Abstract:The experiment of damage effect on Si bipolar transistor-low noise amplifier injected the microwave pulse in experimental platform. In the failure analysis of Si bipolar transistor-low noise amplifier with microwave pulse, the transistor was permanently damaged when the gain of lownoise amplifier decreased more than 10 dB. The electrical characteristic of the Si bipolar transistor was measured before and after its damage and the micro-characteristic of the damaged transistor was observed by scanning electron microscope. Results show that when the Si bipolar transistor is damaged with microwave pulse, the ablative Si material in the base region causes short circuit of emitter junction and collector junction, which have the consequences of losing the PN junction characteristics and leading to failure devices.

Abstract:As one of the energy storing elements of explosively-driven flux compression generators, the pulsed capacitor was required to discharge only once, such as explosively-driven flux compression generators. Therefore, it provided a possibility to make the pulsed capacitor working in overstress. Compared with the overstressing capacitor, the pulsed capacitor has several advantages, such as small volume and light weight. So it could be used as a current driver to miniaturize explosively-driven flux compression generators. The overstress characteristics of metalized polypropylene pulse capacitor (MPP capacitor) were investigated at different temperatures. Experimental results show that the energy storage density is 1.8 times of the rated energy storage density at the temperature of-45~60℃, and in this condition, the oneside lower confidence limit of reliability is 0.9 if the confidence level is 0.95.

Abstract:P-Spice was used to analyze the influence of stray parameters, including self-inductance of the pulse capacitor and the inter-turn capacitance and the impedance of the winding in magnetic switch, on output characteristics of the series magnetic pulse compressor. Results show that inter-turn capacitance and the impedance in unsaturated state of the winding make minor influence on the output waveform. However, the impedance in saturated state of the winding reduces the voltage efficiency of the system, conspicuously. Moreover, the self-inductance of the pulse capacitor not only reduces the voltage efficiency but also influences the rise-time of the output voltage waveform. Based on former results, the single stage magnetic pulse compressor system was optimized and a series magnetic pulse compressor, with peak voltage of 26kV, whose pulse rise-time is compressed from 4.1s to 1.2s and whose voltage efficiency is over 92.5% was developed. 

Abstract:Electrons traversing a transparent medium emit Cerenkov light when the electron velocity exceeds the velocity of light in the medium. A time-and-space resolved optical diagnosis system based on Cerenkov radiation for the uniformity of intense electron beam diode has been founded. Before the operation of a series experiments, Particle-in-cell and Monte Carlo simulation codes were utilized to design the experiment structure. The emission uniformity of two kinds of velvet sample was studied. It was found that the carbon velvet cathode has much bigger central enhancement zone and the Cerenkov radiation light of the area near the edge is also brighter. The operating state of diode can be obtained by analyzing the time evolutions of Cerenkov radiation light which achieves 10ns~100ns temporal resolution.

Abstract:A high impedance relativistic klystron amplifier with a cold solid cathode is designed and investigated by 2.5-D particle-in-cell simulations. The model is composed of a diode with a shielding ring, five pill-box cavities and a cone collector. In order to simplify and minimize the cathode structure, a cold cathode is designed and adopted in a high-impedance relativistic klystron amplifier with rather high conversion efficiency. A shielding ring is introduced to achieve the desired high impedance and reduces the surface electric field to avoid unexpected explosive emissions and ensures the emission uniformity. In the beam-wave interaction region, with optimization of the position of the last two cavities and the magnetic field, the performance of the klystron is validated. It reveals that microwaves with a power of 81 MW are generated at a frequency of 11.424GHz when the beam voltage and current are 525kV and 328 A respectively, under a guiding magnetic field of 0.35 T. The corresponding power conversion efficiency is as high as 47%, and the gain reaches 49 dB when the net injection power is 1 kW.

Abstract:To solve the problems of impure output modes and inefficient TEM transmission in the Ku-band MILO with the conventional uniform coaxial extractor, a gradual transitional coaxial extractor was proposed. The simulation results show that: the gradual transitional coaxial extractor achieves efficient microwave extraction and a single output TEM; the transitional coaxial structure is conductive to the design of supports and meets TEM transmission requirements. Compared with the traditional extractor, the gradual transitional coaxial extractor can strengthen the beam-wave interaction and accelerate the microwave start-up through enhancing the quality factor of the Ku-band MILO in right amount.

