Abstract:The electromagnetic spectrum is the sixth dimensional battle space after land, sea, air, space and cyber, and runs through the other five dimensional battles. In order to effectively deal with the challenges and threats of the electromagnetic spectrum, the US Department of Defense puts forward the concept of electromagnetic spectrum operations, which has a profound impact on future combat patterns and even war forms. From the perspective of electromagnetic spectrum application, the application status and representative work of the US Department of Defense on electromagnetic spectrum are systematically introduced. Firstly, the traditional military applications of the electromagnetic spectrum are systematically sorted out, such as communications, radar, signals intelligence, infrared sensors, electronic warfare, navigation warfare. Secondly, the emerging military applications of the electromagnetic spectrum are emphatically introduced, such as 5G communications, artificial intelligence applications, laser communications, directed-energy weapons, anti-UAV systems and emerging concepts. Finally, the strategies and policies of the electromagnetic spectrum made by the US Department of Defense are summarized, and some suggestions are put forward to strengthen the operational capability of electromagnetic spectrum.

Abstract:In the electromagnetic space,the physical domain and information domain cannot be effectively integrated and the application of electromagnetic information lacks intelligence. A concept of intelligent electromagnetic space is put forward. The intelligent electromagnetic space should bear the ability of representation, understanding, predicting and decision making. Taking the model as the core, taking the software as the carrier, with highly data-driven, it can achieve accurate mapping of the physical world and provide intelligent decision-making services for the combat command and troop operations. According to the organization mechanism of electromagnetic space information, the problem of multi-source heterogeneous physics—information data fusion is further solved, and the technical framework is constructed. Some key technologies and implementation ideas are proposed,including Geographic Coordinate Subdividing Grid with One Dimension Integral Coding on 2n-Tree-N Dimensions(GEOSOT-ND) high-dimensional tensor modeling and computation, multi-domain electromagnetic space sensing and efficient storage, full-dimensional electromagnetic situation reconstruction and intelligent deduction, and grid data-driven application methods.

Abstract:There exist the following problems in the available methods for Direct Position Determination(DPD) of Non-Circular(NC) sources with multiple base stations: high computational complexity of spectral peak search, sensitivity to the location of base stations, and lack of consideration of the difference in signal loss when propagating in space, which leads to unstable performance. A DPD method is proposed for NC sources: Joint Reduced Dimension Propagator Method and Taylor Compensation(JRT-PM). First, the array aperture is expanded according to the elliptic covariance information of NC signals. Then, the NC phase search dimension is eliminated by the dimension reduction method for rough estimation to reduce the computational complexity. Next, the Taylor compensation is combined with the information of all base stations to improve the estimation performance of the algorithm. Simulation experiments show that compared with the traditional two-step localization algorithm by Angle Of Arrival K-means clustering(AOA-clustering), Minimum Variance Distortionless Response(MVDR) DPD method and Subspace Data Fusion(SDF) DPD method, the proposed algorithm can estimate more targets while improving the localization accuracy. Compared with Non-Circular Propagator Method(NC-PM) DPD method, the proposed algorithm significantly reduces the computational complexity while ensuring the estimation performance.

Abstract:Due to the diversity of RF signals, the complexity of the electromagnetic environment, and the difficulty of feature extraction, the robustness and applicability of the existing artificial features-based RF-specific emitter identification methods cannot meet the application requirements. Although the data-driven deep learning methods can provide a more flexible mode of specific emitter identification, they are less interpretable and lack a general test mode to evaluate their advantages and disadvantages. An evaluation method is explored for the deep learning model on the target individual dataset of the Electromagnetic Big Data Super Contest, and a general testing system architecture is proposed for the specific emitter identification model based on deep neural networks. The framework constructs the simulation test samples through signal feature masking, Generative Adversarial Network (GAN), deception signal collection, channel simulation and other methods, and imports the test samples and original data into the deep model to compare the recognition results. The test results are employed to judge the location of the signal key features extracted by the deep model, to analyze the robustness of the model, and to reveal the impact of the channel environment on the recognition performance, thus the performance of the deep learning model can be interpretable.

Abstract:As an important means of managing and monitoring the electromagnetic spectrum, communication signal modulation recognition shows important research value and application prospects. A signal modulation recognition method based on complex neural network is proposed by using the frequency domain information of modulated signals for modulation recognition. Firstly, the I and Q signals are combined into complex signals, and the real and imaginary parts obtained are combined as the data set of the input network after Fast Fourier Transform(FFT). Secondly, a complex neural network structure is designed, and an attention mechanism is introduced to improve the network structure. Finally, the simulation results show that the proposed method can effectively identify nine modulation modes, and the average correct recognition rate reaches 96.33% when the signal-to-noise ratio is 6 dB.

