Spectral Characteristics Of Signal Research Articles

Mathematical modeling of microwave channels of a semi-active radar homing head

Objectives. Radar homing heads of guided missiles form a large group of radars which differ from other radars due to their specific purpose. The advantages of a semi-active radar homing head (SARH) include the ability to have a powerful irradiator at the command post and, as a result, a powerful reflected signal from the target. This results in an increase in the range of its detection and guidance. The absence of an emitter simplifies the missile’s onboard control equipment, reduces its weight and dimensions, thereby improving its maneuverability and increasing the guidance accuracy, resulting in the greatest distribution of this type of SARH. However, in order to determine the exact Doppler shift of the target signal as part of SARH, a reference signal with a frequency coinciding with the illumination transmitter signal must be supplied to the receiving path. This study aims to synthesize and analyze the SARH receiver circuit with improved accuracy characteristics.Methods. The following methods are used: statistical radio engineering; optimal signal reception theories; and computer modeling in CAD AWR Design Environment.Results. A mathematical model of the SARH receiver was obtained and analyzed. The proposed receiver model allows the spectral characteristics of signals to be calculated at any point of the microwave paths, as well as signal characteristics at the input of the head channel, at the output of the first conversion mixer, at the output of the first intermediate frequency selector, and at the output of the receiving path. The calculated values of the main characteristics of high-frequency channels are also given.Conclusions. The resulting model allows the frequency dependencies of main parameters of the receiving path, such as the gain factor, noise factor, decibel compression points, and third-order intermodulation intercept points to be estimated. The values obtained during the simulation are maximally close to existing systems, since the models of real-life and mass-used microcircuits thu created are used as the main elements when designing high- frequency paths. The model can be used to study methods of improving technical indicators, as well as to develop new principles and schemes for developing radioelectronic complexes, for example, when designing a receiving path using advanced radio photonics.

Divided spectro-temporal transformer for sound event localization and detection in real scenes

Sound event localization and detection (SELD) involves the detection of sound events (SED) and the estimation of their direction of arrival (DoA) by utilizing multichannel sound signals. Recent research in SELD has predominantly focused on deep neural network (DNN) based models, which specifically emphasize learning temporal context. Examples of these models include the convolutional recurrent neural network (CRNN) and the ResNet-conformer architecture, which handle spectral and channel information only as the embeddings of temporal features. To fully exploit spectral information providing a crucial cue for both SED and DoA, it is imperative to devise a network architecture that effectively learns both spectral and temporal contexts. In this regard, we propose a divided transformer architecture that separately identifies the spectral and temporal context to encourage the model to learn more spectral characteristics of signals while retaining the temporal context. The efficacy of the divided spectro-temporal transformer approach is validated using the DCASE 2022 and 2023 challenge task 3 datasets. Furthermore, a series of parameter studies carried out to optimize the performance of SELD demonstrates that the number of frequency bins for attention and the pooling location impact the performance, and the divided spectro-temporal transformer is beneficial for both SED and DoA.

THE METHOD OF IDENTIFYING THE TYPE OF UNMANNED OF THE AVIATION COMPLEX BY ITS RADIO SIGNALS

The article proposes a method for determining the type of unmanned aerial complex (UAC) based on its radio signals, which is based on a comparison of the estimated parameters of the UAV radio signals with known values stored in the database. The following characteristics and parameters of the signal are proposed as recognition features: the appearance of the amplitude-frequency spectrum (AFS) and spectrogram of the radio signal; radio line frequency range; accumulated ASF width; ASF width of the frequency element; spread spectrum parameters (hop duration; rate of frequency hopping spectrum spreading (FHSS); number of FHSS frequencies; FHSS frequency grid step); modulation parameters (symbol rate; modulation index); the position of the autocorrelation function (ACF) peaks; constant symbol sequences. Peculiarities of definition and application of the indicated recognition features are analyzed. It is shown that the most informative features are modulation parameters and constant symbol sequences. In order to increase the probability of correct recognition of UAC, in addition to the indicated features, it is suggested to use the power of received radio signals and the direction of the radio emission sources. A combination of two well-known approaches was used to make a decision about the type of UAC: the decision tree method and the minimum metric method. The application of the first made it possible to reduce the computational complexity due to the exclusion of operations for radio signals parameters evaluating that do not correspond to the decisions made at the previous stages. The minimum metric method was chosen taking into account the simplicity of its implementation and ensuring the possibility of expanding the list of known UAC radio signals without significantly changing the developed recognition method. The proposed method consists of six stages, in which recognition features corresponding to the signal spectral characteristics, spread spectrum parameters, modulation parameters, constant symbol sequences, power of the received radio signal and bearing on the UAV are determined in turn. The indicated features are compared with the known ones stored in the UAC radio signal database using the minimum metric method. In case of coincidence of the estimated and known information, a decision is made about the type of UAC, and the remaining stages are not performed. Verification of the developed method was carried out by applying it to the analysis of radio signals of known UAC, in particular, “Orlan-10”, “Supercam S350”, “Lancet”, “Eleron-3SV”.

