Abstract:With the development of next-generation communications and equipment towards wider bandwidth and higher accuracy, millimeter wave and terahertz band has become the research focus of microwave technology. Transmit power is a significant figure of terahertz system, which directly determines the operating distance. Millimeter wave and terahertz solid-state power devices reveal great advances recently, and the engineering realization of terahertz solid-state power amplifiers at home and abroad is promoted. In this article, the international research status of millimeter wave terahertz power combining technology and solid-state power amplifier is introduced, and the latest research progresses of solid-state power amplifier modules based on radial combining, rectangular waveguide combining and silicon waveguide combining at W and G band in China, especially in Nanjing Electronic Devices Institute, are concluded.

Abstract:With the wide application of high performance composites in aerospace, military and other high-tech fields, more and more attention has been paid to the quality and performance inspection of composites. How to conduct Nondestructive Testing(NDT) of composites by various methods has become a hot research direction for researchers in recent years. Terahertz wave has low quantum energy and is transparent to most non-polar substances, so it has unique application advantages in the field of nondestructive testing of composites. In this paper, based on the characteristics of THz technology, the nondestructive testing of Terahertz Time-Domain Spectroscopy(THz-TDS) and terahertz imaging technology are discussed in detail, and the current development trends of terahertz nondestructive testing technology for composite materials are summarized. Finally, the development prospect is outlooked.

Abstract:Aiming at the UAV air-ground channel, based on the Space-Alternating Generalized Expectation-maximization(SAGE), the channel characteristic parameters are estimated with high precision, and the small-scale fading characteristics of the air-ground channel such as multipath delay and multipath power are extracted. Then, using uniform quantization and non-uniform quantization methods, the wireless channel key quantization is carried out on the main path power and the main path-multipath power difference of the measured data. The quantification efficiency, randomness, and algorithm running time of the key are analyzed for takeoff and cruise scenarios respectively, and compared with the key quantification results based on large-scale features. The key quantization efficiency results show that the non-uniform guard quantization is superior to the uniform guard quantization; the quantization method based on high-precision estimation of channel characteristics is better than traditional quantization based on large-scale features; and the quantization in the take-off scenario is better than that in the cruise scenario. The results of the performance test show that the keys obtained in these quantizations have good randomness; the running time difference of different quantization methods is small, therefore, the two quantization methods based on high-precision extraction bear low complicity.

Abstract:In some high dynamic weak signal scenarios, the carrier phase is difficult to lock. In order to track the high dynamic weak Global Navigation Satellite System(GNSS) signal, considering that the Frequency Locked Loop(FLL) is more robust than the Phase-Locked Loop(PLL), an algorithm based on FLL+differential demodulation is proposed to track and demodulate the GNSS signal. The algorithm uses the second-order FLL to track the frequency of satellite signal, and the differential demodulation algorithm is employed to demodulate bit data. In engineering application, the algorithm adopts the architecture of Field Programmable Gate Array+Digital Signal Processing(FPGA+DSP), realizes the pre-processing of signal tracking signal in FPGA, and realizes the tracking loop algorithm, bit synchronization and differential modulation in DSP. The simulation of the algorithm is performed in Matlab platform, and the algorithm is verified by receiving the real GNSS signal from the simulator platform and the sky. The simulation and experimental results show that the algorithm can realize the stable tracking of satellite signal and data demodulation under the condition of high dynamic and weak signal, and overcome the problem that the data cannot be demodulated due to the difficulty of PLL locking, finally realize the Position Velocity and Time(PVT) solution of GNSS signal under this condition.

Abstract:High range resolution of radar requires wideband transmitted signals, but the radar transmission of continuous wideband signal is limited by hardware cost and available spectrum resources. When multiple narrow-band signals are used for wideband aggregation, the range side-lobes will increase and the unambiguity range will decrease as the spectral discontinuity and step size of the narrowband signals increase. In order to solve the above problems, a new sparse frequency configuration is proposed, which can obtain equivalent continuous uniform stepped frequency signals through differential processing between sub-bands. Moreover, to make full use of the discontinuous sub-bands with large frequency span, the influence of frequency spans on target scattering characteristics is analyzed and a frequency consistency correction method based on Geometric Theory of Diffraction(GTD) model is proposed. The effects of different frequency spans on wideband aggregation are simulated and analyzed.The possibility of cross-band wideband aggregation is proved.The research of this paper can provide a reference for the backward compatibility of radar systems.

