Abstract:Terahertz(THz) optoelectronics has promoted the development of the THz generation, transparent control, and detection methods，and hastened many devices in the past decades. Especially, THz metamaterials and metasurfaces will exhibit extraordinary electromagnetic response when the subwavelength scale metal structure is excited by the THz illumination. Therefore, they have been applied to the devices such as wave beam shaper, waveguide, and modulator etc. The THz metamaterials and metasurfaces also show the potential applications in the research fields such as sensors, communications, and radars. In this paper, the works about the spectrum and wavefront modulation with THz metadevices carried out in our group are summarized. The basic theory and corresponding experiment results for different devices are introduced. It is expected these works can pave the avenue of the application of the THz metadevices.

Abstract:Traveling Wave Tube(TWT) bears high gain, wide bandwidth and large output power. However, the output power will decline significantly when the operation frequency rises to Terahertz range. In order to increase the output power of THz TWT by parallel multi-beam and power combination method, theoretical analysis and numerical simulation of parallel multi-beam D band Folded Waveguide-TWT(FW- TWT) are performed. The simulation results demonstrate that the method can achieve the power combining output of multi-amplified signals. According to the simulation, single-beam mode behaves flat dispersion characteristics between 0.135 THz and 0.157 THz; the 3 dB gain band is 13 GHz(0.135 THz-0.147 THz) and the largest gain is 20.88 dB at 0.14 THz; multi-beam mode gets 20.8 dB combining gain at 0.14 GHz and the combining efficiency is not below 92% in 3 dB gain frequency range. The structure is fabricated by micro milling with a dimension error below the designed values. The transmission characteristics of D band Two Beams Folded Waveguide Structure(TBFWS) are simulated and tested. The study shows important meaning for achieving high power THz radiation based on nowadays heat cathode level.

Abstract:Terahertz-wave Parametric Oscillator(TPO) based on phonon-polariton scattering is one of the promising methods for obtaining high-energy and coherent THz-wave. A high-energy THz-wave output has been experimentally demonstrated with terahertz-wave parametric oscillator based on surface-emitted configuration. The maximum THz-wave output energy of 634 nJ/pulse is obtained at 1.63 THz. The rapid tuning is achieved by rotating the injection angle of pump beam into MgO:LN crystal using an optical beam scanner. The wide tunable range is from 0.75 THz to 2.81 THz. It is excepted that such high-energy THz-wave source can meet the demands in many applications, including biomedicine, communication and environmental monitoring.

Abstract:The single shot measurement of terahertz pulse is of great importance to the study of terahertz spectrum on ultra fast irreversible or single shot processes. A femtosecond pulse with tilted intensity front generated by using commercial grating are adopted as the probe beam for the measurement, in order to implement single shot measurement of terahertz pulses with low distortion and high frequency resolution. The time window is up to 20 ps and spectrum range covers from 0.1 THz to 2.5 THz. The result agrees well with that of the traditional electrical-optic sampling method. Analytical model for the single shot measurement of terahertz pulse using tilted pulse front technique is established, and some conclusions concerning the parameters preference of grating and optical system components, as well as optical design, are obtained.

Abstract:A detector can achieve quick response when it is much smaller than the wavelength of the source signal in THz wave band at the expense of signal coupling capability．Therefore, an antenna is applied to collect signals in order to enhance the signal coupling capability of the detector．The properties of antenna determine the frequency response band，the sensitivity and other parameters of the detector directly. A planar-integrated antenna is adopted for signal acquisition in the Nb5N6 microbolometer detector, which is fabricated by lithography，lift-off and other processes of micro-fabrication. The Nb5N6 microbolometer is placed in the center of the planar antenna. Aiming for the center frequency of 0.32 THz, a special capacitive coupling design is proposed to improve the signal coupling capability．

Abstract:The background requirements of the fuze antenna in terahertz spectrum as well as its advantages and disadvantages are introduced. The working principles and application characteristics of dielectric lens antenna in terahertz frequency are analyzed in order to implement the terahertz fuze antenna. The longitudinal size of H plane horn antenna can be reduced effectively by using fuze antenna formed by an H plane horn with dielectric lens antenna. The terahertz fuze antenna with different beam angles is achieved by focal technology of lens. The feasibility of the technology solution is verified through simulation.

