Abstract:A low RCS (radar cross section) 2×2 OAM (orbital angular momentum) array antenna is designed based on the phase controlling metasurface.The array antenna is composed of four aperture coupled micro\|strip antennas, and a feeding network with same amplitude and the phase values of 0°, 90°, 180°, and 270° for different ports, realizing the OAM radiation effect of mode 1. According to the principle of phase cancellation to reduce RCS, a meta\|surface is constructed based on two units of artificial magnetic conductor with around the array antenna being loaded in the form of a checkerboard array, realizing effective reduction of antenna RCS. The simulated results show that the operating bandwidth of the array antenna is from 4.22 GHz to 5.16 GHz, and the gain is 8.91 dBi. The array antenna achieves the reduction of 8 dB RCS from 5.3 GHz to 7.0 GHz, and the reduction of 10 dB RCS from 5.35 GHz to 6.05 GHz.

Abstract:Being simple in preparation, low at the costs, and flexible in beam control, multi-beam reflected array is very popular. In this paper, a design method of dual-channel independent multi-beam reflected array is proposed based on the polarization multiplexing meta-surface, and radiation pattern fast prediction is utilized together in combination with the algorithm to calculate optimal phase configuration. Specifically, the independent dual-and the multi-beam manipulations in dual-polarization are analyzed theoretically, and simulated by the electromagnetic software. The reflected array presents good radiation performance, consisting with the simulations especially in main lobe. As an experimental verification, a prototype is fabricated and tested in a standard microwave anechoic chamber, and the measured results are in accord with the simulations. The proposed reflected array has promising ability to generate the arbitrary and independent multi-beams, largely enhancing the information capacity of the meta surfaces, offering untapped potentials in wireless communication systems and multi-target radar systems. Being simple in preparation, low at the costs, and flexible in beam control.

Abstract:A novel method for efficient anomalous reflection and refraction based on Surface-Circuit-Surface Metasurface (SCSMS) is proposed in this paper. Being different from traditional Phase Gradient Meta-surface (PGM), first, the proposed SCSMS is to convert incident spatial waves to guided waves by surface antennas, and then gradient phase distribution is to realize by adjusting the length of the back-loaded circuit. Finally, the wave is to be transmitted to the free space by the surface antenna, achieving the desired wave front control. By this way, unwanted coupling effects between units can be eliminated. To illustrate the principle of the proposed wave front regulation method, two SCSMS are designed for anomalous reflection (20°-50°) and refraction (0°-50°) respectively. The simulation results show that high efficient anomalous reflection and refraction can be achieved with efficiency of 68% and 79% respectively. And this program provides an effective case for efficient anomalous reflection and refraction with large rotation angles or other types of wave front operations using SCSMS.

Abstract:Studying to the needs of electronic attack and defense in reality of weaponry, this paper focuses attention on the application of meta-materials for the field of electromagnetism, reviews briefly the evolution and practical application of electromagnetic meta-materials, and introduces the fields which have been most potentially disruptive technologies in recent years, i.e. intelligent cloaking technology and smart cloaking weapon systems. Basing a long-term research on electromagnetic cloaking & novel electromagnetic devices in combination with workings in industry, the paper analyzes the difficulties faced with a current meta-material cloaking technology to be further improved, and makes suggestions and outlooks for future development.

Abstract:Most of modern aircraft control surface employ redundant actuation system in active mode. Due to the inherent force-fighting in this system , the traditional aircraft structural load measurement method based on on-station load calibration test is no longer suitable for the flight measurement of hinge moment of modern aircraft control surface. In this paper, a method of measurement for hinge moment of aircraft control surface based on off-station load calibration test and on-station load verification test is presented, the corresponding load measurement model is established, the factors affecting the precision of hinge moment measurement are analyzed and determined, the verification and correction methods of possible systematic errors are given, the procedure for flight measurement of hinge moment of aircraft control surface is developed. The feasibility and effectiveness of this method are verified by flight test of hinge moment measurement of multi-type aircraft control surface, the precision of hinge moment of aircraft control surface is improved, and the reliable measured load is provided for the design load verification and optimization of aircraft control surface. The load distribution of each actuator of aircraft control surface is obtained, and flight monitoring of the force-fighting of the actuation system of aircraft control surface is realized, which ensures the flight safety.

Abstract:The structural integrity of landing gear doors affects the safety of aircraft during takeoff and landing. In this paper, a method of indirectly monitoring the structural health of the landing gear door by using the strain of the door link is proposed. Firstly, a strain gauge is pasted on the landing gear outer door link of a certain type of transport aircraft to qualitatively analyze the aerodynamic force of the landing gear door during retraction and retraction; Then, the time-frequency analysis and frequency spectrum analysis of the connecting rod strain data are carried out by using the wavelet change and Fourier change to obtain the vibration response frequency of the outer door of the landing gear. The vibration response frequency is taken as the vulnerable detection value, and the evolution of the structural damage of the door is judged according to its change trend, and compared with the natural frequency of the door to analyze the cause of the structural damage; Finally, the airborne test system and monitoring system are used to realize the health monitoring of landing gear door structure during flight. The results show that this method is reliable and effective, which can detect the structural damage of landing gear door in advance, and has the value of popularization and application.

Abstract:In response to the problem of slow computation speed of the existing airspace characterization model based on the grid profile of latitude and longitude, which has large grid deformation at high latitudes, and the conflict detection algorithm that determines whether the airspaces overlap with each other by the airspace boundary coordinates, we propose to characterize the airspaces with the full equal rhombic discrete grid based on the large circular arc profile of the spherical rhombic discrete grid of positive icosahedron, and use the multi-level Hilbert space filling curve to encode the airspaces uniformly by combining the airspace priority. A matrix-based digital airspace representation method is designed, and the Hadamard product operation is used to quickly determine whether there is a conflict between the space-use attributes of multiple airspaces. The simulation results show that the method has high grid accuracy, achieves second-level conflict detection, and can achieve the purpose of reducing the algorithm operation and improving the operation speed compared with the traditional conflict detection algorithm.

