Chirp Signal Research Articles

Application of probing signals with zero autocorrelation zone for suppression of recurrent range interference in synthetic aperture radars

The problem of overlap of echo signals of adjacent probing cycles in synthetic aperture radars (SARs), called range ambiguity interference, or recurrent interference, is considered, which is usually solved by using orthogonal linear frequency modulated (chirp) and phase-code shift keyed (PCSK) in adjacent SAR probing cycles, which allows you to successfully suppress false signals from bright point targets from adjacent repetition periods. For SAR, various types of probing PCSK signals with a zero autocorrelation zone are considered, which make it possible to successfully solve the problem of suppressing recurrent interference from both point targets and extended objects. A comparative analysis of the correlation characteristics of orthogonal chirp and PCSK signals with various types of PCSK signals with a zero autocorrelation zone has been carried out.

Control of a High-Speed Channel Spectrum Using an Off-Center Signal Chirp

Control of a High-Speed Channel Spectrum Using an Off-Center Signal Chirp

Research and Design of BPM Shortwave Time Signal Modulation Technology Based on Chirp

The shortwave time service system is a vital land-based wireless time service solution, serving as a supplement and backup to the global navigation satellite system. It ensures that time users can access reliable timings, especially in extreme situations. However, the current BPM shortwave time service signal in China faces issues such as insufficient anti-interference reception capabilities and poor timing accuracy. This paper capitalizes on the advantages of Chirp signals and explores a new modulation technology for BPM shortwave time signals that is compatible with the existing modulation system. A Dual Chirp Time-Division Combined Modulation (DCTDCM) scheme is proposed for broadcasting two time signals: Coordinated Universal Time (UTC) and Universal Time 1 (UT1). Furthermore, an in-depth study of the receiving method for this scheme is conducted, with detailed design of its parameters. The designed DCTDCM signals offer a spread spectrum gain of 24 dB and a multipath resolution capability of at least 125 μs, significantly enhancing the anti-interference reception and anti-multipath attenuation capabilities of shortwave time signals. As a result, the availability and timing accuracy of shortwave time signals are substantially improved. Finally, extensive comparative experiments on reception performance validate the effectiveness of this approach.

Review on application of fractional Fourier transform in LinearFrequencyModulation signal and communication system

Traditional Fourier transform often apply to analyze and process stationary signals, however, it is weak for time-varying non-stationary signals, and fractional Fourier transform (FRFT) can better solve such problems. The FRFT can be comprehended as the expressive methods on the fractional Fourier domain constituted by the spinning coordinate axis of the signal anticlockwise about the origin at arbitrarily Angle in the time-frequency plane. In this paper, the improved fractional Fourier transform is combined with other calculation methods to achieve high precision estimation of chirp signal parameters. And the communication system built on weighted fractional Fourier transform and discrete fractional Fourier transform is studied and simulated respectively, which verifies the feasibility and improves the anti-jamming and anti-interception ability of the communication system.

Prospect of Detecting Magnetic Fields from Strong-magnetized Binary Neutron Stars

Binary neutron star mergers are unique sources of gravitational waves in multi-messenger astronomy. The inspiral phase of binary neutron stars can emit gravitational waves as chirp signals. The present waveform models of gravitational waves only considered the gravitational interaction. In this paper, we derive the waveform of the gravitational wave signal taking into account the presence of magnetic fields. We found that the electromagnetic interaction and radiation can introduce different frequency-dependent power laws for both the amplitude and frequency of the gravitational wave. We show from the results of the Fisher information matrix that the third-generation observation may detect magnetic dipole moments if the magnetic field is ∼1017 G.

Enhanced SAR Compression through Multi-Look Doppler Compensation and Auto-Focusing Technique.