Abstract:A double gate setting with priority of Doppler velocity and the Extended Kalman Filter(EKF) based Multiple Hypothesis Tracking(MHT) algorithm are proposed in order to realize Multiple Targets Tracking(MTT) in High Frequency(HF) ground-wave radar, and to effectively improve the performance of MTT by using the Doppler measurement. In the EKF based MHT, parameters obtained in the EKF are adopted directly to calculate the probability of each hypothesis. A simulation scene is built, and the EKF based MHT algorithm is compared with the one which assumes that the Doppler measurement is independent from the radius measurement. Simulation results show that the double gate setting helps induce number of clutter, and the EKF-based MHT algorithm is better than the other one under dense environments of HF ground-wave radar with stronger track-catching and false-alarm-filtering ability and higher efficiency.

Abstract:Spotlight mode is a special mode of Synthetic Aperture Radar(SAR), which can achieve higher resolution image than the ordinary strip-mode SAR. Starting from the top-level parameters design of high resolution space-borne spotlight SAR system, combining with the detailed analysis of system design and simulation process, many influence factors including long migration distance, Pulse Repetition Frequency(PRF), antenna pattern on spotlight SAR system design are analyzed. This work can provide a reference for space-borne spotlight SAR top-level parameters design.

Abstract:Priority Queueing(PQ) guarantees that traffics with higher priorities get higher Quality of Service(QoS), whereas the performances of those with lower priorities are poor, therefore reducing the total performances and fairness. A scheduling algorithm is proposed combining Priority and bandwidth Requirement Queueing(PRQ), which adopts bandwidth requirement to modulate scheduling probabilities on the base of priority scheduling, aiming to increases the scheduling probabilities of traffics with lower priorities, to improve their QoS and the total performances, and to receive better fairness as well. The simulation results show that PRQ significantly improves the QoS of traffics with lower priorities and the total performances, beating PQ on fairness.

Abstract:The transmission Bit Error Rate(BER) of Multiple-Input-Multiple-Output Differential Chaos Shift Keying(MIMO-DCSK) communication systems under Rayleigh fading channels are analyzed. Gaussian Approximation(GA) method based on the Central Limit Theory(CLT) is presented. The simulation results show that the consistency between GA BER curves and actual simulated curves enhances with an increasing spreading factor. Compared with DCSK, the BER performance of MIMO-DCSK is greatly improved by the increasing number of transmitting and receiving antennas. And the increase of the number of receiving antennas can get more gain than increasing transmitting antennas. With the increase of transmitting antennas, the non-orthogonality of the signals among different antennas leads to a deviation between GA BER curves and simulation curves, which will reduce after the spreading factor increasing.

Abstract:Opportunistic spectrum access for a single secondary user under periodic sensing framework is analyzed aiming for the unslotted primary user network. By constructing the secondary user channel sense and access model, an opportunistic spectrum access algorithm based on user request data packet length is proposed. The proposed algorithm could automatically modify the strategy of opportunistic spectrum access according to the service data packet length allocated by each slot. Experiment results show that the proposed algorithm can enhance the secondary users expect effective throughput under the condition of tight interference, and realize the tradeoff between effective throughput and collision probability. It behaves strong robustness against the exotic environment changes.

Abstract:Interference Alignment(IA) technology shows a great potential to improve the capacity of future wireless network immensely, and it becomes a research focus in interference elimination field. Nevertheless, among the existing distributed algorithms like Minimum Interference Leakage(MIL), maximum-SINR (max-SINR) and Minimum Mean Square Error(MMSE), there is no such an optimal solution that could outperform the others throughout the SNR values. Based on a diversity analysis on existing standards, an adaptive selection mechanism is proposed, helping both transmission parties choose the optimal algorithm according to the communication condition. The simulation results show that compared with mono-algorithm, the newly proposed selection scheme can achieve as much as 5 dB SNR gain when the same data rate is obtained.

Abstract:High Peak to Average Power Ratio(PAPR) is one of the major disadvantages of the Visible Light Communication(VLC) Orthogonal Frequency Division Multiplexing(OFDM) system as it can cause signal distortion. A Selective Mapping(SLM) method is introduced in order to reduce the PAPR of OFDM signal in VLC system, which is modified to suit the demand that the signals must be positive and real. A method combining the Discrete-Fourier-Transform Spread(DFTS) and SLM is proposed to reduce the PAPR in VLC OFDM system further. The simulation results show that，comparing with the original signal，DFTS or SLM method used alone, the DFT-S-SLM method has the best PAPR performance at the cost of a certain increase of system complexity.

