Abstract:Being different from traditional terahertz components, silicon-based terahertz systems have the characteristics of low cost, small size, high integration, great maneuverability, and easier implementation of large arrays for large volume adoption. In the past ten years, with the rapid development of semiconductor technology and the increase of the cut-off frequency of silicon-based process transistors, the field of silicon-based terahertz system chip design has developed rapidly. The current research status and development trends of silicon-based terahertz system chips from four aspects: silicon-based terahertz sources, silicon-based terahertz imaging chips, silicon-based terahertz communication chips, and silicon-based terahertz radar chips are reviewed in this paper.

Abstract:Terahertz waves with unique spectrum characteristics have provided important applications in cross frontier fields of astronomical observation, interstellar communication and defense security. As one of the key components in the terahertz detection/communication systems, the filter can extract characteristic signals and suppress interference frequencies to improve the target detection performance of the system. In recent years, thanks to the development of the high-precision manufacturing process, some breakthrough results have been achieved in terahertz waveguide filters. And the filters based on different types, structures and processes have been studied. In this review paper, the development status and common problems of terahertz waveguide filters are expounded based on the different processes. The advantages and disadvantages of filters developed by mainstream technologies are also summarized, which can provide a reference for the further development of terahertz waveguide filters with high performance.

Abstract:Terahertz(THz) imaging has shown wide application prospects in many fields such as human body security inspection, non-destructive inspection, quality monitoring, biomedicine, and semiconductor characterization. In this article, various two-dimensional THz imaging techniques are reviewed, including scanning imaging, single-pixel imaging, electro-optic modulation imaging, direct imaging with THz camera, and so on. The research backgrounds of various imaging technologies are summarized, the specific imaging methods and imaging results are analyzed. The advantages and disadvantages of different terahertz imaging technologies are concluded, and the future development trends of terahertz imaging technologies are forecasted.

Abstract:Because terahertz(THz) waves have the characteristics of low energy, strong penetration, and broad bandwidth, terahertz imaging technology has been widely used in many fields such as non-destructive testing, biomedicine, and safety testing. How to improve the resolution of terahertz imaging in practical applications is becoming more and more important. Terahertz near-field imaging technology can break through the diffraction limit and obtain high-quality images with submicron or even nanometer resolution, thus high-resolution THz imaging technologies based on near-field methods have been proposed and further applied. This article first describes the basic principles of terahertz near-field imaging; secondly, summarizes its progresses and enhancement methods; and finally prospect the future of terahertz near-field imaging.

Abstract:Terahertz time-domain spectroscopy is used as a new spectroscopic detection tool for the characterization of a wide range of substances including hydrates. Metal sulphates have a variety of different hydrates that exhibit different absorption properties in the terahertz band, and the different hydrates of transition metal sulphates can be effectively characterized by using terahertz spectroscopy. In this paper, magnesium sulphate and its hydrates were characterized by using a terahertz time-domain spectroscopy system. Different magnesium sulphate pyrolysis products were obtained by constant temperature drying of magnesium sulphate heptahydrate and their terahertz absorption spectra were investigated, which shows that different hydrates exhibit significantly different terahertz absorption properties. The research provides a simple, fast and effective means of characterization for the detection of magnesium sulphate and its hydrates, as well as an important reference for a variety of applications of magnesium sulphate.

Abstract:It is difficult to excite large chiral optical responses for metasurfaces based on single-layer metal resonators under normal incidence, because they are difficult to excite in-plane magnetic dipole moment that are not orthogonal to the electric dipole moment. The displacement current excited by optical field in the dielectric meta-atoms may induce an in-plane magnetic moment to achieve chiral optical responses. A huge chiral response is achieved in terahertz band based on the lossless all-silicon metasurface. The leaky waveguide mode in the chiral silicon pillar excites the in-plane magnetic dipole moment, which triggers the spin-selected backward electromagnetic radiation, and then realizes the chiral optical response of terahertz wave. A polarization-dependent TDS system is built by using wire grid polarizers，and the peak value of circular dichroism in the transmission spectrum reaches 0.2. This simple-prepared all-silicon metasurface provides a new idea for the design of terahertz chiral metadevices, and it is expected to be applied in the fields of terahertz imaging and spectral detection.

