics one of variants the model of maneuvering air objects movement for tracking algorithm in range are presented.