Abstract:Ultra-wideband(UWB) communication shows its advantages of fast data transfer(100 Mb/s or above) in a relatively short distance(typically below 10 m) with relatively weak power consumption (energy spectrum below -41.3 dBm/MHz). Integrated with Multiple Input Multiple Output(MIMO) technology, channel capacity could be further enhanced. As a critical link in the ultrawideband communication，UWB antenna needs extra efforts in design optimization to boost the performance of the whole system. UWB antenna is defined as the antenna whose bandwidth exceeds 500 MHz or relative bandwidth greater than 20%. This paper takes the most representative Vivaldi antenna as a show case for multi-objective optimization design with statistical methods. The optimized miniaturized antenna(sized130 mm×100 mm) shows a -10 dB bandwidth of 2.4 GHz. The design method provides guidance in common wideband，multi-parameter antenna design.

Abstract:A Ku-band backward wave oscillator with low magnetic field is designed in order to realize the High Power Microwave(HPM) system miniaturization, according to the basic theory of traditional Relativistic Backward-Wave Oscillator(RBWO) with low magnetic field. The effects of beam voltage, beam current and the guiding magnetic field on the output power are analyzed. The structure is optimized by using particle simulation(PIC). A microwaves output power of 1.0 GW with the frequency of 13.1 GHz is obtained under the guiding magnetic field of 0.4 T, the diode voltage of 600 kV and the beam current of 7 kA. The preliminary experiment is performed at low magnetic field condition. Under a guiding magnetic field of 0.4 T, the microwave power of 850 MW with 13.05 GHz frequency and 24 ns pulse width is obtained. The experiment has laid a good foundation to realize the GW microwave output with lower magnetic field.

Abstract:The ridge-loaded coaxial radial line slow wave structure is presented in this paper. The dispersion characteristic and coupling impedance of this slow wave structure are investigated by electromagnetic simulator High Frequency Structure Simulator(HFSS). It is analyzed that the change of structure parameter affects the high-frequency characteristics. The results show that the inner conductor radius and the period length have obvious effect on phase velocity. Along with the decrease of inner conductor radius and period length, the phase velocity and operating voltage can be favorably decreased. In addition, the width of the ridge makes the coupling impedance increase, when this structure is used as the slow wave structure, the gain and efficiency of the traveling wave tube can be improved. Meanwhile the length of ridge has no obvious effect on the high-frequency characteristics. Because the ridge-loaded coaxial radial line slow wave structure is a new all-metal structure with the advantage of broad bandwidth, high power capability and lower losses, it has a large potential of application in millimeter traveling-wave tubes.

Abstract:The electromagnetic radiation of high voltage power transmission equipment mainly includes the constant-frequency electromagnetic radiation，electrical noise and corona radiation interference，which can change the electromagnetic environment around. The analytical expressions of electromagnetic environment are derived for the high-voltage transmission lines and substation. And the scattering interference and shielding effect are analyzed. A test method is designed to measure the impact on wireless communication signals. The test results show that high-voltage power transmission equipment may cause interference scattering, which makes radio propagation multi-path effect more significant，thus affecting the strength of remote reception field.

Abstract:A VANET-CELLULAR integrated network architecture is proposed to ensure efficient data exchanging for various applications in Vehicular Ad-hoc NETwork(VANETs). In this architecture, vehicles are dynamically clustered by related metrics, and those vehicles conformed to the context-aware requirement are selected as mobile gateway to link the 3GPP networks. A distributed game theoretic approach is adopted to stimulate vehicles to cooperate with their neighbors, and the overall performance of communication is improved by evolutionarily maximizing each vehicle’s own utility. The simulation results show that this approach works efficiently in selection of the minimal mobile gateways in VANETs.

Abstract:As a kind of Finite Impulse Response(FIR) filters, pulse shaping FIR filter is implemented by Multiply-Accumulates(MACs), which performs convolution between input signal and unit pulse respond. Nevertheless, the convolution will cost a lot of MACs as the coefficient of filters increases. This will cause the shortage of Field Programmable Gate Array(FPGA) MACs, increase the system delay and device cost. According to group delay of pulse shaping FIR filter and base band modulated symbol character, a new implementation method for Pulse Shaping FIR filters based on Look-Up-Table(LUT) of FPGA is proposed. The results of software and hardware simulation demonstrate the method is area-efficient without any accuracy loss.

