Electronic Countermeasures Research Articles

A Sparse Imaging Method for Frequency Agile SAR

Frequency agility increases the difficulty of jammers to predict and estimate the carrier frequency and, thus, improves the radar electronic counter-countermeasures (ECCM) performance. In this article, frequency agility is introduced into synthetic aperture radar (SAR). The characteristic of the Doppler history of frequency-agile SAR (FASAR) is analyzed, which shows that the azimuth compression could not be achieved by the classic imaging algorithms. In order to reconstruct the images of interested targets, a three-channel sparse imaging method is proposed based on approximated observation model by using the echo data of different carrier frequencies. By deriving the equivalent observation model, it is concluded that the reconstruction performance can be enhanced by improving the coherence of match filter imaging results in different channels. The image characteristic of different channels in FASAR is analyzed based on the chirp scaling imaging operator. A phase compensation method is then proposed to improve the coherence of images of interested targets in different channels. Specifically, the SAR mode of random frequency agility is proposed to improve the reconstruction performance. Finally, simulations are carried out to demonstrate the effectiveness of imaging methods and ECCM performance. Theoretical analysis and simulation results demonstrate that images generated in random FASAR have better performance than those in stepped FASAR. By performing the phase compensation, the reconstruction performance of small targets can be significantly improved.

Air Moving Target Imaging for Staggered ISAR

The rapid development of the modern electronic counter-countermeasures (ECCMs) has made the conventional inverse synthetic aperture radar (ISAR) associated with the regular signal waveforms more vulnerable and unreliable. To deal with this issue, the complex waveform designment with staggered pulse sampling is developed in an ISAR system in this letter. In the proposed method, the generalized time-scaled transform (GTST) is adopted to effectively accomplish the irregular signal reconstruction and linear phase decoupling. After that, a set of matched filtering functions are established and interspersed in the imaging processes to accomplish the subsequent motion compensation, target imaging, and range and cross-range scaling. Finally, a satisfied ISAR imagery corresponding to the real size of a moving target can be recovered. The simulation and real-measured radar data processing results are applied to demonstrate the effectiveness of the proposed method.

Operational Effectiveness Evaluation of EW Equipment System Based on Framework Design

The currently used evaluating method has such problems as complex evaluation index space, complexity of computation, low evaluation efficiency, and low systematicness and intellectualization, which is difficult to meet the requirements of operational effectiveness evaluation for ECM equipment. In order to guarantee the efficiency and accuracy of operational effectiveness evaluation, an integrated and systematic evaluation method was provided based on multi-views system’s simulation model architecture, which can show the actual frameworks of equipment system for evaluation, we describe the element, structure, operational process and index system in a standardized manner. Furthermore, a framework of Flexible-intelligent Evaluation towards Combat-capability Space in System-of-systems (FECSS) was proposed. The FECSS method builds a bi-directional mapping relation between the upper and low operational effectiveness indicators by basic indicators-formed space in system-of-systems which combined the complex evaluation index, evaluation process with intelligent evaluation model. The proposed method can effectively analysis the effectiveness results in condition of different types and numbers of equipment. It also makes the electronic countermeasure equipment project demonstration and operational application more feasibly and practically.

Deep ToA Mask Based Recursive Radar Pulse Deinterleaving

In a complex electromagnetic environment, multiple radar signals of various modes are densely interleaved. In this environment, radar parameters overlap seriously and change continuously over time. Traditional radar pulse deinterleaving algorithms face severe challenges such as parameters missing, pulse jitter, and the increasing number of electronic countermeasure devices. In this paper, we propose a recursive deinterleaving algorithm based on blind signal separation and deep learning to cope with such a situation. The Recursive Deinterleaving Network (RDN) of Deep ToA Mask (DTM) maps the ToA train to a suitable feature space first. ToA coefficient masks of each radar emitter are estimated with the local and global context information of the radar pulse feature. Then the RDN sorts out several radar pulse trains recursively with the help of dual-path attention. It also predicts the number of emitters with nearly 100% accuracy and handles the unknown Pulse Repetition Interval (PRI) situation. More accurate pulse deinterleaving results can be obtained if the DTM utilizes more radar parameters through proper pre-processing fine-tuning and post-processing re-clustering. The processing steps of the DTM are introduced in detail. The simulation shows it can achieve 97% sorting accuracy for multi-pulse interleaved radar train with jitter PRI and pulse missing. The DTM algorithm can also deal with the interleaved radar signals of different PRI modulations by re-clustering with noisy PDW information. On the premise of knowing the modulation type or PRI information, the pulse train deinterleaving accuracy of multi-modulation emitters is higher.