Abstract:With the opening of low-altitude airspace and the development of aviation technologies such as drones, the detection of low-altitude targets in areas with tight electromagnetic spectrum such as cities or suburbs has become more and more important. 5G based passive bistatic radar has a wide application prospect in this field. Compared with 4G network, the implementation details of 5G waveform scheme have undergone essential changes. Therefore, the ambiguity functions based on the signals of different external radiators are also quite different. Nevertheless, there is still lack of research on the ambiguity function of 5G signal. Based on basic structure of signal, the differences between 5G signal and 4G signal in frame structure and physical resource structure are analyzed in detail in theory. System simulation model is built, and the radar ambiguity function based on 5G signal is simulated. Finally, the cause of the ambiguity and the possible influence on the signal detection performance are analyzed, and the suppression methods of some side peaks are briefly explained. This work provides a new idea and direction for the suppression of side peaks of external radiator radar based on 5G signal.

Abstract:This paper introduces and analyses a novel dielectric base plate with an asymmetric shape and dielectric property aiming to achieve a uniform temperature distribution over the heating sample. Firstly, the proposed dielectric base contains FR-4(FR-4 Epoxy Glass Cloth) and alumine and is located within a commercial microwave oven to heat a potato sample. The permittivity and geometric values of the base are the selected parameters to be optimized for the sake of lowering the Coefficient Of Variation(COV) of temperature on the spherical medium heating sample and improving heating uniformity. Secondly, calculation of the multiphysical field simulation is applied to simulate the heating process. The simulation results based on COMSOL Multiphysics show that the COV decreases from 0.9134 to 0.5446 with the dielectric base. In other words, the COV declines by over 40%. Finally, an experimental system is built to measure the temperature of the heating sample to validate the simulations and calculations. Good agreements have achieved between the simulation and experiment, showing good consistence in temperature rise curves. It illustrates that the novel dielectric base can make the temperature uniformity of the heating sample improved.

Abstract:In order to make the high-frequency high-speed high-power transceiver component Transmitter and Receiver(T/R) work reliably and stably in complex electromagnetic environment, the design of component switching control, component power supply and ground, component layout and shielding are analyzed, the points of attention are suggested, and the design method is put forward. In the T/R component switching control design, the common mode interference problem is solved by a pair of delay and conjugate delay circuits to ensure that the transceiver time is longer than the driving switching time. The differential mode interference problem is solved by pulse width detection and maximum switching speed constraint. In the analysis of power supply and ground, the ground spacing is emphasized to not exceed one-twentieth of the signal wavelength. In the design of layout and shielding, the cavity resonance wavelength is analyzed in emphasis. Example modules are given and the above three design points are analyzed against each other to finally achieve stable and reliable operation in complex electromagnetic environments.

Abstract:The electromagnetic radiation prediction method of 5G base station is studied. A General Regression Neural Network(GRNN) model-based electromagnetic radiation environment representation method for base station is proposed, and the instantaneous broadband electric field strength at the ground plane of the theoretical maximum radiation point around the base station is predicted. 80% of the data is taken as the training set and 20% as the test set. Given the antenna transmission power, the distance between the 5G base station and its theoretical maximum radiant point, the data transmission time, the obtained Mean Absolute Percentage Error(MAPE) is 0.087 1, and the operating time is 3~5 min. The method shows good prediction accuracy and fast running speed. At the same time, by comparing with other models, the superiority of the method is verified, which is manifested in the substantial improvement of prediction accuracy and efficiency. With the increase of the prediction range around the base station, the advantages become more obvious, and the method has good applicability to different scenarios.

Abstract:Aiming at the problem of low resolution of millimeter wave human security inspection equipment using three-dimensional synthetic aperture imaging technology, a wavenumber domain IAA imaging algorithm is proposed by combining Iterative Adaptive Approach(IAA) technology and synthetic aperture imaging technology. IAA technique can estimate the energy of the signal source corresponding to each potential position, and bears the advantages of high resolution, low sidelobe and is suitable for single snapshot estimation. Through theoretical model analysis and simulation operation, the reconstructed rendering is compared with the traditional matching filter rendering to verify the effectiveness of the algorithm. At the same time, with the improvement of computing power, the performance of the algorithm will also be improved.