Abstract:Aiming at the uncertainties of various conditions and tasks in the reentry gliding vehicle, an local model based on-line trajectory adjustment algorithm is proposed by the combining of off-line trajectory optimization and on-line trajectory adjustment. Off-line Radau-pseudospectral solution is used for trajectory characterize and local trajectory model construct, with the local model set constructed by the trajectory constraint space discretization. A method of local model subset construct and updating based on fuzzy membership degree is proposed by introducing the idea of fuzzy clustering, with the on-line generation of trajectory realized by the means of trajectory weighted fusion. Finally, the trajectory generation and on-line adjustment performance of the algorithm are verified by simulation analysis.

Abstract:Aimed at the problems that in the air combat, the traditional CRITIC (Criteria Importance Though Intercriteria Correlation) method is hard put to assess situation to achieve variable weights, assigning weights are only begging from the attributes of the data itself, expert opinions are neglected, and the CRITIC method itself makes image jitter, a sliding window CRITIC-G1 based close air combat situational assessment method is proposed. The method is to pre-processes the air combat data to obtain a dominance function matrix with change according to time, decompose the dominance function matrix by adopting the sliding window method, and assign CRITIC-G1 weights to the dominance function matrix in the sliding window, achieving both variable weights and the importance ranking-based weighting optimization. Simultaneously, the coefficient of variation is introduced to reduce the combined dominance function image jitter. The final output is the combined dominance function values of the aircraft, and the results of the situational assessment are obtained by analyzing the combined dominance function values of the two aircraft. The experimental results show that the sliding-window CRITIC-G1 method is an accuracy increase of 22.75%.

Abstract:This paper studies the back-propagation neural network (BPNN), the particle swarm optimization back-propagation neural network (PSO-BPNN), the firefly-optimized back-propagation neural network (FA-BPNN), and the Fibonacci-optimized back-propagation neural network (IM-FSM-BPNN) for the tracking of the maximum power point of photovoltaic modules under local shadows, and the above-mentioned algorithms fly photovoltaic power generation tracking in solar drones. The results show that: First of all, under partial shading, the power prediction accuracy of IM-FSM-BPNN is the lowest, the tracking time is the longest, and the robustness is poor, the reason is the large number of control parameters and the dependence on the initial values of the parameters. The power pre-diction accuracy of FA-BPNN is the highest and the robustness is better, because it can effectively avoid the problem of gradient disappearance during the training process. Secondly, In the increase of sample data and the application of solar drones, it is found that the prediction effect of the FA-BPNN is good and the limitations of the IM-FSM-BPNN . Finally, the influence of parameter changes on the prediction results is discussed. IM-FSM-BPNN, PSO-BPNN and FA-BPNN are more suitable for multi-sample data prediction than BPNN, and IM-FSM-BPNN is more suitable for smaller learning rates than the other three algorithms. The average tracking time and power average prediction accuracy of the four algorithms fluctuate with the number of hidden layer nodes.

Abstract:Phase shifter is a key component in wireless communication system and phased array radar receiver, which is used to regulate and equalize signal phase. In this paper, a numerical control phase shifting element based on differential circuit structure and RC element is proposed. The phase shifting element can gain the phase difference of output signal through a scanning pulse control of the differential tube in turn. The phase shifting value can be adjusted by changing the parameters of RC element. An eight-stage cascade model is constructed by using the proposed Numerical Control(NC) phase shifter element, and a 360° tandem NC phase shifter is realized. Simulation results obtained by Multisim software verify the effectiveness of the design of NC phase shifter, and the test results of hardware implementation show that the design of multistage tandem NC phase shifter works well with high precision of 1.4°, and realizes the phase shift control in the full cycle range. The realization of the NC phase shifter provides an important technical support for the timely and flexible calibration of the phase error of the receiving system.

Abstract:Both the advantages of phased array radar imaging and the multiple input multiple output (MIMO) radar imaging being taken into consideration, a multi-target high-resolution imaging method based on hybrid MIMO phased array technology is proposed. In the method, the transmit array (TA) is used to replace the transmit antenna in the traditional MIMO radar, and the TA works in the hybrid MIMO phased array mode. Each TA is divided into multiple sub-arrays (SA) according to the number andthe direction of targets. The internal element in each SA works in the phased array mode to form a transmission beam into pointing to a target in a certain direction, while each SA transmits mutually orthogonal waveforms, workingafter MIMO mode. Beam-forming of the echo signal of each SA can obtain higher signal-to-noise ratio (SNR) and signal-to-interference ratio (SIR). On this basis, a single shot high-resolution imaging method and a multiple shot high-resolution imaging method are proposed respectively in combination with the dictionary optimization, the orthogonal matching pursuit and the parametric sparse representation. The simulation results show that the proposed method can achieve better imaging performance and real-time imaging.

Abstract:Micro-Doppler feature is an important reference for target recognition of ballistic missile. In high frequency radar system, the position relationship between warhead and radar directly affects the generation of radar echoes and micro-Doppler feature extraction subsequently, so the influence of occlusion effect must be considered. Firstly, the 3D Max software is used to model the geometry of cone warhead, and the 3D mesh model of the warhead target is obtained. Secondly, for the warhead vertex and empennage scatterers, the average normal vector method is used for occlusion judgment on the basis of plane hidden and elimination algorithm from the Computer Graphics, then the more real simulated echoes of target is obtained, which makes a preliminary exploration on echoes modeling and micro-motion characteristics analysis of ballistic targets under the occlusion condition. 