This paper presents a simple and streamlined compensation technique for improving the quality of synthetic aperture radar (SAR) images based on the Range Doppler Algorithm (RDA). Incorrect Doppler estimation in the space orbit, caused by unexpected radar motion errors, orbit mismatches, and other factors, can significantly degrade SAR image quality. These inaccuracies result in mismatches between the azimuth-matched filter and the received Doppler chirp signal. To address this issue, we propose a Doppler estimation method that leverages the Fractional Fourier Transform (FrFT) and cross-correlation techniques. The received signals are compared with the azimuth-matched filter based on the rotation angle in the FrFT domain, and the Doppler centroid is adjusted to achieve the optimal alignment. This process ensures high correlation values and enhanced resolution in the final SAR image. The efficacy of the proposed technique is validated through experiments using real spaceborne SAR data from the practical satellite. The results demonstrate significant improvements in image quality and resolution compared to conventional algorithms, highlighting the advantages of our approach for various remote sensing applications.

A High-Precision, Ultra-Short Baseline Positioning Method for Full Sea Depth

To fulfill the demand for high-precision underwater acoustic positioning at full sea depth, an ultra-short baseline (USBL) positioning method with the square array based on the least squares estimating signal parameters via rotational invariance techniques (LS-ESPRIT) algorithm is presented in this paper. A combination of beam tracking and beamforming is employed to improve the accuracy of direction-of-arrival (DOA) estimation and, consequently, enhance overall positioning accuracy. In order to mitigate the issue of position jumping resulting from phase ambiguity in traditional four-element cross arrays, we have improved the stability of the positioning algorithm by utilizing a multi-element square array and employing the LS-ESPRIT algorithm for DOA estimation. Furthermore, the signal detection method integrating the correlation coefficient and ascending/descending chirp signals is employed to enhance the reliability of the location algorithm. Simulation analysis and experimental results demonstrate that the proposed algorithm effectively enhances positioning accuracy and improves the problem of jumping in positioning results.

Design and implementation of 1GHz bandwidth SAW chirp transform spectrometer

Abstract Because of its low power consumption and high stability, the surface acoustic wave (SAW) chirp transform spectrometer (CTS) has been widely applied in deep space missions for exploring space beyond Earth. In this paper, a comprehensive description of a new CTS with 1GHz bandwidth and 100kHz spectral resolution is presented. This spectrometer is implemented in a combination of digital and analog. The Chirp signal with a bandwidth of 2 GHz is generated by DDS as the expander and a SAW chirp filter with 1GHz bandwidth and 10μs dispersion is used as the compressor. The system is completely constructed for the back-end data acquisition and processing part of the CTS. Aiming at the detection demand and acquisition problem of weak signals in deep space in the field of deep space exploration, the pulse integration technique is used to improve the detection capability of the Chirp transform spectrometer for weak signals, and the synchronization and real-time implementation of the high-speed system in the process of pulse integration are discussed and designed in detail. The pulse width of the accumulated spectrum is about 1.2ns, and the corresponding frequency resolution is 120kHz, which is close to the theoretical value.

Modelling Low-Frequency Vibration and Defect Detection in Homogeneous Plate-Like Solids

The inspection of thick-section sandwich structures with skins around core materials such as honeycomb, balsa, and foam relies on low-frequency vibration techniques to identify defects through changes in amplitude or phase response. However, current industrial methods are often limited to detecting specific types of defects, potentially overlooking others. Moreover, these methods do not gather detailed information about the defect type or depth, as they only analyse a small portion of the available data instead of the full relevant response spectrum. This paper explores the scientific basis of using low-frequency vibration in the pitch-catch variant for defect detection in homogeneous solids, through analysis of the full relevant frequency spectrum (5–50 kHz). Defects in structures lead to reduced local stiffness and mass in the affected area, causing resonance in the layer above, resulting in amplified vibrations known as local defect resonance (LDR). In this work, an aluminium plate with a 40 mm diameter circular flat-bottomed hole (FBH) at a depth of 1 mm (representing a skin defect) is excited with a chirp signal of 5–50 kHz, and the response is monitored 17 mm away from the excitation point. Finite-element analysis (FEA) is used for the numerical model, addressing challenges in creating an accurate model. The process to optimise the numerical model and the reduce model-experiment error is outlined, including challenges such as the lack of knowledge of material damping. The study emphasizes the importance of modelling the probe’s stiffness and damping effects for achieving agreement between the model and experiment. After incorporating these effects, the maximum LDR frequency error decreased from approximately 3 kHz to less than 1 kHz. In addition, this study presents a method with the potential for defect classification through comparison to modelled responses. The minimum difference error was used to quantify the resonance frequencies’ error between the model and the experiment. Since the resonant frequencies are a function of the defect’s shape, size, and depth, a relatively low root mean squared (RMS) error across the resonance frequency error spectrum indicates the defect’s characteristics. Finally, defect detection and sizing using the pitch-catch probe are explored with a wide-band excitation signal and a line scan through the mid-plane of the defect. A method for defect sizing using a pitch-catch probe is presented and experimentally validated. Accurate defect sizing is achieved with the pitch-catch probe when the defect width is at least ≥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ge $$\\end{document} twice the 17 mm pin-spacing of the probe.