Abstract:It is difficult for traditional intrusion detection systems to obtain the relationship among network attack behaviors. Taking an attack graph representation model as a guide, an intelligent mining model of attack events based on Bayesian network is proposed. A Bayesian attack association graph is established based on prior knowledge. The network attack behaviors are aggregated based on attribute similarity. An efficient Ex-Apriori algorithm is designed for network attack scenarios to discover the association rules among the attack behaviors, and the attack behavior group set is established. Finally, the attack behavior group set is calculated by using the parameters of the Bayesian attack association graph to realize the discovery of attack events. Experiments show that this model can effectively extract network attack events and discover attack paths, and provide theoretical and technical support for the discovery and countermeasures of network attack events.

Abstract:A load detection model based on Event Driven and Deep Learning(EDDL) is proposed to address the issue of low detection accuracy in current non-invasive load detection. The current data is detected through zero crossing, and the key events are discovered from a large amount of data based on event driven mechanisms. The end-to-end non-invasive load detection is achieved by converting the current sequence containing key events into image space and incorporating it into a deep learning based load detection model. The experimental results show that compared with the Multi-class Support Vector Machine(MSVM), Feedforward Neural Network(FNN), Convolution Neural Network(CNN), and Long Short Term Memory (LSTM) models, the proposed EDDL model has better overall performance, with detection accuracy and accuracy of 94.67% and 91.76%, respectively. The simulation results verify that the proposed model can mine current data based on event driven mechanisms and effectively extract current data features based on deep learning models, thus achieving high-precision non-invasive power load detection. This model has certain reference value for the research of non-invasive power load detection.

Abstract:With the advent of the intelligent era, magnetic field sensors have been widely used in mobile devices to provide users with services such as positioning and navigation. At present, the magnetic field sensors based on Hall effect and the magnetoresistive magnetic field sensors which rely on magnetic materials are two dominant technologies in the market. The advantages of the magnetic field sensors based on the Hall effect include low cost, no need for magnetic materials and fabrication compatibility with the Complementary Metal Oxide Semiconductor(CMOS) technology. The operating range of this kind of sensors typically is from 10 μT to 1 T, and the resolution can be improved by increasing the power consumption. Magnetoresistive magnetic field sensors have high resolution and wide operating range(0.1 nT~1 T), and their performances mainly depend on the magnetic materials adopted. Besides these two technologies, resonant magnetic field sensors composed of silicon-based Micro-Electro-Mechanical System(MEMS) resonators have received extensive attention in recent years due to their benefits of small form factor, low power consumption, high performance and fabrication compatibility with CMOS technology. This paper reviews the latest developments of magnetic field sensors using silicon-based MEMS resonators. In addition, methods for improving the performance of such sensors are described. The current key challenges and future opportunities are provided.

Abstract:During the period that the Photoconductive Semiconductor Switches(PCSS) is operating at a high repetition frequency, it generates filament current heating, then the temperature of the PCSS quickly exceeds the maximum operating temperature, causing the PCSS to fail or damage. Combining the advantages of microchannel heat sink and jet cooling technology, a high-efficiency micro-channel/jet impingement heat sink is designed. Through experimental tests, the heat transfer characteristics of the micro-channel/jet impingement heat sink under different operating conditions are studied, and the heat dissipation performance is compared with that of the honeycomb micro-channel heat sink imported from the United States. The experimental results show that when the volume flow rate is 3 L/min, the heat transfer coefficient of the micro-channel/jet impingement heat sink exceeds 35 000 W/(K·m²), and the heat dissipation is as high as 1 000 W, which is higher than that of the honeycomb microchannel heat sink by 45%. Under the test flow rate, with the increase of the volume flow rate, the average heat transfer coefficient of the micro-channel/jet impingement heat sink approaches a linear increase. The average heat transfer coefficient of the honeycomb micro-channel radiator increases slowly at large flow rates. In addition, compared with the method that cooled by the honeycomb microchannel heat sink, the uniformity of the heat source temperature cooled by the micro-channel/jet impingement heat sink is significantly better, and it can reduce the temperature fluctuation of the heat source surface by 58%,which is more conducive to reduce the thermal stress of the PCSS.