Abstract:With the increasing complexity of the electromagnetic signal environment and the increasing number of communication devices, the interference with electromagnetic signals is gradually increasing. Therefore, the study on signal reception and processing techniques in different noise environments and the use of signal data indicators and the information they carry in complex electromagnetic environments is very critical. In order to understand the performance of noisy signals in different electromagnetic environments and improve the quality and reliability of signal utilization, a time series decomposition-based electromagnetic data processing method is proposed. A noisy signal processing model is established based on additive seasonal time series decomposition, and the model is also employed to analyze and evaluate the performance of signals in noisy environments with regularity, trend, BER, etc., and to data-mine the original information and carrier information. Compared with the traditional methods, the proposed time series decomposition-based signal mining and prediction model is more accurate for signal prediction in noisy environment.

Abstract:It is important to obtain the dielectric constant of materials in terahertz band for applications of 6G communication, radar remote sensing, detection and imaging. In this paper, the complex permittivity of samples is extracted based on the Newton Raphson(NR) iterative method, of which the influence of the initial value is analyzed. A set of 8f quasi optical system consisting of Vector Network Analyzer(VNA), spread spectrum module and four parabolic mirrors is built in 325~500 GHz(Y-band) to realize the free space measurement of scattering parameter S₂₁. The relationship between complex permittivity and S₂₁ is derived from the electromagnetic wave transmission model. The complex permittivity spectra of Teflon, ABS and PMMA samples are extracted by iterative method. The results are consistent with other literatures, which verify the effectiveness of the proposed system and the method.

Abstract:Due to the characteristics of good security, strong transmittance, and fingerprint characteristics, terahertz radiation has shown great application prospects in the fields of non-destructive detection, radar imaging, space communication, etc., which makes it unabated in current scientific research. With the characteristics of quantum anomalous Hall effect, topological protection of zero band gap, ultra-high carrier mobility, etc., the Dirac semimetals exhibit extraordinary characteristics in the field of terahertz detection, which provides a great platform for the exploration and realization of room temperature terahertz detector. In this paper, the research status of terahertz photodetectors based on the Dirac semimetal materials is introduced, and the device performance and detection mechanism are mainly discussed.

Abstract:The optical fiber communication technology is adopted to transmit data image with high frame rate and high resolution in order to improve the anti-interference, transmission speed and bit error rate of the photoelectric tracking equipment. The long-distance transmission technology is mainly utilized in this design for Cameralink high-speed digital images, a full-mode Cameralink digital image optical transceiver end is studied based on Field-Programmable Gate Array(FPGA), including FPGA chip, Cameralink interface module, Small Form-factor Pluggables(SFP) optical module, Cameralink decoding module, mode control module. The functions of each module are mainly as follows: Cameralink interface module is utilized to receive Cameralink information and send the received information to Cameralink decoding module; Cameralink decoding module decodes the serial data and sends it to the serial-parallel signal conversion module; the signal conversion module performs serial-to-parallel conversion on the received digital image signal to form a serial data stream; the SFP optical module receives the serial data stream and converts it into an optical fiber signal; the mode control module controls the working mode of the transmitting end. This design can realize the data transmitting and receiving of infrared image in resolution of 640×512 and a frame rate of 100 Hz. It has finished several environment tests and is applied in engineering.

Abstract:Low integration and poor interoperability of existing unmanned aerial vehicle tracking telemetry and command terminals could not satisfy the development trends of modularization, integration and universality of Unmanned Aerial Vehicle(UAV) in the future. An integrated design which can be applied to both airborne and ground UAV Tracking Telemetry and Command(TT&C) terminals is proposed. It adopts the mode of combing "high-integrated system" with "comprehensive reconfigurable function". Standard modules are utilized to build an open hardware platform, which can achieve high-integrated processing capability. The dynamic reconstructed loading mechanism of communication waveform is designed to complete the online update and upgrade of the communication system in the universal TT&C link. The research of standardized communication protocol provides the interconnection basis for different types of TT&C links. The experimental results show that the design can complete the dynamic reconstruction in a few minutes and effectively support different missions.

Abstract:In the traditional Multiple Hypothesis Tracker(MHT) algorithm, it is usually assumed that the clutter intensity is known a priori. When the clutter of observation scene is unknown and spatially variable, the performance of the tracking algorithm drops sharply. To solve this problem, an improved MHT method with clutter estimation based on adaptive Gaussian Mixture Model(GMM) is proposed. Firstly, the adaptive GMM is utilized to fit the spatial distribution of unknown clutter, and the clutter intensity in the gate is estimated adaptively. Then, it is applied to the MHT tracker to effectively improve the accuracy of track score calculation and optimal hypothetical track estimation, so as to realize stable tracking in unknown clutter scene. Simulation results show that the proposed algorithm achieves better data association accuracy and track maintenance performance than the standard MHT algorithm and the MHT-GMM algorithm in unknown clutter observation scene.

