Search

The detection performance of radar is significantly impaired by active jamming and mutual interference from other radars. This paper proposes a radio signal modulation recognition method to accurately recognize these signals, which helps in the jamming cancellation decisions. Based on the ensemble learning stacking algorithm improved by meta-feature enhancement, the proposed method adopts random forests, K-nearest neighbors, and Gaussian naive Bayes as the base-learners, with logistic regression serving as the meta-learner. It takes the multi-domain features of signals as input, which include time-domain features including fuzzy entropy, slope entropy, and Hjorth parameters; frequency-domain features, including spectral entropy; and fractal-domain features, including fractal dimension. The simulation experiment, including seven common signal types of radar and active jamming, was performed for the effectiveness validation and performance evaluation. Results proved the proposed method's performance superiority to other classification methods, as well as its ability to meet the requirements of low signal-to-noise ratio and few-shot learning. [ABSTRACT FROM AUTHOR]

Currently, the bore shape in an electromagnetic launcher is usually a rectangle, round, or an inverted arc. A comparison of the current density distribution, induction gradient, moment of inertia, contact pressure, contact state, structure manufacture, and launching precision between the rectangle and inverted arc bore shapes was carried out. We got some results about the effect of bore shape on the electromagnetic launcher. The results show that the inverted arc shape performed better than the rectangle in these areas: current density distribution, induction gradient, moment of inertia, contact state, and the accuracy of armature running. [ABSTRACT FROM PUBLISHER]

To make launch weapons with further range, higher energy density, better target accuracy, and better control ability are the aims pursued by people for many years. This paper divides the history of launch technology into four stages, which are the biologic, mechanical, chemical, and electromagnetic launch stages. The development trend of the launch technology is discussed, particularly the advantages of the electromagnetic launch (EML) technology. Recently, China has paid great attention to many new technical fields, such as the EML technology. China's programs are mainly confined to fields of basic research, which are collected together in this paper. However, the numbers of papers published from the 12th symposium to the 16th symposium suggest that there are more and more programs in the EML field. [ABSTRACT FROM PUBLISHER]

To analyze the variation of magnetic field waveforms above rails of the railgun during the launching period, the magnetic fields are measured by loop probes. According to the armature's different moving statements and measurement positions, magnetic waveforms are distinguished with each other. The experiment results show that magnetic field waveforms above the rails change at different positions, and the output voltages of probes become larger with the higher velocities. The truncated waveforms expand the spectrum of signals around the rails. The waveforms at different positions are compared with each other, which can inflect the magnetic field distribution along the rails during the launching period. The results are useful in analyzing the interference of the transient environment for the rail launcher and the electromagnetic interference design of railgun systems. [ABSTRACT FROM PUBLISHER]

Several loops are placed at one side of the rails along a straight line, and the transient current is calculated with the measured magnetic field waveforms and distances between probes and currents for the long-line current models. According to the skin effect and the deformation of rails, distances between currents and probes are hard to get for each shot. If two probes are used together, it is easier to measure the single line current waveform, without measuring the distance between probes and currents beforehand. The current waveforms can be calculated only with the calibrated distance between two probes and field waveforms. For the railgun's rail currents, we can use three loop probes. The current waveforms can be easily obtained from the three magnetic field waveforms without knowing the shift positions of the rail currents. The commercial Pearson current monitor model 1423 is used to calibrate and verify the results. The results are compared with each other for the single loop, two loops, and three loops. The results show that, while it is good to measure the transient currents with one or two loops, it is better when three loops are used. The method is especially useful for situations in which the huge Rogowski current probes are hard to use because of limited space. [ABSTRACT FROM PUBLISHER]

An elastic simulation model in launching is established when the insulation material is not neglected. According to the model, muzzle velocity and launching efficiency are simulated under different contact pressures. The relationships of muzzle velocity with different initial contact pressures are studied. Based on the simulation, the experiment of initial contact pressure between the armature tail and rail is developed and the launching test is studied under different contact pressures. On account of the result of simulation and test, the contact performances are optimized. When the insulation material is not neglected, the muzzle velocity will not reduce continuously. When the initial contact pressure increases, it has the best value. Based on the test result and rail surface condition after disassembling, the best contact pressure is obtained. [ABSTRACT FROM PUBLISHER]

In this paper, using the B-dot probe at the end of the gun, the B-dot's voltage waveform is measured when the armature is being launched. During the launch process, the magnetic field around the probe changes. According to the change of the magnetic field, the probe generates an induced voltage. The Hilbert spectrum of voltage signal is obtained by the Hilbert-Huang transform (HHT). Based on the Hilbert spectrum, the rail states of the launch system are compared. The results show that the waveforms obtained from the B-dot probes at the rail-gun breech can be used to analyze the whole process of the launch based on HHT. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]