Abstract:In radio astronomy field, the development of terahertz superconducting coherent receivers with ultra-wideband performance is required to achieve the simultaneous observation of multi-spectral lines in much wider frequency band. In response to the application requirements of the next-generation terahertz ultra-wideband receivers, an ultra-wideband ridge waveguide duplexer with a frequency band covering 180-420 GHz (the fractional bandwidth up to 87%) is developed. The main contents include the design and conversion of broadband ridge waveguide filters in 180-300 GHz and 320-420 GHz band, as well as the optimization of terahertz multi-stage coupled ridge waveguide duplexer. The simulation results show that this structure can be in duplex operation in the 180-300 GHz and 320-420 GHz bands with an overall return loss better than 15 dB and the isolation more than 20 dB.

Abstract:A multi-channel terahertz waveguide filter based on multimode resonance is studied. By introducing defects in terahertz periodic structure waveguide, the passband can be formed in the forbidden band range, so as to realize narrow-band filtering. The characteristics of multi-channel filter are studied by numerical simulation. The results show that the multi-channel filtering function with adjustable number of channels can be realized by changing the defect length. The number of channels can reach 10-12, and the transmittance is more than 98%. In addition, by changing the number of cycles of the waveguide structure, the passband bandwidth can be adjusted, and the narrowest bandwidth can reach 0.01 GHz. The waveguide filter has excellent performance and has the advantages of compact structure, easy integration, high transmittance, multi-channel and narrow bandwidth. It provides an important technical reference for the development of functional devices in terahertz band.

Abstract:The terahertz polarization manipulation technology based on electromagnetic metasurface is studied. Specifically, a reflective-type terahertz 90o linear polarization converter is designed by using the metal-dielectric-metal sandwiched structure, and the polarization conversion characteristics are investigated both numerically and experimentally. It is shown that the reflective-type metasurface designed in this work achieves a high polarization conversion efficiency(above 75%) at the operating frequency of 0.5 THz as well as a broad working band(the polarization conversion efficiency is more than 50% over the frequency range of 0.35-0.65 THz). In addition, the ultrathin glass substrate produces the excellent overall performances of the metasurface linear polarization converter, including small thickness, light weight, and good heat resistance.

Abstract:Saccharides are typical chiral substances, and their chiral spectra in the terahertz band have not been fully studied. The refractive index and absorption spectra of lactose, galactose, and glucose at low temperature and normal temperature are studied respectively, and the chiral spectra of these samples are obtained through terahertz time-domain polarization spectroscopy. The experimental results show that the absorption of saccharides will decrease as the temperature decreases, which is conducive to obtain the chiral characteristics of the sample at low temperature. At 80 K, glucose exhibits strong Circular Dichroism(CD) in 1.3-1.5 THz; the CD peak value reaches 44.97% at 1.39 THz. All three saccharides have specific chiral characteristic peaks, and the CD values all exceed 20% in 1.6-1.8 THz. The research results can provide important reference for further understanding of the chiral spectra of chiral biochemical samples in terahertz band and their internal mechanisms.

Abstract:A negative tapered-double-sinusoidal grooves structure is proposed in order to form a coaxial Bragg reflector with narrow bandwidth, high quality factor Q and good selectivity. According to the coupling mode theory, on the basis of the ordinary sinusoidal groove structure, the auxiliary sinusoidal distribution with smaller etching period is superimposed, and the negative taper is added on the inner and outer walls of the conductor to form the negative tapered-double-sinusoidal grooves coaxial Bragg structure. Through FORTRAN software programming, compared with that of the ordinary sinusoidal grooves, the bandwidth of the working mode and the competing mode of the negative tapered-double-sinusoidal grooves coaxial Bragg structure gets narrower, the quality factor Q gets greater, and the residual side lobe phenomenon is suppressed. At the same time, the center resonant frequency point of the competition mode is far away from that of the working mode, the band gap overlap is further separated, and the frequency selectivity is improved. The structure design is simple and reasonable, which can better separate the working mode and the competition mode, and is favorable to construct a single high-order mode resonator with high quality factor Q and high power.

