This paper analyzes the basic theory of rapid rotating scanning scheme for the off-axis 45° parallel two-mirror system, and constructs the transformation action matrix of optical vector in the rotating scanning process. Based on simulation with MATLAB, the relationship between the four control parameters of rotating scanning scheme for the off-axis 45° parallel two-mirror system and the scanning trajectories is analyzed in-depth, and the basic conditions of the control parameters are determined to achieve various scanning strategies. The performances of two scanning strategies (Linear scanning in any direction and Elliptical scanning in different ranges) are analyzed in detail. The scanning scheme discussed in this paper has the advantages of simple control, high scanning efficiency (100%), and flexible scanning strategy and so on by scanning with mirror rotating. It can realize the functions of rapid scanning for imaging with high linearity, region ergodic searching, random or complex path for searching and so on.
In order to realize multi-function, the radar has wide instantaneous bandwidth and working bandwidth. Unfortunately, the traditional phased array radar antenna by microwave phase shifter in the way of phasing. This paper presents a kind of optical beamforming network based on cascaded micro-ring resonator. The simulation results show that the proposed antenna system can be more effectively satisfied with requirement of wideband and wide-angle scanning of phased array radar.
In order to realize multi-function, the radar has wide instantaneous bandwidth and working bandwidth. Unfortunately, the traditional phased array radar antenna by microwave phase shifter in the way of phasing. This paper presents a kind of wideband phased array antenna based on array element micro-ring resonator delay and subarray optical switch, and performance simulation to the proposed antenna system. The simulation results shows that the proposed antenna system can be more effectively satisfied with requirement of wideband and wide-angle scanning of phased array radar.
In order to realize multi-function, the radar has wide instantaneous bandwidth and working bandwidth. Unfortunately, the traditional phased array radar antenna by microwave phase shifter in the way of phasing. With the increasing demands of radar network performance in terms of bandwidth, distance and synchronization accuracy of information transmission links, microwave photonic radar network is gaining great attention from researchers. This paper analyzes key technologies in microwave photonic optical beamforming networks, reviews the recent advancement and discusses its possible research directions in the future.
The aperture diaphragm of the Cook-TMA optical system is set on the secondary mirror, which improves the symmetry of the system. It has features of large field of view and small f-number, and suitable for infrared optical system. However, the system has no Lyot stop and low efficiency of cold diaphragm. A new method is proposed in this paper. First, Cook-TMA off-axis three-mirror reflection system is designed according to the requirements of field of view and f-number. Second, the aperture diaphragm is moved to a place behind the tertiary mirror and before the image surface, which becomes Lyot stop in fact. At this time, the beam obstruction problem arises. Starting with large f-number, we adjust and optimize gradually to solve the obstruction problem until the f-number meets the requirements. According to this method, three-mirror reflection optical system with off-axis field of view and off-axis aperture is designed with the f-number 1.6 , the field of view 11° by 1°, grid distortion less than 2%, imaging quality closed to the diffraction limit, which is suitable for imaging in infrared wavelength band.
When the off-axis two reflection optical system is applied to the infrared system, it faces the contradiction between Wide FOV and small F#. The off-axis three reflection system can increase field of view in the symmetrical direction but difficult in the asymmetric direction. This paper explores a method to solve this problem. First, a three-mirror reflection system is designed with off-axis field of view and aperture according to requirements of field of view and F# in the symmetrical direction. The field of view in the asymmetric direction is set at about 1°, and the aperture diaphragm is placed in front of the image plane to form Lyot Stop. Then the main mirror is planarized and removed that the secondary mirror and the tertiary mirror can form an Anti-telephoto structure, the field of view is increased in the asymmetric direction. Finally, the dimensional constraints are established to avoid occlusion and adjust and optimize this system. According to this method, a double off-axis two reflection optical system suitable for infrared imaging is designed with the f-number 1.6, the field of view 7°×7°, the distortion less than 3% and the imaging quality close to the diffraction limit.
Optical beamforming network is the core part of microwave photonic phased array radar. In this paper, the principles and features of different optical beamforming network technologies are proposed and analyzed, which provide certain theoretical support for applications in engineering practice. The future development of research work in this field is finally given and prospected.
In order to realize multi-function, the radar has wide instantaneous bandwidth and working bandwidth. Unfortunately, the traditional phased array radar antenna by microwave phase shifter or direct digital synthesis in the way of phasing. There are two limitations after increasing the instantaneous bandwidth: "beam squinting" and "aperture traverse delay", which cause the beam divergence and the beam broadening. In this paper, the integrated optical beamforming network technologies are discussed analyzed, which provide certain theoretical support for the research of the future multi-band broadband reconfigurable radar and even the engineering of microwave photonic radar.
An improved Blackman Harris apodization function is studied for rectify the shortcomings of large main lobe width of Blackman Harris apodization function in apodization processing of Fourier transform spectrometer. The basic principle of apodized interferogram is analyzed. The Chebyshev function with tunable parameters is introduced to improve Blackman Harris function. Compared with the original function through Matlab simulation, the improved apodization function shows not only the characteristics of main lobe width is enhanced, but also the side lobe attenuation can be adjusted, so the function is more flexible in engineering application.