The Influence of Parameters of Sensors and Receiving–Transmitting Devices with Dielectric Shells on the Spectral Characteristics of Signals Induced by an Artificial Thunderstorm Cell

The Influence of Parameters of Sensors and Receiving–Transmitting Devices with Dielectric Shells on the Spectral Characteristics of Signals Induced by an Artificial Thunderstorm Cell

Spectral Characteristics of Signals Induced on the Elements of Systems for Monitoring Power Facilities by Discharges from an Artificial Lightning Cell

Spectral Characteristics of Signals Induced on the Elements of Systems for Monitoring Power Facilities by Discharges from an Artificial Lightning Cell

SIGNAL FORMATION AND PROCESSING FEATURES FROM AUTODYNE RADAR WITH A WIDE FREQUENCY MODULATION BAND. (РART 1)

Subject and Purpose. In Part 1 of the paper, a mathematical model of an autodyne self-oscillator with frequency tuning by varactor capacitance varying is built and thoroughly analyzed for the features of signal formation in autodyne radar with a wide frequency-modulation bandwidth and a nonlinearity in the modulation characteristic. The aim of the study is to appreciate the action that the nonlinearity of the oscillator modulation characteristic exerts on the spectral characteristics of signals from frequency-modulation autodyne radar. Methods and Methodology. The research method is a mathematical analysis of the operation of an autodyne oscillator with electronic frequency tuning. To examine formation processes of emitted autodyne signals, the spectral, frequency and amplitude characteristics of signals from frequency-modulation autodyne radar are constructed with the use of numerical modeling techniques. Results. Numerical modeling of autodyne response signal spectra has been performed for various distances to the reflecting object and different modulating voltages across the varactor. It has been shown that a nonlinear dependence of the generator frequency on the varactor voltage makes for the broadening of the autodyne response signal spectrum. It has been found that as the object distance increases, the frequency of the autodyne response signal moves towards the higher frequencies, while the nonlinearity makes the spectrum broaden. The obtained calculation results refer to an 8-mm Gunn diode autodyne. Conclusion. The performed research of the spectral characteristics and into the features of signal formation in autodyne transceiver devices with a wide frequency tuning has shown that in order to achieve high resolution figures from autodyne radar, certain methods are needed to be developed for adjusting the laws of frequency modulation and for the processing of response signals from reflecting objects. Such a method and ways to solve these problems will be presented in Part 2 of the work.

A REMOTE SENSING SATELLITE LIGHTING DETECTION SYSTEM WITH HIGH DETECTION RATE AND LOW COMPLEXITY

Abstract. A payload was designed and implemented to do real-time and continuous lightning detection which can be used on remote sensing satellite. The payload consists of sensor unit and electronics unit. Based on the analysis of lighting signal spectral characteristics, the sensor unit adopts ultra-narrowband filtering technology to realize lightning signal spectral filtering, and uses high frame rate area array CMOS device as photosensitive element to obtain image information. In order to reduce the complexity and hardware resources of the electronics unit, a continuous mean elimination method is used to detect lightning signals according to the instantaneous characteristics of lightning. The self-adaptive double threshold recognition method is utilized to detect the recognized lightning signal, which significantly reduces the detection time with a detection rate up to 95%. The electronics unit has the function of quick adjustment of detection threshold through instruction, which provides a more flexible application space for lightning characteristics analysis on the ground. In addition, the system can be used to detect other point or surface target by the change of optical design according to the different characteristics of the detection target, such as the large-scale fire disaster or military target.