A Truncated Matched Filter Method for Interrupted Sampling Repeater Jamming Suppression Based on Jamming Reconstruction

Interrupted sampling repeater jamming (ISRJ) is becoming more widely used in electronic countermeasures (ECM), thanks to the development of digital radio frequency memory (DRFM). Radar electronic counter-countermeasure (ECCM) is much more difficult when the jamming signal is coherent with the emitted signal. Due to the intermittent transmission feature of ISRJ, the energy accumulation of jamming on the matched filter shows a ‘ladder’ characteristic, whereas the real target signal is continuous. As a consequence, the time delay and distribution of the jamming slice can be obtained based on searching the truncated-matched-filter (TMF) matrix. That is composed of pulse compression (PC) results under matched filters with different lengths. Based on the above theory, this paper proposes a truncated matched filter method by the reconstruction of jamming slices to suppress ISRJ of linear frequency modulation (LFM) radars. The numerical simulations indicate the effectiveness of the proposed method and validate the theoretical analysis.

Functional flexible photonics-assisted frequency measurement based on combination of stimulated Brillouin scattering and a Mach – Zehnder interferometer

A functional flexible photonics-assisted frequency measurement (PFM) is proposed. Owing to polarisation multiplexing, the electro-optic (O/E) conversion can be performed in a single optical path, which endows the system high stability and concise configuration. Moreover, using a specially designed functional coarse/accurate frequency measurement (C/AFM) module, a large covering range, moderate accuracy, and fast response frequency measurement results can be ensured in a radar warning receiver (RWR), whereas high accurate results can be used in an electronic countermeasures receiver (ECMR). The simulation results show that a strict monotonous amplitude comparison function (ACF) can be constructed based on the structure of a Mach – Zehnder interferometer (MZI) to map the signal frequency, with a measurement error of less than 0.2 GHz in the range of 1 – 31 GHz. This coarse measurement results can be used to perform radar warning. Based on this result, a highly accurate frequency measurement result is achieved through stimulated Brillouin scattering (SBS). The results reveal that the accuracy is improved to better than 20 MHz. Noteworthy, the C/AFM module consists of purely passive devices, which makes this system meet the potential of integration.

An Enhanced Algorithm for Deinterleaving Mixed Radar Signals

An essentialtask of the electronic support measures system is to deinterleave the intercepted radar pulse stream. To improve the radars’ antijamming capability and adapt the radars to different application scenarios, the pulse signals emitted by various radars are becoming abundant, causing the pulse stream intercepted by the reconnaissancereceiver to becomemore and more complicated. Apart from fixed pulse repetition interval (PRI) signals, other PRI modulated signals, such as jitter PRI and staggered PRI, also appear in the intercepted radar pulse stream. The aforementioned pulse stream is defined as mixed radar signals in this article. The deinterleaving of mixed radar signals is an inevitable challenge in the field of electronic countermeasures. A novel algorithm for deinterleaving mixed radar signals is proposed in this article. It is flexible for deinterleaving different PRI modulated signals. A sequence retrieval method based on clustering ideas is also proposed in the algorithm, which enables different pulse sequences to be accurately separated. Simulation results show that the new algorithm has great PRI estimation accuracy for mixed radar signals in a large pulse missing rate.

Design and Simulation of 10-GHz Bandwidth Phase-Velocity Tapers Folded Waveguide for 108-GHz Continuous-Wave Traveling-Wave Tube

Folded waveguide (FW) traveling-wave tubes (TWT) is a typical kind of vacuum electron device (VED) with some unique characteristics of high frequency, high power, and moderate bandwidth, which are widely used in radars, communication systems, electronic countermeasure, and so on. For the application to the demonstrations of ocean communication with the frequency of over 100 GHz and continuous-wave power with 15 W, an FWTWT operating at the frequency of 108 GHz and the CW power with 50 W is designed. The optimizations of dispersion characteristics and structural parameters of this FWTWT are optimized through a detailed theoretical analysis and a particle-in-cell (PIC) simulation, respectively. For the improvements of communication quality by the increase of output power, a novel method of phase-velocity tapered (PVT) FW slow wave structure (SWS) is used. Comparing with the conventional FWSWS, the output power with the proposed scheme is enhanced 1.5 times. Moreover, the effects of angle and kinetic spreads of electron beam velocity on output power are first investigated using PIC simulations. On the other hand, for obtaining the optimum signal transmission, a tapered and modified pill-box window is presented and used as the transmission structure, which is the characteristics of the broad bandwidth and low attenuation of transmission. With the help of optimized parameters, the CW FWTWT operates at the frequency of 108 GHz, and the maximum output power, gain, and bandwidth are obtained at 78.6 W, 31.9 dB, and 11 GHz, respectively. The optimum results are beneficial to the development of CW FWTWT.