Abstract:Most of blind channel identification algorithms cannot estimate the channel with common zeros and are sensitive to the channel order error. A Semi-Blind(SB) channel identification method is proposed in this paper. Through this algorithm, the channel matrix is decomposed into a same dimensional matrix and a unitary matrix in the form of their product based on Singular Value Decomposition(SVD). By using the received data and some known symbols to solve same dimensional matrix and the unitary matrix respectively, the closed form solution of channel response is obtained. The proposed algorithm effectively overcomes many limitations of blind channel identification algorithms. It avoids the selection of optimal weighted parameter of the traditional semi-blind methods. It is stable and robust to channel noise and channel order. Simulation results verify the effectiveness and superiority of the proposed algorithm.

Abstract:The corresponding solutions are proposed to tackle with the disadvantages of conventional oilfield Geographic Information System(GIS), including inconvenience of Client/Server(C/S) mode operation and maintenance, being unable to perform real-time online Point of Interest(POI) rendering, being incapable of segmentation and location according to regions, etc. An oilfield information query system of Browser/Serve(B/S) framework based on AJAX+JSON+HTML5 is designed and implemented. Experimental results show that the POI real-time rendering and regional segmentation improve on their interactivities, and the experiences of users are enriched, which meets the actual requirements of oilfield development. This work has paved the way for the development of diversified network services.

Abstract:Linear Frequency Modulation(LFM)-M code hybrid modulation pulse compression signal is designed in order to further improve the detection performance of radar. Classified comparison is used to research the application of such three classic neural networks as Back Propagation(BP) network, Elman network, and Radial-Based Function(RBF) network to pulse compression. Three network structures are designed, and their corresponding network algorithms are analyzed. Through the research on simulation and pulse compression output performance, it is indicated that a faster convergence rate and better numerical stability can be obtained in the pulse compression of LFM-M code signal by adopting RBF neural network, with the output main-to-side lobe of about 60 dB.

Abstract:An algorithm for rapidly estimating the frequency hopping transition time based on compressive samplings is proposed, in order to estimate the frequency hopping transition time of the Frequency-Hopping signal accurately and rapidly under the condition of non-cooperation. Firstly, the frequency hopping signal is acquired by slide sampling, at a sampling rate far slow than that of the Nyquist sampling. Then the first two sparse coefficients with the maximum weight of Frequency-Hopping signal are reconstructed. Based on the relationship between the different slide time and the time of the hops before and after, the frequency hopping transition time is estimated. Simulation results show that this algorithm can estimate the hopping transition time of Frequency-Hopping signal effectively, and its speed is superior to traditional algorithm based on time-frequency analysis.

Abstract:Conventional Capon beamforming algorithm has relatively high sidelobe gain. The array output performance will degrade or even become invalid when there is a mismatch in the desired signal steering vector. To solve this problem, a sparse constraint Capon beamforming algorithm is proposed. The algorithm can reduce the sidelobe, and bears robustness of the desired signal uncertainty; whereas its performance will degrade when dealing with the complicated situations in which the array amplitude errors, phase errors, and desired-orientation errors exist simultaneously. A novel sparse robust Capon beamforming algorithm is put forward in this paper. It adds a deviation steering vector to the sparse Capon under worst-case performance optimization. Simulation results demonstrate the validity and superiority of this proposed algorithm.

Abstract:A simplified model algorithm based on vertex normal vector is presented aiming for real-time rendering of large-scale three-dimensional terrain problem. In the rendering process，blocks are cut quickly by the projection of body views; the data blocks which are apart from body views are discarded; and the partially visible or fully visible blocks are loaded into the memory. This algorithm constructs node resolution evaluation function according to the distance(between the viewpoint and the node) and the roughness of the terrain as well. It eliminates cracks by adding points. Simulation results show that the proposed algorithm can reduce the number of triangles and the time required to render the terrain effectively.