Spectral Characteristics of Signals Induced by an Artificial Thunderstorm Cell on Dummy Elements of OHPL Monitoring Systems Protected by Dielectric Shells

Spectral Characteristics of Signals Induced by an Artificial Thunderstorm Cell on Dummy Elements of OHPL Monitoring Systems Protected by Dielectric Shells

Spectral characteristics of signals induced on elements of monitoring systems of energy facilities by discharges from an artificial lightning cell

Spectral characteristics of signals induced on elements of monitoring systems of energy facilities by discharges from an artificial lightning cell

Influence of parameters of sensors and receiving and transmitting devices with dielectric shells on the spectral characteristics of signals induced by an artificial lightning cell

Influence of parameters of sensors and receiving and transmitting devices with dielectric shells on the spectral characteristics of signals induced by an artificial lightning cell

Spectralcharacteristics of signals induced by an artificial lighting salon model elements of overhead line monitoring systems protected by dielectric shells

Spectralcharacteristics of signals induced by an artificial lighting salon model elements of overhead line monitoring systems protected by dielectric shells

Peculiarities of spectrum of electromagnetic signals induced by discharges from artificial thunderstorm cell

Results of an investigation of the peculiarities of a spectrum of the electromagnetic signals induced nearby discharges between an artificial thunderstorm cell and a ground have presented. It was experimentally found that the impulse current parameters and an intensity, form, spectral characteristics of the induced electromagnetic signals depend on a variant of a discharge formation from an artificial thunderstorm cell (upward discharge, downward discharge, or counterpart discharge). Significant difference of the wavelet spectrum characteristics of the electromagnetic signals registered by the antennas in the vicinity of discharge formation has been found for these three variants. Significant difference of the spectral characteristics of the electromagnetic signals induced on nearby antennas during the time of the first and subsequent current impulses of a discharge between an artificial thundercloud and a ground: in average, subsequent discharges have more less characteristic frequencies. Possible reasons of that differences have discussed in paper. Role of the powerful streamer discharges during the main stage formation in the appearance of the ultrahigh frequency range of the induced electromagnetic signals has considered. Some dependencies between the spectral characteristics of signals registered by antennas and the parameters of the current impulses for the different variants of the main stage of the discharge between the artificial thunderstorm cell and the ground have been established. The possibility of applying the results obtained for improving the operation of lightning direction finding systems is being considered.

Detection of cracks in green products of powder metallurgy by means of laser vibrometry

Cracking of green parts in powder metallurgy (PM) is a big concern in PM industry. Detection of cracks in green parts before sintering can prevent recycling of already sintered parts or production of defective ones. As opposed to sintered parts, where the presence of cracks is well revealed by impact spectroscopy, it is challenging for green parts. The reason is an extremely low mechanical quality factor of these parts composed of compacted but non-sintered metal powder particles. Low mechanical integrity of particles causes the absence of pronounced resonances of the parts. The aim of the study was to test a possibility to discerning healthy and cracked green parts using spectral characteristics of signals obtained by laser vibromery. Four similar green PM gear wheels made of steel powder were obtained from a PM manufacturing company, two of them were healthy and two with simulated cracks that appeared in the area of stress concentration between the hub and the disc. The experimental setup included a Polytec PSV-500 scanning laser vibrometer and a Bruel&Kjer vibration stand type 4824. Integrated spectrograms in the frequency range 50 – 3500 Hz were recorded upon a 95-point network on the gear surface at different vibration intensities proportionally graded in the range from 1 to 5. Comparison of the 3D (frequency-intensity-amplitude) vibration spectrograms showed that the defected specimens with cracks differed from the healthy ones in the following features: resonance frequency shift and/or splitting of resonances when the load changes. The study confirmed the principal possibility of cracks detection in green PM parts using laser vibrometry regardless the crack location in the part. The aim of further studies is to determine the sensitivity limit in terms of crack size.