Unsupervised Clustering Method to Discriminate Dense Deception Jamming for Surveillance Radar

With the development of digital radiofrequency memory devices, the deception jamming has become a major jamming type in radar electronic counter countermeasures, especially the dense deception jamming. Recent years, some methods using signal features are proposed for specific deception jamming excision scene. It verifies the feasibility that uses signal features to discriminate deception jamming. However, discriminator training and simulation are indeed hard to achievable since no jamming samples can be obtained in advance. In this letter, we focus on the online dense deception jamming discrimination problem without the offline data training. Since deception jamming signals generated by jammers are definitely different from physical backscattering target echoes on signal features and dense jamming signals generated by one jammer has similar signal fingerprint features, an unsupervised clustering method with heuristic feature extraction is proposed. All discrimination processes are data driven and can be executed online without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> information. To evaluate its effectiveness, the proposed method is applied to a group of experimental data collected from a trial <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band radar. Results corroborate the proposed method and indicate the direction of future research.

Bandwidth superposition of linearly chirped microwave waveforms based on a Fourier domain mode-locked optoelectronic oscillator

Optoelectronic oscillators (OEOs) are promising for radar, communication and electronic countermeasure systems. Among them, frequency-scanning OEOs with wide instantaneous bandwidth are needed for many advanced applications. In this work, we demonstrate a novel system to generate bandwidth-doubled linearly chirped microwave waveforms (LCMWs) based on bandwidth superposition using a Fourier domain mode-locked OEO (FDML OEO). In the proposed system, bandwidth-doubling is achieved by re-modulating the generated LCMW of the FDML OEO onto a frequency-scanning optical carrier signal with the help of an external Mach-Zehnder modulator. LCMWs with wide frequency scanning instantaneous bandwidth of 10 GHz are experimentally obtained. Meanwhile, these LCMWs are tunable in an ultra-wide frequency range from 1 to 39 GHz. Moreover, they are with high frequency sweep linearity of 0.5%. Our work presents a simple method to generate tunable wide-band LCMWs for potential microwave sources.

A multiband metamaterial absorber for GHz and THz simultaneously

Nowadays, more and more metamaterial absorbers (MMAs) are explored not only in the microwave band but also in terahertz band, but few studies concentrate on metamaterial absorbers which can work in cross-band, that to say, absorb gigahertz (GHz) and terahertz (THz) electromagnetic (EM) waves simultaneously. This paper proposed a design concept of MMA which can realize the absorption in GHz-band and THz-band simultaneously, and designed a cross-band metamaterial absorber (CMMA). The proposed CMMA can achieve three absorption peaks in GHz-band and two absorption peaks in THz-band. The characteristic of simultaneous absorption to GHz and THz waves render the CMMA widely used in multi-band electromagnetic stealth and electronic countermeasures, and the superposition design concept provides a novel idea for designing cross-band absorber.

Deep Learning Approach in DOA Estimation: A Systematic Literature Review

In array signal processing, the direction of arrival (DOA) of the signal source has drawn broad research interests with its wide applications in fields such as sonar, radar, communications, medical detection, and electronic countermeasures. In recent years, the application of deep learning (DL) to DOA estimation has achieved great success. This study provides a systematic review of research on DOA estimation using deep neural network methods. We manually selected twenty-five papers related to this research from five prominent databases (SpringerLink, IEEE Xplore, ScienceDirect, Scopus, and Google Scholar) for exploration. Six questions describing the overall trend of DOA estimation using deep learning are put forward. Then, we answered these questions by reviewing the literature. This review is helpful for researchers in this field because it provides more specific and comprehensive information needed for future research. Specifically, we first analyzed the background of the selected papers, including the type of publication, the number of citations, and the country of origin. Then, the DL technology used in DOA estimation is systematically analyzed, including the purpose of using DL in DOA estimation, various DL models (convolutional neural network, deep neural network, and combination network), and various DOA estimation schemes. Finally, various evaluation criteria (root-mean-squared error, accuracy, and mean absolute error) are used to evaluate the DL technology in DOA estimation, and various factors (signal-to-noise ratio, number of snapshots, number of antennas, and number of signal sources) affecting DOA estimation are analyzed. Based on our findings, we believe that deep learning can perform DOA estimation well, and there is still room for improvement in deep learning technology. In this study, the factors affecting DOA estimation can be used as the direction for researchers to conduct in-depth research.