Interrupted-Sampling Repeater Jamming Countermeasure Based on Intrapulse Frequency–Coded Joint Frequency Modulation Slope Agile Waveform

Interrupted-sampling repeater jamming (ISRJ) is widely used in the field of electronic countermeasures, and can severely affect radar detection. Therefore, the problem of ISRJ suppression is a compelling task. In this paper, we propose an ISRJ suppression method based on an intrapulse frequency-coded joint frequency modulation (FM) slope agile waveform. The intrapulse frequency-coded joint FM slope agile waveform is first designed. The delay inserted between subpulses makes the waveform easy to implement in engineering, and the ambiguity function diagram of the waveform approximates the ideal thumbtack type. Next, the echo slices are classified in the fractional domain utilizing the discontinuity of ISRJ and the focusing property of fractional Fourier transform for chirp signals. Then, the target and interference in the interfered echo slices are reconstructed by compressed sensing, and a time-domain filter is constructed based on interference-free echo slices. Finally, the echo signal after interference suppression is further filtered in the time domain to degrade range sidelobes. Simulation results show that the proposed method can effectively suppress three typical types of ISRJ. Moreover, the probability of target detection after interference suppression exceeds 90% when the jamming-to-signal ratio equals 50 dB.

Phase unwrapping error identification and suppression method in φ-OTDR systems based on PELT-VMD-ARIMA

In phase-sensitive optical time-domain reflectometer (φ-OTDR) systems, phase unwrapping errors can distort vibration information. To address this issue, a phase unwrapping error identification and suppression method combining pruned exact linear time (PELT) changepoint detection, variational mode decomposition (VMD), and autoregressive integrated moving average (ARIMA) models, termed PELT-VMD-ARIMA, is proposed. Firstly, the principle of the proposed method is introduced, and its effectiveness is verified through a series of numerical simulation experiments. Next, piezoelectric transducers (PZTs) are employed as seismic sources in experiments involving single-frequency and chirp signals. Compared to the mean-shift method, the proposed method reduces the average root mean square error (RMSE) by 70.36% within 2δ range around the changepoints. Finally, the proposed method was validated through an active source seismic application. The results demonstrate the efficacy of the proposed method in identifying and suppressing phase unwrapping errors, thereby enhancing signal quality. This method enhances the vibration recognition capability of φ-OTDR systems, which facilitates precise distributed acoustic sensing applications.

Damage imaging method based on circular DE-IDT array for phased array data fusion

Plate-like structures, including composite material plates, are extensively employed in major engineering structures such as aerospace, high-speed rail, and civil engineering. The growing utilization of curved panel structures and the increasing complexity of these structures have emphasized the need for flexible sensors capable of efficient signal front-end reception. Addressing the limitations of conventional sensors made of brittle piezoelectric materials in adhering to the surface of structures for health monitoring, a self-developed flexible dielectric elastomer-interdigital transducer (DE-IDT) array is employed to achieve damage imaging in isotropic aluminum curved panel structures and orthotropic composite material plates using linear frequency modulation (chirp) signal excitation. In addition, a proposed fusion method is utilized to obtain weighted imaging results, and evaluation and analysis are performed using relevant indicators. Experimental findings highlight the improved imaging accuracy achieved through phased array data fusion using the linear chirp signal, attributed to its wideband characteristics and ability to capture more damage signals. Moreover, the effectiveness of the circular DE-IDT array for damage detection and imaging in curved panel structures and composite material plates is successfully verified.