A 90 GHz SINIS Detector With 2 GHz Readout

A superconductor-insulator-normal metal-insulator-superconductor (SINIS) detector integrated in a planar 90 GHz band twin-slot antenna with a 2 GHz superconducting resonator readout was fabricated and experimentally studied. In order to achieve high pixel count, the traditional dc readout of the SINIS detector is replaced by NbN coplanar 13.850 mm long superconducting resonator. SINIS detectors have traditionally dc Junction Field Effect Transistor (JFET) room-temperature readout. Such readout requires individual wiring for each pixel, while the microwave readout is far less cluttered as only one coaxial line is needed for hundreds of devices. Such readout operates similar to frequency domain multiplexing (FDM) for microwave kinetic inductance detectors (MKID). The planar twin slot antenna has two parallel slots in a metal ground plane which are excited coherently by short sections of a coplanar waveguide (CPW) line with a SINIS detector at the center. One section of the CPW is extended past the slot in a long superconducting section which functions as a quarter wavelength resonator. This resonator is short circuited to the ground plane at the far end, with the expected open circuited end terminated by the SINIS detector in the antenna. We measured the response of sample to black body radiation temperatures 6 K and 9 K. The corresponding dynamic resistance maximum drops from 50 kΩ down to 30 kΩ. An RF readout channel comprising a coplanar coupler and a coplanar resonator has a resonant frequency of 1.8 GHz. Unloaded Q factor (without incoming irradiation) is 200. The signal spectral characteristics and the response to the black body radiation have shown design values as expected.

DVB-T-Based Passive Forward Scatter Radar: Inherent Limitations and Enabling Solutions

This article investigates the target detection capability of a passive forward scatter radar (PFSR) exploiting a digital video broadcasting - terrestrial (DVB-T) transmitter as illuminator of opportunity. By means of theoretical and simulated analyses, it is shown that conventional processing schemes might suffer from significant performance degradation when exploiting orthogonal frequency division multiplexing (OFDM) waveforms of opportunity compared to other broadcast transmissions (e.g., frequency modulation radio broadcast). Specifically, the direct application of conventional processing approaches to the case of a DVB-T PFSR is demonstrated to yield: 1) a nonnegligible increase of the competing background level and 2) a steeper fading of the target response due to the intrinsic characteristics of the exploited waveforms of opportunity, above all the modulation scheme and the signal spectral characteristics. Therefore, appropriate signal processing techniques are proposed to avoid these effects which jeopardize the target detection capability. The conceived processing scheme exploits the digital nature of the employed waveforms and a subband approach for improving both the interference cancellation stage and the target signature extraction. The benefits of the proposed approach are illustrated by means of theoretical and simulated analyses. The application of the resulting processing scheme against experimental data proves its effectiveness in practical scenarios.

Experimental and Theoretical Investigation of an Oscillator with Collisions

The oscillations of a nonlinear electromechanical oscillator with elastic collisions have been studied. A theoretical model has been built around the equation of motion including an elastic force that is calculated in terms of the Hertz contact theory. It has been shown that an oscillator with collisions may exhibit bifurcations and stable-focus and limit-cycle attractors. Fourier filtration has been applied to analyze the spectral characteristics of signals.