Abstract:The single-channel blind separation of GMSK(Gaussian Minimum Shift Keying) mixing signals is researched. The GMSK mixing signals can not be separated by the Per-Survivor Processing (PSP) algorithm directly, therefore, linear approximation processing of the GMSK signal is considered, which enables GMSK signal to be separated by the PSP algorithm. This algorithm separates the GMSK mixing signals by maximum likelihood estimation in the joint space of the symbol sequential and the channel parameters, reserves the best path and outputs the symbol pairs to get the separated signals. Simulation results show that the bit error rate performance produced by the PSP algorithm on separating the GMSK mixing signals is slightly better than that produced by the particle filtering algorithm; and the complexity of the proposed PSP algorithm is much smaller.

Abstract:A modified algorithm for parameter identification of moving blur images is proposed based on the spectrum analysis in order to improve detecting quality of the direction and pixel for moving objects in blurred image. The relationships among dark fringe width, image size, inclination angle and kinematic scale, kinematic pixel are derived. The twice Fourier transform is applied to meet refinement of bright fringe. And then the relationship between inclination angle of fringe and moving angle is analyzed. A new algorithm for eliminating the cross bright line is proposed by analyzing its generation reasons and position. Radon transform is applied to the processed image, and the moving direction and the moving pixel are obtained according to the transform results. Simulation results show that the proposed algorithm can detect the moving direction and pixel of different sizes of blur images with a detection error under 0.5° and two pixels.

Abstract:Bag of Visual Words(BoVW) is the main solution in the current image classification field, whereas the synonymity and ambiguity of the visual words restrict the semantic expression ability of the model and reduce the accuracy of image classification. Aiming to the problem, an adaptive soft assignment method is proposed. Firstly, it analyzes the distance of the Scale Invariant Feature Transform(SIFT) features mapping to visual words, classifies these SIFT features according to certain rules, and applies adaptive allocation strategies to SIFT features with different fuzziness. Then, this paper analyzes the correlations between visual words and image categories via Chi-square model, and then removes the Visual Stop Words(VSW) and reconstructs the histograms. Finally, the images are classified by Support Vector Machine(SVM). The experimental results show that, the method can effectively reduce the impact of the visual words synonymity and ambiguity, and enhance the distinction of visual words, so as to improve the image classification accuracy.

Abstract:According to the requirements of safe, simple and nondestructive radiation effect investigation of semiconductor devices, the method of laser simulation was proposed and greatly promoted. Compared with large-scale facilities, laser simulation has various unique advantages. It helps understand the ionization radiation effect in depth and is an effective low-cost, table-top supplement for the hardness assurance. Its research shows great significance for radiation effect study in both theory and practice. In this paper, the basic principles of the interactions of γ and laser with semiconductor devices are firstly presented. Then the physical basics and characteristics of laser simulation are given, with the research progress review followed. The existing problems of current research are deeply discussed providing with feasible research approaches. In the end, necessary research contents in the future are proposed.

Abstract:The relationship between temperature drift and adhesive is investigated, based on the finite element approach and principle of servo feedback sandwich accelerometer, to cope with the temperature drift of sandwich type accelerometer. It is found that the temperature drift is changed with the changes of thickness, Young’s modulus of adhesive and the thickness of glass. When the thickness of adhesive increases from 15 μm to 35 μm, the temperature drift decreases by about 25%. When the modulus of adhesive varies from 4 GPa to 0.25 GPa, the temperature drift decreases by about 25%. When the thickness of glass adjacent to adhesive increases from 400 μm to 1 000 μm, the temperature drift decreases by about 37%. Meanwhile, it is indicated, by the comparison between the experiment data and the drift brought by the adhesive, that the temperature drift induced by the adhesive is about 1/4 to 1/3 of the experiment data. The exploration might be helpful for the understanding of relationship between temperature drift and adhesive of sandwich type micro-accelerometers.

Abstract:The Spatial Light Modulation(SLM) technology has been widely applied to the fields of threshold switch, high speed optical interconnection and optical logic operations, which demands good performance on the real-time and fast optical signal addressing. Compared with Electro-Addressing SLM(EA-SLM), Optically-Addressing SLM(OA-SLM) shows great advantages of fast speed and high resolution by parallel addressing. Nevertheless, how to achieve fast and stable optically addressing is the key point in practice. Based on ZnO thin film as a photoconductive layer, Liquid Crystal OASLM(LC-OASLM) is designed and fabricated; the modulation of the readout light intensity and phase distribution in the two-dimensional space is achieved effectively.