Abstract:The overall construction of the intelligent railways should be promoted in order to facilitate the digital transformation of railways. Taking the Xiamen North Station as the scenario and combining with the actual situation of China's railways, the channel characteristics of Global System for Mobile Communications-Railway(GSM-R), 5G-Railway(5G-R) and millimeter wave communication systems based on high-performance ray tracing at the four frequency bands of 932 MHz, 2.1 GHz, 41 GHz and 84.25 GHz are studied. Relying on high-performance Ray Tracing(RT) simulation, the radio propagation characteristics of high-speed rail station scenarios under different frequency bands are accurately modeled, and then the multi-dimensional channel characteristics under multi-band multi-standard are compared and studied. The outcomes indicate that as the radio frequency increases, the wireless signal coverage becomes smaller. And the less the multipaths generated by scatterers, the weaker the dispersion of multipath signal will be in the time and space domains. The research can provide theoretical basis and data support for the design and optimization of the railway dedicated mobile communication system for the high-speed railway station scenario.

Abstract:S-band High Power Microwave(HPM) is employed to produce the plasma in the atmosphere environment simulation chamber. The experiment researches on Ka-band microwave propagating characteristics in atmospheric plasma are performed, and the Ka-band microwave attenuation characteristics of atmospheric plasma are obtained. Some novelty propagation characteristics in the interaction of electromagnetic wave and atmospheric plasma are found: the electromagnetic wave transmission signal enhancement effect appears oscillation on Ka-band; the maximum value of propagation enhancement is almost 2 times, and the period of oscillation is 80 MHz. The phenomenon of propagation enhancement also occurs with the enhancing of buffer gas pressure, but the amplitude decreases. The reasons of propagation enhancement are analyzed. The research results provide important technical support for the application of plasma in stealth and black barrier communications.

Abstract:A Composite Right/Left-Handed Transmission Line(CRLH TL) structure based on probe-loaded Complementary Split-Ring Resonator(CSRR) is proposed in this paper. Based on the resonant characteristic of CSRR and CRLH structure, the transmission zeros are introduced and the size of the filter is reduced by extending the length of CRLH coupling slot and by increasing the number of short-circuit probes in CSRR. The filter is designed with wide bandwidth, high selectivity and miniaturization. The prototype of the band-pass filter is fabricated. The overall size of the prototype is 30 mm×15 mm×1.35 mm. The test results show that the center frequency and insertion loss of the filter are 6.6 GHz and 0.65 dB respectively, and the 3 dB bandwidth of the filter is 9.3 GHz. The filter shows a good application value in microwave systems such as wireless communication and navigation.

Abstract:With the rapid improvement of clock frequency in electronic system, crosstalk has become one of the problems that Printed Circuit Board(PCB) designers must concern. Although the design cost has been cut to a certain degree, it still takes a lot of time to simulate the crosstalk on PCB even with the help of high-speed circuit simulation software. Aiming to improve the efficiency of PCB crosstalk prediction, a new data structure is proposed to describe PCBs. The factors that cause crosstalk on PCB are comprehensively analyzed, and a PCB crosstalk prediction system is built by using Natural Language Processing(NLP), which reduces the time for crosstalk prediction to the magnitude of seconds and achieves 73.2% accuracy.

Abstract:Based on key technologies such as 5G base station forward power control and beam forming, the electromagnetic radiation test scheme for 5G base station under the condition of single user is designed. According to the regular layout of electromagnetic radiation power density decreasing with the square of distance, the test efficiency of macro base station can be improved to some extent. In addition, field measurement of the proposed monitoring scheme shows that the monitoring results are far less than the limit value of International Commission on Non-Ionizing Radiation Protection(ICNIRP) standard, indicating that the electromagnetic radiation level of 5G base station is generally controllable. Finally, High Frequency Structure Simulator(HFSS) is adopted to design the 5G base station antenna model to obtain the large-scale Multiple-Input Multiple-Output(MIMO) antenna array direction map, and the scene is built based on the electromagnetic parameter analysis of the actual scene. The electromagnetic radiation of 5G base station is predicted by ray tracing algorithm. The prediction results show little error compared with the monitoring results, which proves the reliability of the prediction method.

Abstract:The mechanical vibration or rotation of the target or its components produces the micro-Doppler effect, which plays an important role in target classification and recognition. However, the micro-Doppler effect of many objects in the environment (such as wind turbines, air conditioners, etc.) is like time-varying clutter to the radar system, leading to false alarms. In this paper, aiming at the problem that micro-Doppler clutter may interfere with passive radar target detection, a micro-Doppler clutter suppression method based on the improved Sparsity of Adaptive Matching Pursuit (SAMP) is proposed. Considering the sparse characteristics of the micro-Doppler clutter, this problem can be transformed into a sparse signal representation problem, and the purpose of suppressing the micro-Doppler clutter is achieved by separating the signal. Compared with the original SAMP algorithm, the improved SAMP algorithm can quickly stop iteration after the residual reaches the adaptive threshold. Simulation and measured data verify the effectiveness of the proposed method.

Abstract:There are many noise points in the 3D point cloud dala obtained by Time Of Flight (TOF) and the proportion of real objects in the point cloud is small. An iterative closest point registration algorithm based on intensity feature matching is proposed for TOF point cloud data. Firstly, the intensity feature is employed to extract the effective region, and then the effective region is configured. Finally, the change matrix of the effective region is utilized to register the whole point cloud data. Experimental results show that this method can effectively improve the registration accuracy of real target point cloud without affecting the registration speed.