Denoising Algorithm for the FY-4A GIIRS Based on Principal Component Analysis

The Geostationary Interferometric Infrared Sounder (GIIRS) is the first high-spectral resolution advanced infrared (IR) sounder onboard the new-generation Chinese geostationary meteorological satellite FengYun-4A (FY-4A). The GIIRS has 1650 channels, and its spectrum ranges from 700 to 2250 cm−1 with an unapodized spectral resolution of 0.625 cm−1. It represents a significant breakthrough for measurements with high temporal, spatial and spectral resolutions worldwide. Many GIIRS channels have quite similar spectral signal characteristics that are highly correlated with each other in content and have a high degree of information redundancy. Therefore, this paper applies a principal component analysis (PCA)-based denoising algorithm (PDA) to study simulation data with different noise levels and observation data to reduce noise. The results show that the channel reconstruction using inter-channel spatial dependency and spectral similarity can reduce the noise in the observation brightness temperature (BT). A comparison of the BT observed by the GIIRS (O) with the BT simulated by the radiative transfer model (B) shows that a deviation occurs in the observation channel depending on the observation array. The results show that the array features of the reconstructed observation BT (rrO) depending on the observation array are weakened and the effect of the array position on the observations in the sub-center of the field of regard (FOR) are partially eliminated after the PDA procedure is applied. The high observation and simulation differences (O-B) in the sub-center of the FOR array notably reduced after the PDA procedure is implemented. The improvement of the high O-B is more distinct, and the low O-B becomes smoother. In each scan line, the standard deviation of the reconstructed background departures (rrO-B) is lower than that of the background departures (O-B). The observation error calculated by posterior estimation based on variational assimilation also verifies the efficiency of the PDA. The typhoon experiment also shows that among the 29 selected assimilation channels, the observation error of 65% of the channels was reduced as calculated by the triangle method.

Analysis of confidentiality of information transfer in DSSS systems in conditions of limited systems of used signal constructions

Information security in telecommunications can be provided at the physical level of telecommunication systems by means of energy and structural secrecy of information transfer. Spread-spectrum telecommunications, in particular the DSSS (Direct Sequence Spread Spectrum) technique, are the most suitable for the implementation of such approach to information security. Ensuring the necessary level of structural secrecy of information transfer using DSSS technique is that this technique uses systems of signal constructions with a sufficiently large number of signals in the system. There are requirements to correlation properties of each such signal construction, because in accordance with the Wiener-Khinchin theorem they determine the spectral characteristics of signals in a telecommunication system and, as a result, the structural spectral and energy secrecy of information transfer. The problem boils down to the fact that the systematic deterministic methods for synthesizing systems of signal constructions with a low peak sidelobe level of the autocorrelation function for the case of an arbitrary length of signal constructions and the number of ones in the system of signals are unknown, and the complexity of this problem is associated with an algorithmic undecidability of arbitrary algebraic Diophantine equations. The confidentiality of information transfer at the physical level of DSSS telecommunication systems while using some known systems of signal constructions with a low peak sidelobe level of the autocorrelation function and in the case of attacks, which are performed by an unauthorized user by means of optimal signal processing methods (optimal detection of biorthogonal signals), is analyzed in the article.

Wavelength multiplexing of four-wave mixing based fiber temperature sensor with oil-filled photonic crystal fiber.

A fiber temperature sensor based on four-wave mixing (FWM) with an oil-filled photonic crystal fiber (PCF) is proposed in this study, and a multipoint measurement based on the wavelength multiplexing of such sensors is constructed for the first time. The sensing performance and signal spectral characteristics of the temperature sensor are theoretically and experimentally studied. The maximum temperature sensitivity of the signal light of 0.207 nm/°C is achieved using a FWM sensing fiber with a length of 10 cm. The signal wavelength response to excitation power is also explored in this experiment. Results showed that the temperature sensor is relatively insensitive to the fluctuation of power change. The wavelength multiplexing of a FWM-based PCF temperature sensor also presents the possibility of multiplexing measurement and multipoint sensing, and high multiplexed capability is theoretically predicted to be obtainable with optimized sensitivity and splicing loss.

Vibration and acoustic emission monitoring the stability of peakless tool turning: Experiment and modeling

Acoustic emission (AE) study of steady and chatter mode peakless tool turning has been carried out in order to reveal an acoustic emission response to the workpiece chatter during fine turning. Molecular dynamics simulation of acoustic emission response to chatter was used to find out fundamental system characteristics. Experimental dependencies of AE signal amplitude, median frequency and power spectrum have been obtained and compared to those obtained from the molecular dynamics (MD) simulation. Both experimental and MD simulated AE signal spectral characteristics proved to be sensitive to chatter mode vibrations. Median frequency showed a drop in chatter mode cutting as well as power spectrum shifted to the low frequency range. Such a relationship has been attributed to the growing level of the system potential energy.