Abstract:Backward wave oscillator with over-mode Ka-band high power microwave (HPM) generally outputs mixed TM0n modes, it has high energy conversion efficiency, but it can′t ensure the purity of output modes. However, it is necessary for high radiation efficiency that the microwave input to the radiation terminal is certain single and pure. So it is hard to put these HPM sources into application. In order to solve this problem, a design method for compact hybrid modes converter of purifying TM0n mixed modes was proposed. With this method, the TM01, TM02 and TM03 mixed modes can be converted into pure circular waveguide TM01 mode efficiently on the condition of high power capacity and wide wave band. This method also reduces the modes purification difficulty in the design of the HPM sources.

Abstract:A compact relativistic magnetron with axial output for TE₁₀ mode was investigated. This magnetron with 6 resonant cavities operates at πmode and can well transit between resonant cavities and rectangular output waveguide through the structure design of 4 cavities axial output, which realizes the microwave output of rectangular TE₁₀ mode. Compared with the magnetron with diffraction output (MDO), this design not only makes both the diameter and the axial length of the magnetron minimized so that the whole system can be more compact, but also provides a much purer output mode of a low order in the output waveguide. The operating performance of the magnetron has been analyzed and optimized by using particle-in-cell simulation software. Simulation results show that the power conversion efficiency can reach to 25.0%, corresponding to the output power of 10GW and the working frequency of 2.58GHz, under the condition of the applied voltage of 500kV and the applied magnetic field of 0.5T.

Abstract:Backward wave oscillator with over-mode Ku-band high power microwave (HPM) generally outputs mixed TM_0n modes, it has high energy conversion efficiency, but it can′t ensure the purity of output modes. However, it is necessary for high radiation efficiency that the microwave input to the radiation terminal is certain single and pure. So it is hard to put these HPM sources into application. In order to solve this problem, a design method for compact hybrid modes converter of purifying TM_0n mixed modes was proposed. With this method, the TM₀₁,TM₀₂ and TM₀₃ mixed modes can be converted into pure circular waveguide TM₀₁ mode efficiently on the condition of high power capacity and wide wave band. This method also reduces the modes purification difficulty in the design of the HPM sources.

Abstract:A novel TM₀₁ mode high power microwave phase shifter is proposed which is composed of two crossed circularly polarized TE₁₁ mode converter. The phase of the output microwave can be adjustable in a range of 0°~360°. The electromagnetic behaviors of the circularly polarized TE₁₁ mode converter and the phase shifter are simulated by the software CST. The results show that the output microwave can be adjustable in a range of 0°~360°at the frequency of 1.75GHz with the error is not more than 1 °, the transmission efficiency in this range is larger than 97%, and the power capacity is larger than 4.3GW.

Abstract:The single channel method of anti-navigation frequency interference mainly utilizes the prior knowledge of the interference in observed data received by the large antenna for interference mitigation, the performance of the interference mitigation is weakened in the case of the relatively lower interference-to-noise ratio in the observed data. A channel-assisted interference mitigation method for radio astronomy by parametric estimation and subtraction is proposed. To achieve the purpose of eliminating the interference signal, the proposed method utilizes the observational data received by auxiliary antenna having a higher interference-to-noise ratio to establish the estimation model of interference parameters, at the same time by constructing the difference parameters estimation model of the main and auxiliary channel to correct the estimation model. Simulation results indicate that, compared with the single channel method, the proposed method is more broadly applicable to eliminate the interference in the lower interference-to-noise ratio conditions for radio astronomy.

Abstract:To improve the frequency efficiency and the transmission performance of differential chaos shift keying under wireless fading channel, a multi-carrier chaotic shift keying communication scheme is proposed. In each block size of M OFDM symbols, one pilot OFDM symbol inserted time-spaced in all-frequency is used to transmit the reference chaotic signal and the other M-1 OFDM symbols is used to transmit the informationbearing signals, which spread by the reference chaotic signal. At the receiver, a differential detector is constructed and the information bits from the correlations between the pilot OFDM symbol and the other M-1 OFDM symbols in each block size of M are recovered. A multi-carrier chaotic shift keying transceiver under MIMO multipath fading channels with no channel state information is presented, in which a distinct chaotic sequence at each transmit antenna is used to spread the same data symbol and the detection statistics at each receive antenna are combined with equal gain for symbol detection. Both performance analysis and computer simulations show that multi-carrier chaotic shift keying outperforms differential chaos shift keying in additive white Gaussian noise channels with high bandwidth efficiency for the block size of M>2 and that multicarrier chaotic shift keying achieves both spatial diversity gain and frequent diversity gain under MIMO multipath fading channels.