Pangolin-Inspired Stretchable, Microwave-Invisible Metascale.

Microwave-invisible devices are emerging as a valuable technology in various applications, including soft robotics, shape-morphing structures, and textural camouflages, especially in electronic countermeasures. Unfortunately, conventional microwave-absorbing metastructures and bulk absorbers are stretching confined, limiting their application in deformable or special-shaped targets. To overcome such limitations, a conceptually novel soft-rigid-connection strategy, inspired by the pangolin, is proposed. Pangolin-inspired metascale (PIMS), which is a kind of stretchable metamaterial consisting of an electromagnetic dissipative scale (EMD-scale) and elastomer, is rationally designed. Such a device exhibits robust microwave-absorbing capacity under the interference of 50% stretching. Besides, profiting from the covering effect and size-confined effect of EMD-scale, the out-of-plane indentation failure force of PIMS is at least 5 times larger than conventional device. As a proof of concept, the proposed device is conformally pasted on nondevelopable surfaces. For a spherical dome surface, the maximum radar cross-section (RCS) reduction of PIMS is 6.3dB larger than that of a conventional device, while for a saddle surface, the bandwidth of 10dB RCS reduction exhibits an increase of 83%. In short, this work provides a conceptually novel platform to develop stretchable, nondevelopable surface conformable functional devices.

Newtonalized orthogonal matching pursuit for the linear frequency‐modulated pulse frequency agile radar

The linear frequency-modulated frequency agile radar (FAR) can be used for synthesizing high-range-resolution profiles (HRRP), and also has excellent electronic counter-countermeasures performance. Similar to the Newtonalized orthogonal matching pursuit (NOMP) for line spectral estimation problem, the NOMP for the FAR radar termed as NOMP-FAR is designed to process each coarse range bin to extract the HRRP and velocities of multiple targets, including the guide for determining the oversampling factor and the stopping criterion. In addition, it is shown that the target will cause false alarm in the nearby coarse range bins, and a post-processing algorithm is proposed to suppress the ghost targets. Numerical simulations are conducted to demonstrate the effectiveness of NOMP-FAR.

Optimal design of anti‐interrupted sampling repeater jamming waveform for missile‐borne radar based on an improved genetic algorithm

The optimal design of transmitted waveforms to improve the performance of missile-borne radar in suppressing interrupted sampling repeater jamming (ISRJ) is studied here. The waveform diversity property requires that the waveform group has excellent orthogonality (good auto- and cross-correlation properties), which is an effective waveform optimisation design method for missile-borne radar electronic counter-countermeasures. The principle of orthogonal phase coding waveform against ISRJ is studied and the use of chaotic sequences is proposed to initialise the population, as well as a simulated annealing selection operator, which improves the convergence speed of the improved genetic algorithm (IGA) and enhances the global optimisation ability. The IGA improves the shortcomings of GA, that is, easily falling into a local optimum and slow search speed, and can realise a global search for longer orthogonal polyphase coding sequence sets. The simulation examples demonstrate the good jamming suppression performance of the proposed method.

Tailoring high-electroconductivity carbon cloth coated by nickel cobaltate/nickel oxide: A case of transition from microwave shielding to absorption

The development of electromagnetic wave (EMW) shielding and absorbing materials for flexible devices with carbon cloth and cotton cloth as the substrate has been widely reported. However, the utilization of incorrect test methods in recent reports led to the test data erroneously exhibits the actual absorption performance of the flexible absorber, which confuses the cognition of shielding and the absorbent. Moreover, previous studies are mostly based on semi-empirical rules and lack data relationships between absorption and characterization. The dominant dissipation mechanism in EMW absorbent materials demands to be resolved. Hence, we compared the EMW absorption capacity of the hierarchical carbon cloth@NiCo2O4/NiO hybrid via the waveguide method and the coaxial method. Specifically, the flexible absorber with integrated structure is unfavorable for incident waves to enter its interior due to its skin depth and extremely high conductivity. However, the absorbers made into a paraffin ring showed obvious optimization. Enhanced interfacial polarization is confirmed as the dominant mechanism of EMW dissipation via various characterization and analysis of electromagnetic (EM) parameters. This work provides an insight into the misunderstanding of the rational design of flexible absorbent materials for the first time, which is of great significance to the research of flexible electronic countermeasure materials.