A Power Combiner–Splitter Based on a Rat-Race Coupler for an IQ Mixer in Synthetic Aperture Radar Applications

Synthetic aperture radar (SAR) is a powerful tool in remote sensing applications that can produce high-resolution images and operate in any weather condition. It is composed of many RF components, such as the IQ mixer, which mixes the base chirp signal (IF) with the carrier signal (LO) and increases the bandwidth of the transmitted signal to twice the maximum frequency of the base chirp signal, reducing the workload of Programmable Field Gate Arrays (FPGA) and increasing the resolution of the SAR system. This research proposes a power combiner–splitter design that will be used as a supporting component to construct the IQ mixer in SAR applications based on a rat-race coupler. The measurement results show that the coupler has good S-parameter values. S11, S22, and S33 have a low reflection value below −17 dB, S13 has a high isolation value below −22 dB, and S21 and S31 have a low attenuation value below −4 dB with amplitude unbalance below 0.1 dB and phase unbalance below 1∘. The 150 MHz requirement bandwidth for the RF signal is also achieved.

Автоматическая интерпретация ионограмм наклонного зондирования на основе гибридных алгоритмов

The paper presents a method of interpreting data on oblique ionosphere sounding (OS) with a continuous chirp signal. Hybrid algorithms for automatic interpretation of ionograms by selected points with significant amplitude obtained during secondary data processing for various heliogeophysical conditions have been developed and implemented. For the conditions of the two-layer ionosphere, an interpretation method has been worked out which involves analyzing histograms for the distribution of points with significant amplitude, which fall into a model mask constructed from the results of modeling of the distance-frequency characteristic for propagation when it moves over the ionogram. For the multilayer ionosphere, the interpretation is based on the study of the ionogram amplitude relief. The algorithms for extracting tracks of signals reflected from sporadic layers are examined separately. We report the results of interpretation of ionograms obtained on the network of chirp sounding radio paths in the northeastern region of Russia.

Automatic interpretation of oblique sounding ionograms based on hybrid algorithms

The paper presents a method of interpreting data on oblique ionosphere sounding (OS) with a continuous chirp signal. Hybrid algorithms for automatic interpretation of ionograms by selected points with significant amplitude obtained during secondary data processing for various heliogeophysical conditions have been developed and implemented. For the conditions of the two-layer ionosphere, an interpretation method has been worked out which involves analyzing histograms for the distribution of points with significant amplitude, which fall into a model mask constructed from the results of modeling of the distance-frequency characteristic for propagation when it moves over the ionogram. For the multilayer ionosphere, the interpretation is based on the study of the ionogram amplitude relief. The algorithms for extracting tracks of signals reflected from sporadic layers are examined separately. We report the results of interpretation of ionograms obtained on the network of chirp sounding radio paths in the northeastern region of Russia.

Photonic generation of dual-band triangular chirps utilizing a monolithic integrated mutual injection laser and application in radars.

We propose and demonstrate a dual-band microwave photonic radar scheme based on a monolithic integrated mutual injection laser. Based on the photon-photon resonance (PPR) and the gain switching effect of the integrated laser, the C-/X-band triangular chirp signals with high-quality and comparable power at 4.75-5.25 GHz and 9.5-10.5 GHz are generated. In the current proof-of-concept experiment, the range resolution of the dual-band chirp signals can reach 16.9 cm, compared with the single-band chirp signal that cannot distinguish the targets. Through the application of a single integrated device and a transceiver module sharing a set of antennas, the dual-band microwave photonic radar system scheme improves the system integration.