Abstract:It is unclear that what color descriptors best fits feature matching of aerial remote sensing Bayer real-color image. To analyze variation of imaging of the aerial image and algorithm characteristics of color descriptors, a theoretical analysis of invariant properties of color descriptors was presented. The effect and applicability of descriptors were verified and analyzed by three experimental methods which are evaluations of simulation data, different categories images and general applicability of task. The theoretical and experimental results show that RGBSIFT has best applicability for the feature matching of aerial Bayer real-color image. The usefulness of color descriptor is category-specific.

Abstract:In order to accurately estimate and correct the frequency nonlinearity of voltage controlled oscillator, a novel approach based on contrast optimization of range profiles is proposed, which will perform nonlinearity estimation and correction adaptively. A temperature-varying tuning model is established in the proposed method, the nonlinearity is obtained with a given temperature by using this model. The nonlinearity is removed from the beat signal, and the range profiles of targets are derived by pulse compression. According to the contrast of range profile, the real temperature is iteratively estimated. The contrast of range profile will converge toward the maximum, so an optimal estimation of temperature, which is nonlinearity, is achieved. Simulation and experimental results show that the proposed approach with consideration on environmental temperature variation can estimate and correct the nonlinearity without any additional hardware circuit. Compared with the conventional approaches, this method can not only accurately estimate and track the frequency nonlinearity of voltage controlled oscillator in realtime, but also has low hardware complexity and computing cost, which is the significant to solve the problem of voltage controlled oscillator frequency drift.

Abstract:A vectorization of accelerating fast Fourier transform computation based on fused multiply-add instruction was presented. Separate multiplication and addition operations in conventional computation were manipulated into less fused multiply-add operations by transforming process of fast Fourier transform butterfly computation, which decreased the real floating-point operations of radix-2 decimation in time fast Fourier transform butterfly computation from 10 multiplication (addition) operations to 6 multiply-add operations and decreased the real floating-point operations of radix-4 decimation in time fast Fourier transform butterfly computation from 34 multiplication (addition) operations to 24 multiply-add operations. Vector data access on twiddle factors was optimized to reduce memory cost. Experimental results show that the presented method can greatly accelerate fast Fourier transform computation and achieve efficient performance and efficiency.

Abstract:Multi-core architectures have been broadly utilized in current processors. Meanwhile, the diversity of memory access modes in applications brings challenges to the last level Cache in multi-core processors. An optimization method for the last level Cache based on the access modes is proposed. This method includes three coordinated and progressive levels:the configurable share/private Cache partition, the configurable bypass Cache policy, and the priority replace policy. Using this method, programmers can neatly alter the behavior of the last level Cache to effectively adapt the variety of memory access modes in applications. Experiment results show that the proposed method can observably decrease the miss rate of the last level Cache and increase the system performance of the processor.

Abstract:In order to study the electric field induced by magnetic hull of moving ship, a mathematical model was proposed based on Coulomb and Biot-Savart laws. The correctness of this model was verified by the experimental measurements. The model has the characteristics of wide applicability and high computational precision, on the basis of which, the induced electric field distribution of moving ship was proposed. The simulation calculation was performed using the magnetic field data of a real ship.The result indicates that the induced electric field reaches 1 mV/m around the ship, and it could be detectable.

Abstract:In order to address challenges of safety analysis of global navigation satellite systems (GNSS) brought by its system of systems (SoS) characteristics such as complex relationships between its component systems, to identify and study the SoS safety hazards across-the-board, and to improve its safety and enhance the service, a GNSS safety modeling method was proposed in the base of the functional dependency network analysis theory from the view of SoS. The effects and reasons of hazards promulgation and random failures combination caused by complex relationships between component systems in GNSS were analyzed and investigated with some emphasis. The simulation results show that the method is able to describe the influencing process of hazards promulgation and failures combination clearly and conduct both orthodromic and antidromic reasoning analysis. The results also demonstrate the great potential and applicability of the method to SoS safety analysis of GNSS.

Abstract:Carrier phase difference measurements for the same satellite navigation signal at each antenna array elements can be used to solve its direction of arrival (DOA). However, traditional tracking algorithms can only adopt separate tracking loops for each separate antenna element when moderate interference is present; these algorithms cannot obtain precise measurements and frequently become lose of lock. Aim to solve these problems, a joint carrier tracking algorithm which decomposed each element′s carrier phase to the common average part and the low dynamic residual part was proposed. For the average carrier phase, as it is commonly shared by each array element, its tracking accuracy can be improved by combining all the observation values of the whole array elements. For the residual carrier phase, its tracking accuracy can be improved by reducing the loop noise bandwidth. Theoretical analysis and numerical simulation show that the algorithm can significantly improve the measurement accuracy of carrier phase difference between elements needed by DOA estimation and tracking sensitivity. The tracking sensitivity of a 4 element antenna array with typical application conditions improves 4dB and the carrier phase difference measurement accuracy of it increases 3 times under the same carrier noise ratio.