Abstract:Low-Density Parity-Check code(LDPC) decoding is one of the key steps in reference signal reconstruction of passive radar. Decoding algorithms can improve data bit errors caused by noise, but with the high complexity. Combining high memory throughput and tremendous computational horsepower of GPU graphics processor, this paper proposes three types of parallel LDPC decoding algorithms suitable for GPU processing based on hard, mixed, and soft decisions. The complexity, decoding performance, and impact on radar signal processing of the three types of algorithms are described; finally, a parallel GPU implementation scheme is given, and the real-time time-consuming of the algorithms is compared. The simulation and measured results verify that the soft decision parallel algorithm is superior to other algorithms on performance and effectiveness.

Abstract:When Global Navigation Satellite System(GNSS) receivers move in high dynamic environment, the Directions Of Arrival(DOAs) corresponding to interferences may change rapidly, which will reduce the performance of anti-jamming algorithm. A novel null widening algorithm based on signal power estimation is proposed. Firstly, according to the eigenvalues, the Sampling Covariance Matrix(SCM) is divided into signal subspace and noise subspace, and a set of linear equations is established based the signal subspace projection. Then, the signal powers around interferences are reset according to the required null width based on the linear equations. Finally, the Interference-plus-Noise Covariance(INC) matrix can be reconstructed with the reset signal power, based on which the weight vector is solved. Simulation shows that the proposed algorithm has a deeper null than other algorithms when the null width keeps the same, and the Signal to Interference Noise Ratio(SINR) of array output is also improved.

Abstract:A Double Data Rate(DDR) Synchronous Dynamic Random Access Memory(SDRAM) combined with Quad Data Rate(QDR) Static Random Access Memory(SRAM) storage system is proposed to overcome the problem of huge amount of SAR imaging echo data. An in-place transposed storage method is designed for the system to improve the memory resource utilization. This method compares the length of the range and the azimuth of radar echo data firstly. It reserves some free space of the memory to improve the flexibility of the logical mapping of the read address and the write address of memory. The free space is the same as the storage space occupied by a single row or column of longer data in the range direction and the azimuth direction. It effectively realizes the on-chip transposition operation of a large amount of data, and saves the utilization amount of DDR. And the sub-block matrix address mapping method and cross-BANK address mapping method are applied to the in-place transposition, which effectively improves the access to the SAR echo data transposition. The experimental results show that the data storage system reduces the amount of DDR memory by half while meeting the real-time imaging requirement, improves the resource utilization of DDR, and cuts the cost. At present, it has been successfully applied to SAR imaging processing in multiple modes.

Abstract:Increasing the coherent accumulation time is an effective method to improve radar detection capability. However, when target velocity is high, long-time coherent accumulation will lead to the range migration effect of the target, reduce the Signal-to-Noise Ratio, and affect the radar's detection power. Aiming at the range migration problem, Keystone Transform(KT) correction algorithm is given. The performance of three KT implementation methods are simulated and evaluated. Then, a parallel implementation algorithm based on Chirp Z Transform(CZT) on the Graphics Processing Unit(GPU) is proposed and implemented. Experimental results verify the real-time performance and effectiveness of the proposed method in combination with the passive radar system.

Abstract:An adaptive method based on wavelet packet transform and TRansform domain Least Mean Square(TRLMS) is proposed in order to solve the problem that the pulse interference near the service frequency band of aeronautical radio navigation affects the receiver, and further improve the ability of pulse interference suppression in the Global Navigation Satellite System(GNSS). By using the best wavelet function decomposition to track the frequency band of the positioning pulse interference, and adopting TRLMS adaptive filtering instead of the conventional fixed threshold method of wavelet packet, the interference is suppressed. The simulation results show that the mean square error of the proposed method is smaller than that of other methods. It solves the problem of useful signal loss and has better interference suppression performance.