An Identification Method of Corner Reflector Array Based on Mismatched Filter through Changing the Frequency Modulation Slope

The corner reflector is an effective means of interference for radar seekers due to its high jamming intensity, wide frequency band, and combat effectiveness ratio. Properly arranging multiple corner reflectors in an array can form dilution jamming that resembles ships, substantially enhancing the interference effect. This results in a significant decline in the precision attack efficiency of radar seekers. Hence, it is critical to accurately identify corner reflector array. The common recognition methods involve extracting features on the high-resolution range profile (HRRP) and polarization domain. However, the former is constrained by the number of corner reflectors, while the latter is affected by the accuracy of polarization measurement, both of which have limited performance on the identification of corner reflector array. In terms of the evident variations in physical structures, there must be differences in their scattering characteristics. To highlight the differences, this paper proposes a new method based on the concept of mismatched filtering, which involves changing the frequency modulation slope of the chirp signal in the filter. Then, the variance of width and intervals within a specific scope are extracted as features to characterize these differences, and an identification process is designed in combination with the support vector machine. The simulation experiments demonstrate that the proposed method exhibits stable discriminative performance and can effectively combat dilution jamming. Its accuracy rate exceeds 0.86 when the signal-to-noise ratio is greater than 0 dB. Compared to the HRRP methods, the recognition accuracy of the proposed algorithm improves 15% in relation to variations in the quantity of corner reflectors.

Chirp-coded ultrasound for localization of linear and nonlinear scatterers in isotropic media

Chirp-coded ultrasound has been under active research for reciprocal Time Reversal with Nonlinear Elastic Wave Spectroscopy for ultrasonic wave focusing and additionally detection and analysis of nonlinear defects. Localization and imaging of defects under these principles, without scanning or use of other complicated methods, is an open problem. Frequency Modulated Constant Wave technology is widely known in radar applications where the distance to multiple reflecting targets, their velocities and angles of return are found from the chirp signal. These principles are not yet widely used in ultrasound technology. Chirp-coded ultrasound is common between the two methods and enable to maximize total power on target due to longer transmitted signals (as opposed to pulsed operation). This work proposes to unite the Frequency-Modulated Constant-Wave scatterer localization with reciprocal Time Reversal – Nonlinear Elastic Wave Spectroscopy principles to enable the localization of scatterers distant from the transducers and the analysis of their nonclassical nonlinearity which often can be caused by microdamage or cracking. In this paper only the first part (localization of scatterers using frequency-modulated constant wave ultrasound) of the problem is investigated. The main goal is to verify the feasibility of the method for ultrasound in solids and identify the main problems to be solved. Physical experiments and simulations are used to ascertain the detectability of linear and nonlinear scatterers in an isotropic solid medium (acrylic) using ultrasound. Potential problems with this approach are identified, to be solved in future work. In the future, this approach could enable to spatially filter the return signals, enabling to use reciprocal time reversal for focusing the wave energy in space directly onto selected scatterers, using the simplest of test setups: one transmitting and two receiving transducers.

Air-coupled ultrasonic inspection of resin materials using single-probe vertical reflection method

Air-coupled ultrasonic inspection is a noncontact and convenient nondestructive testing method. However, its vertical reflection method using a single probe (i.e., pulse-echo mode) is known to be difficult to achieve, even though it is frequently used inspection mode in conventional contact or water immersion ultrasonic testing. This is because the reflectivity of ultrasonic waves at the boundary between air and the surface of inspection object is enormous, and faint signals received after transmitting into the object are difficult to detect. In this study, in order to achieve the air-coupled ultrasonic single-probe reflection method, transmitting chirp signals (waves with a linearly frequency modulation) with an appropriate window function and applying a pulse compression technique (a cross-correlation process between the received signal and a reference chirp signal) was examined, and its effectiveness was investigated through experiments for polystyrene specimens. Experimental results showed that the proposed method was effective in detecting faint reflection signals after propagating through the specimens, and that the difference in plate thickness could be detected by observing the change of the signal-receiving period of multiple reflection signals between the top and bottom surfaces of the specimens. These results demonstrate the feasibility of nondestructive testing using the air-coupled ultrasonic vertical reflection method and could show an important step toward its future practical applications.

Method for Onboard X-Band Chirp Signal Compensation of Micro SAR Satellites and Verification

Method for Onboard X-Band Chirp Signal Compensation of Micro SAR Satellites and Verification