Abstract:The algorithm of extracting quadratic expressions in the pre-processing phase of cube attack with quadratic test was enhanced to optimize the attack efficiency. The variation of secret keys was introduced into cube attack, which makes the model much more flexible. At the same time, with the help of the trade-off between time and space, the complexity of extracting quadratic terms was reduced by storing the results of the constant and linear terms. The improved method was applied to the simplified PRESENT and Trivium algorithms and it turns out that the attack efficiency is enhanced obviously.

Abstract:A posture control system based on the controlled contact force was designed to ensure there is no slipping between the foot of Acrobot(acrobatic single-leg robot) and the ground during motion. The horizontal component of the contact force was set as the control objective of the internal loop and its value was restricted by the friction cone, so that the contact consistency between foot and ground at the tracking process of the shank′s posture angle was preserved. At the upright equilibrium posture of Acrobot, the dynamic equations were linearized and the transfer function link “actuation torquehorizontal contact force-horizontal position of the center of mass-posture angle of the shank” was derived to design the multi-loop control system for the posture angle of the shank. A virtual Acrobot model was built in MATLAB by using the “SimMechanics” toolbox. Simulation results show that the designed control system can realize the tracking control without slipping between the foot and the ground.

Abstract:Comprehensive evaluation for hypersonic vehicle trajectory optimization algorithm has good reference value on selecting optimal trajectory optimization algorithm. According to the features of hypersonic vehicle, trajectory was decomposed into ascent, cruise and descent stages; the performance evaluation indices of each stage and the typical methods of weighting for performance evaluation index were given respectively. Combining with the analysis theory of grey correlation degree, a comprehensive evaluation method of trajectory optimization algorithm was proposed. The calculation results show that the method can quantitatively evaluate trajectories produced by trajectory optimization methods and sort the alternative optimization methods by merits.

Abstract:In order to improve detection ability of groundbased radar to near space hypersonic target and explore a practical and efficient deployment optimization method, the difficulties and mathematical models of the ground-based radar to detect near space hypersonic target were analyzed and the deployment principle and quantitative indicators of it were put forward. Deployment optimization model of ground-based radar was established and the ant colony algorithm controlled by introductory pheromone was designed. The simulation results show that this method can achieve a variety of programs of ground-based radar deployment optimization, improve the efficiency and operability of the ground-based radar deployment optimization, and provide a new way of thinking for ground-based radar to detect near space hypersonic target.

Abstract:Aiming at the orbital maintenance problem of super low altitude satellite for the long duration of the flight, the variation characteristics of the average eccentricity vector were analyzed and an orbital maintenance method was presented. Firstly, the change of average eccentricity vector characteristic of super low altitude satellite under the J₂,J₃ zonal terms and the atmospheric drag was analyzed. Then an orbital maintenance strategy based on energy conservation principle was proposed. Finally, the effectiveness of orbital maintenance strategy was validated by simulation examples. Simulation results show that the changes of average eccentricity is stable under the perturbation of the earth non-spherical gravity, the atmospheric drag and the impulsive maneuver, and the proposed orbital maintenance method can effectively achieve super low altitude maintenance and make the average eccentricity vector converge to equilibrium point. Besides, the fuel consumption for orbital maintenance is reasonable and the long duration flight in super low orbit can be achieved.

Abstract:In order to further improve the computation efficiency of seakeeping prediction for the ships with forward speed, the symmetry property was introduced into the calculations of velocity potentials in the 3-D translatingpulsating source Green function method. Based on the Green function′s symmetry, the specific measures were put forward to evaluate the ship hydrodynamics. By the symmetrical magnitude of source point to field point, the integral symmetry expressions of normal derivative of harmonic function at the symmetric line and surface elements were derived and obtained. The symmetrical characteristics were applied to simplify the matrix of coefficient in the boundary integral equation. A theoretical method with high efficiency was presented for the seakeeping performance of 3-D ship advancing in waves. Numerical results and example analysis show that the symmetry property of translatingpulsating source Green function is available for the minimization of computation and memory amount and is proved effective in the numerical calculations of wave exciting forces, motion responses and free-surface waveform for the advancing ship in waves. It is expected to extend the symmetrical characteristics of translating-pulsating source Green function to the hydrodynamic analyses of interacting two ships or complex ship form in frequency domain.