Abstract:Position finding system with azimuth and time difference is commonly applied in electronic reconnaissance filed. In long-distance geo-location, a poor positioning accuracy would be caused by inaccurate earth model. An algorithm for azimuth and time difference joint positioning is proposed. In this method, a theoretical model of two-station azimuth and time difference joint positioning is established, and a rough analytical solution is obtained by solving the spherical triangle combining the spherical model of the earth. Then, the azimuth observation equation in the spherical coordinate system is converted into a plane equation. The earth ellipsoid model time difference measurement equation under the geocentric rectangular coordinate system is introduced. Starting from the rough solution, the exact solution is obtained based on Newton iteration method. Finally, the effectiveness of the model is verified by experimental simulation. The proposed method solving positioning finding of azimuth and time difference in long distance provides a technical reference for engineering implementation.

Abstract:Aiming at the dynamic target tracking problem in Wireless Sensor Networks(WSN) with limited sensing range, a collaborative dynamic target tracking algorithm in which Kalman Consensus Filter(KCF) is combined with dynamic clustering self-organization is proposed. The proposed algorithm uses a dynamic clustering protocol which consists of a cluster leader selection phase and cluster reconfiguration phase to limit messages exchanges between nodes participating in the target state estimation process. Then, a distributedly weighted estimation-prediction algorithm, namely Calman consensus filtering can be adopted to estimate the target state and predict its next position. This helps waking-up the most appropriate nodes to track the target and well organizing the network communications, while other nodes remaining in sleep state. The simulation results show that the proposed algorithm can not only reduce the average energy consumption of the network, but also improve the error estimation quality in the tracking process significantly compared with a centralized algorithm and other two kinds of distributed dynamic target tracking algorithms in common use.

Abstract:A tracking scheme based on Probability Hypothetical Density(PHD) filtering is proposed in order to realize the 3D target positions tracking. The scheme consists of two phases, namely single view tracking phase and multi-camera fusion phase. In the former, at each camera at time k, the color observations are obtained and then the Gaussian Mixture Probability Hypothesis Density(GMPHD) filter is utilized to estimate the 2D target locations.In the latter, the set of 2D estimations of targets, which is obtained in the former, is considered as observations for the data fusion phase to estimate the 3D target locations by the GMPHD filter, so as to avoid the data association between observations and states of targets. The experimental results show that the proposed tracking scheme can not only reliably track the 3D target positions,but also handle the shielding problem for targets at each camera.

Abstract:In high speed maglev vehicle millimeter-wave communication systems, it is required that the vehicle antenna has the characteristics of miniaturization, wide band, circular polarization and radiating sector beam. To better meet these requirements, a compact waveguide spiral array antenna with center feed is proposed. The antenna feed system adopts the form of coaxial waveguide central feed and four rectangular waveguides joint feed. By changing the size of the feed waveguide, coupling the length of the probe and placing the coaxial converter at the tail of the feed waveguide, the uniform feed of each unit is realized; the antenna low-profile unit is constituted by the helical antenna, and the circular polarization performance of the antenna is improved by using sequential rotation technique. A 28-element waveguide spiral array antenna with a center frequency of 38 GHz is designed by using full-wave electromagnetic simulation software and tested experimentally. Test results show that: in 37-39 GHz band, the antenna standing wave ratio is less than 1.41, the gain above 21.7 dB, the axial ratio less than 3.6 dB, the beam width 4.5°-4.7° at the elevation plane and 29°-29.7° at the azimuth plane. It can meet the design requirements of the vehicle antenna for millimeter wave vehicle-ground communication system.