Specific emitter identification based on CNN

Specific emitter identification is one of the important technologies of electronic countermeasures. The convolutional neural network (CNN) has a strong ability to process image classification. To solve the problem that the bispectral feature of the radiation source does not perform well in the specific emitter identification, this paper proposes a method of combining the two-dimensional bispectrum of the radiation source and CNN. In order to test the performance of the method, this article designed a semi-physical system to collect the radiation source signal. It is verified by experiments that this method has a 92.4% correct rate for identifying different radiation source signals. Compared with other algorithms that combine bispectral features, the proposed method has advantages in accuracy and complexity.

Deception electronic counter‐countermeasure applicable to multiple jammer sources in distributed multiple‐radar system

Deception jamming poses a fatal threat to the radar performance, and its jamming performance has been greatly improved through networking. However, available deception electronic counter-countermeasure (ECCM) methods are mostly developed in the scenario of a single jamming source. Therefore, it is of great importance to develop deception ECCM methods that can counter multiple jammers. This work proposes a deception jamming discrimination method applicable to multiple jammer sources in distributed multiple-radar system, based on the correlation coefficient between different target-received signal vectors. The false targets generated by one jammer are highly correlated, while a radar target is uncorrelated with either other radar targets or false targets. For the estimated correlation coefficient, the Fisher z-transformation is applied to determine the correlation between targets with the Z-test. Since the jammer usually generates multiple false targets at once to enhance its deceptions, a target can be judged as a false target when multiple targets are highly correlated with it; otherwise a radar target is declared. More importantly, compared with existing methods, no prior information is required here. Simulation results corroborate the feasibility of the proposed discrimination method and its performance due to the influence of jamming-to-noise ratio. The spatial correlation of radar targets and geometry conditions are covered.

Photonic-Assisted Microwave Frequency and Phase Shifter for Deception Jamming

A new microwave photonic signal processing structure that has the ability to realise frequency and phase shifting operation is presented. The proposed structure uses Serrodyne phase modulation in a dual-polarisation binary phase shift keying (DP-BPSK) dual-drive Mach Zehnder modulator to shift the frequency of an input microwave signal. This has the advantage over the conventional frequency mixers that the unwanted frequency components adjacent to the frequency translated microwave signal can be largely suppressed. It is suitable for use in deception jamming in electronic countermeasures systems. The phase shifting operation is realised by controlling the bias voltages of the DP-BPSK modulator. The dual-function microwave photonic signal processor has a simple structure and a wide bandwidth. The structure enables commercial modulator bias controllers to be used to provide long-term stable performance. Experimental results are presented that demonstrate a wide operating frequency range of 3 to 16 GHz, an over 35 dB suppression on the spurious signals and 0° to 360° phase shift on the frequency translated microwave signal. Using bias controllers to maintain a large spurious suppression ratio of around 35 dB is also demonstrated.

Range Sidelobe Suppression for Randomized Stepped-Frequency Chirp Radar

Randomized stepped-frequency (RSF) radar, which transmits pulses with random carrier frequencies in a coherent processing interval, has an excellent electronic counter-countermeasures performance and the ability to generate the high-range-resolution profiles (HRRPs) of target with a narrow bandwidth receiver. Due to the random nature, the choice of carrier frequencies in RSF radar is usually an undersampling of available frequencies, which make the HRRP generated by matched filtering suffer from high noise-like sidelobes. In this article, we take the sinc-envelopes formed by linear-frequency-modulation pulses as well as RSF phases into account, and propose a novel (or generalized) range sidelobe suppression filters design method for RSF chirp waveform based on convex optimization (the model is transformed into a second-order cone program). By using these filters, the target HRRP with much lower sidelobes can be obtained, and the performance can be traded with the instantaneous bandwidth of the receiver, which provides a new idea for solving the sidelobe problem in RSF radar.