Abstract:For navigation using X-ray pulsars, both technique investigation and simulation were based on the X-ray pulsar signal. But practically, the observation data was unable to confirm the exact value or the analysis of validation of navigation algorithm. Therefore, it was necessary for simulation algorithms to reconstruct X-ray pulsars. Based on the fact that the arrival of photons possess non-homogeneous poisson random process, the model of the signal of X-ray pulsars was built, and the epoch folding algorithm for pulse profile construction was presented. Two existed simulation algorithms were presented. A new numerical simulation algorithm based on the reconstruction of photon TOAs (time of arrivals) was derivated from distributive function and its inverse function. To avoid approximating in the two algorithms, the derivated algorithm employed the pulse profile fitted by piecewise linear function. The signal of pulsar PSR B0531 +21 was simulated, and chi-square goodness-of-fit-test was utilized to demonstrate that the simulated TOAs complied with the poisson distribution. Comparison was implemented among the new algorithm and the existed two algorithms. Simulation result indicates that the new algorithm is superior to the existed two algorithms in photon counts and pulse profile error. Observed pulse profiles approaches to the standard template profile as observation time increases, which demonstrate that the simulation algorithm is feasible, and the X-ray pulsar signal can be reconstructed effectively. 

Abstract:A finite time convergent guidance law based on variable universe fuzzy adaptive sliding mode was proposed for intercepting high speed and maneuvering targets. Firstly, the missile-target interception model was derived and the three-dimensional sliding mode guidance law was designed. Secondly, according to the expert experience of finite time convergent guidance laws, the fuzzy adaptive control method was adopted to approximate the consecutive items of the sliding mode guidance law, and the finite time convergent control rules were designed. Finally, a new expansion factor for variable universe was proposed and the variable universe fuzzy adaptive sliding mode guidance law with finite time convergence based on new expansion factor was proposed. Simulation results show that the proposed guidance law can hit the target correctly and achieve the finite time convergence ability of the line-of-sight. Besides, compared with the proportional navigation guidance law, the proposed guidance law has better guidance precision and shorter flight time.

Abstract:A predictive model was set up to improve the prediction precision of polar motion of earth orientation parameters. The periodic characteristics of interpolated basic series was studied by Fourier analysis, the feasibility of basic series resampling was verified, then the trend terms were derived from the interpolation basic series, and the multiple input-single output BP(Back Propagation)neural network model was used to predict the residual series for different time spans. Finally the predicted polar motion was achieved by combining the trend terms with residual series. Prediction results indicate that the appropriate selection of interpolation basic series can realize high precision prediction of polar motion. Moreover, the BP neural network can be applied to the prediction of polar motion of earth orientation parameters effectively.

Abstract:As for the low centroid precision of blurry star spots acquired by the star sensor in vibration environment, the star spot centroiding model with inertial measurement information was proposed and the centroiding algorithm was formed. The weighted center of the star spot was regarded as the centroid at the initial time of the exposure by the algorithm, then the centroid track could be computed with the vibration information by the strap-down inertial sensor, and the star imaging area and its weighted center could be estimated with the star spot power distribution model. Finally, the exact centroid value at the finish time of the exposure was got by using iterative operation to make the two weighted centers coincide with each other. The centroiding precision of the algorithm and the effect of relevant factors on it are analyzed by using simulation data, and numerical results indicate that the method can reach about 0.01-pixel centroid precision even in the vibration environment with a good applicability performance.

Abstract:Considering the design of high contact ratio of double helical gears, based on the loaded tooth contact analysis technology, the bending-torsional-axial coupling dynamic model of modification double helical gears was established with the concentrated parameter method in the consideration of the special axial floating installation characteristics of pinion, the stiffness excitation, error excitation and meshing impact excitation. The dynamic equations were deduced by the newton method and the vibration acceleration of gear transmission system was obtained. A fitness approximation genetic algorithm was introduced to dispose the problem of time waste in calculating fitness. The root mean square of vibration acceleration was selected to be object function to optimize the basic design parameters and parabola modification coefficient by the fitness approximation genetic algorithm. 〖JP〗The effectiveness of the optimization method was confirmed by the given example. In the end, the noise values of original gears and optimization ones obtained by the loaded test further verify that the optimal method has certain effects on the noise reduction of gears.