Abstract:The development of electromagnetic two-dimensionally reconfigurable filter is reviewed. The background, significance, development status and regulation principle of electromagnetic two-dimensionally reconfigurable filter are introduced. The electromagnetic two-dimensionally reconfigurable filter is divided into two types: magnetoelectric composite structure and magnetoelectric adjustable hybrid structure. The performance analysis of these two structures is carried out respectively. The performance parameters of the electromagnetic two-dimensionally reconfigurable filter with different magnetoelectric composite structures and different materials are compared. Finally the existing problems and future development trends are discussed.

Abstract:A structural compact wideband low sidelobe antenna array operating at X and Ku bands is designed for meeting the requirements of the electronic systems. The antenna array could achieve the relative bandwidth of 54.5% and the sidelobe level below -30 dB with the longitudinal dimension of 4.5λg. The array consists of 48 dipole elements and a stripline weighted power divider. To extend the bandwidth of the dipole element, a short-circuited probe at the end of the feeding stripline is employed to compensate distribution capacitive effect. A parasitic patch over the dipole is utilized to improve the radiation performance. To reduce longitudinal dimension of the array, the layout of the power divider is optimized according to the optimal power ratio of each node from the topology design. The experimentally validation is conducted in the near-field microwave anechoic chamber.

Abstract:As the integration and complexity of Monolithic Microwave Integrated Circuit(MMIC) increase, the distance among the chip functional modules is getting closer and closer, and the characteristic line width is getting narrower and narrower. For analyzing the signal path and signal integrity inside the chip, it is particularly important to provide high-resolution microwave field imaging of the chip surface. In order to solve the problem of accurately detecting the integrity of the internal structure of the chip, this work uses a fiber based near-field scanning probe method, in which the diamond particle containing the nitrogen vacancy(NV) center is fixed at the tip of the fiber by building the optical path and receiving the fluorescence signal of the diamond NV center, so as to infer the magnetic field strength of the chip under test. In this experiment, an area inside a microwave low-noise amplifier chip is selected for scanning imaging, good imaging results are obtained, and the signal line trend of the chip is accurately analyzed. These results provide a transformative method for the function and failure analysis of integrated devices such as highly integrated chips and filters. It has achieved good test results in application fields such as chip electromagnetic compatibility, integrated antenna near-field characterization and digital circuit signal integrity analysis.

Abstract:Aiming at the image segmentation problem in ship Synthetic Aperture Radar(SAR) image recognition, the method of mathematical statistics is utilized to study the ship SAR image. After analyzing classical K–Means clustering algorithm and Gaussian Mixture Model(GMM), an improved Gaussian mixture model is proposed to segment ship synthetic aperture radar images. The method adopts the Mahalanobis distance to improve classical K–Means method. At the same time, each probability distribution of traditional GMM is further subdivided into individual probability components. In the calculation of auxiliary variables, a gradient ascent algorithm is applied. The experimental results show that the segmentation results obtained by this study are more accurate and more stable than the segmentation method using the classic K–Means algorithm and ordinary Gaussian mixture model.

Abstract:The Weighted K Nearest Neighbors(WKNN) algorithm based on the off-line Received Signal Strength Indication(RSSI) fingerprint database has been studied intensively in the indoor positioning methods based on the received Wireless Fidelity(WiFi) signal. However, the specifications of the received RSSI fingerprint data, such as the high dimension and many invalid default RSSI values, have not been addressed in the existing WKNN algorithm, which is not good for improving its positioning accuracy. Aiming at the problems of the existing WKNN algorithm, the received RSSI values will be sorted in descending order, and the RSSI values larger than the preset threshold are selected to match with the off-line RSSI fingerprint database in the following steps. Then, the K value is determined on line adaptively by the statistics of the Euclidean distances. Finally, the Gaussian weights are updated by the means of the Euclidean distances. The experiment results show that the improved WKNN algorithm achieves more accurate positioning performance than the existing WKNN one.

Abstract:A Weibull-Weibull(WW) distribution modeling method and its statistical characteristics are studied in order to better describe the heavy tailing phenomenon that occurs in the modeling of X-band sea clutter with low grazing angles. The fitting effect of the statistical distribution model on sea clutter data is improved. Based on the measured data of X-band sea clutter, the fitting effect of WW distribution on measured sea clutter data under different sea conditions and polarizations is analyzed. The comparison with the goodness-of-fit test of statistical distribution models such as Weibull distribution, Lognormal distribution, and K distribution shows that the WW distribution can well fit sea clutter data with heavy tailing. In addition, the WW distribution can accurately describe the statistical characteristics of sea clutter in different polarization domains, and has strong statistical modeling ability for sea clutter amplitude distribution.

Abstract:The detection and track of specified moving small object is an important subject in Computer Vision. By changing the position of the feature maps for fusion in the YOLOv3, building the custom database including three classes, and completing the combination of classes by using Intersection Over Union(IOU), a detector is created, which is able to detect the specified moving small object and makes mAP@75 reach 47.41 in the test customer's data set. Combining Kalman Filter and Hungarian method, and putting the scale information of predicted bounding box and ground bounding box, the detector can track the object and reduce the ID switch caused by camera's fast movement. The whole system's speed reaches up to 0.109 7 s/frame using one NVIDIA GeForce GTX 1060 6GB GPU.

Abstract:Slot assignment is the core component of Time Division Multiple Access(TDMA) protocols in wireless networks. By dividing the time into several fixed time slots, TMDA enables the two interfering nodes to transmit data in different time slots, thereby reducing the access collision rate. Therefore, a distributed TDMA slot allocation algorithm is proposed in this paper. Based on the Drand algorithm, the proposed algorithm is improved. Routing information is utilized to allocate time slots to reduce communication delay and the number of transmitted messages. The experiment results show better performance in comparison to referenced distributed channel allocation approaches. The latency is improved by 8%, and the messages complexity is reduced by 24% respectively.

Abstract:It is challenging to build networking protocols for Underwater Sensor Networks(UWSNs) due to specific characteristics of UWSNs, such as high latency, low bandwidth, and high energy consumption. Therefore, Topology-Aware Routing(TAR) in Underwater Sensor Networks is proposed. TAR routing first makes each node obtain the network topology information through the interactive Beacon package, and establishes the neighbor information table. Then, based on the residual energy of the node and the reliability of the link, the next-hop forwarding node is selected to improve the stability of the route and balance the energy consumption among nodes. Simulation results show that the proposed TAR route enhances the routing stability and reduces the energy consumption of nodes.

Abstract:A method for modeling receiver behavior based on polynomials is presented. First, a Hammerstein model structure is employed to build a receiver behavior model, and nonlinear module and memory linear module are utilized to characterize receiver nonlinearity and memory effects, respectively. Secondly, the nonlinear module parameters and the linear module parameters of the behavior model are identified by using the Fourier series and the least square method. Finally, the receiver nonlinear behavior modeling method is verified by simulation data of the receiver ADS model. The AM-AM characteristics and signal-tone time-domain waveforms of the ADS simulation and behavior model are compared and analyzed. The experimental results show that the AM-AM characteristic curve and the time-domain waveform of the receiver behavior model agree well with the ADS simulation data. The proposed method can predict the receiver's nonlinear response, and shows theoretical value for evaluating receiver nonlinear effects in complex electromagnetic environments.

Abstract:Aiming at the problems of conventional Radio Frequency Identification(RFID) positioning process, Differential Evolution(DE) algorithm is proposed to optimize the positioning accuracy of RFID. This method first randomly initializes reference tag location coordinates, calculates the distance between reader and tag by using Received Signal Strength(RSS) value. Then it estimates the location coordinates of the nearest label under test by optimizing the reader and the distance error between the reference labels and tags under test. Finally, it is compared with classical LANDMARC positioning systems. The simulation results show that the average positioning error of the classical LANDMARC positioning system is 1.115 8 m, and that of the system optimized by DE algorithm is 0.001 2 m, which proves that the method of RFID positioning optimized by DE algorithm is effective.