Endmember extraction technology of ballistic missile is an important research content in spectral remote sensing, which can effectively solve the mix pixel problem. This paper starts with the background requirement of near space and research content of mixed spectral endmember extraction. The algorithm of spectral endmember extraction based on non-negative matrix factorization for ballistic missile in near space background is proposed and analyzed. The simulation results show that the proposed algorithm demonstrates the good performance in the condition of random mixing mode and correlation mixing mode.
The infrared detection technology of ballistic missile based on near space platform can effectively make up the shortcomings of high-cost of traditional early warning satellites and the limited earth curvature of ground-based early warning radar. The operating range of the infrared system based on the near space platform is the key index for detecting ballistic missile. In order to analyze the operating range of infrared detection system based on near space platform, an improved range equation from investigating the characteristics of point source target is discussed and deduced. The simulation results show this method has scientific guiding significance for system overall scheme demonstration and design technically.
The infrared detection technology of ballistic missile based on near space platform can effectively make up the shortcomings of high-cost of traditional early warning satellites and the limited earth curvature of ground-based early warning radar. To estimate the detection range of near space-based infrared system for boost-phase ballistic missile, the background infrared radiation as well as ballistic missiles is analyzed in detail. As for the lack of applicability and accuracy of the role distance algorithm which based on the performance contrast, the wave number to the radiation flux formula is introduced. The detection ranges of skin, plume and tail nozzle for boost-phase ballistic missile at 4.25 to 4.55μm are simulated under various conditions. The results show that the improved algorithm can provide the certain engineering application value for the design of near space-based infrared system.
The infrared detection technology of ballistic missile based on near space platform can effectively make up the shortcomings of high-cost of traditional early warning satellites and the limited earth curvature of ground-based early warning radar. In terms of target detection capability, aiming at the problem that the formula of the action distance based on contrast performance ignores the background emissivity in the calculation process and the formula is only valid for the monochromatic light, an improved formula of the detecting range based on contrast performance is proposed. The near space infrared imaging system parameters are introduced, the expression of the contrastive action distance formula based on the target detection of the near space platform is deduced. The detection range of the near space infrared system for the booster stage ballistic missile skin, the tail nozzle and the tail flame is calculated. The simulation results show that the near-space infrared system has the best effect on the detection of tail-flame radiation.
The propagation characteristics of the orbital angular momentum in vortex waves have been studied. The representation of electric multipole radiation filed is derived from the Laugerre-Gaussian beams to electromagnetic vortex. Simulation results show the capability of using the orbital angular momentum for remote imaging.
The ballistic missile hyperspectral data of imaging spectrometer from the near-space platform are generated by
numerical method. The characteristic of the ballistic missile hyperspectral data is extracted and matched based on two
different kinds of algorithms, which called transverse counting and quantization coding, respectively. The simulation
results show that two algorithms extract the characteristic of ballistic missile adequately and accurately. The algorithm
based on the transverse counting has the low complexity and can be implemented easily compared to the algorithm based
on the quantization coding does. The transverse counting algorithm also shows the good immunity to the disturbance
signals and speed up the matching and recognition of subsequent targets.
An improved anomaly detection and classification algorithm based on high-order statistics is presented. In order to solve some challenging problems, such as initializing projection, quantifying of anomaly classes and evaluating the performances. Firstly, initialize the projection vectors used by the idea of global RX algorithm. It gives priority to the detection of the anomalies with powerful energy. Secondly, analyze the current data whether have anomaly information or not so that it determines the terminal conditions and the quantities of anomaly classes. Thirdly, use two methods to evaluate the classification performance quantitatively. One is to match the results in the condition of reference images to evaluate the effects of anomaly detection and background suppression, the other is to segment the resultant images to calculate some features such as the classification rate, the number of detected anomalies and the number of false alarms. Simulated and Experimental results show that the improved algorithm has the capability of robustness and better anomaly detection performances under complex unknown background than traditional algorithm does.
KEYWORDS: Signal processing, Receivers, Single mode fibers, Optical communications, Photodiodes, Telecommunications, Systems modeling, Dispersion, Channel projecting optics, Linear filtering
In this paper, we propose an effective possibility density functions method of channel estimation with Viterbi algorithm
based on transitions. We also investigate the performance of the electronic dispersion compensation schemes via this
new channel estimation method. The schemes Simulation results show that it exhibits the similar performance with the
sophisticated MLSE scheme.
The applications of Electronic Dispersion Compensation (EDC) have recently attracted attention for high speed long
haul transmission. Moreover, recent progress in signal formats has gained interest in recent years such as Differential
Quadrature Phase Modulation (DQPSK). This format has higher spectral efficiency and reduced symbol rate compared
to binary modulation compared to binary modulation formats. In this paper, we investigate the application of different
EDC schemes with DQPSK format against chromatic dispersion (CD). The schemes are nonlinear feed-forward
equalizer (FFE) and Decision-Feedback equalizer (DFE) and butterfly FFE-DFE. We demonstrate that butterfly structure
can mitigates nonlinearity of cross-coupling because of processing two DPQSK tributaries independently. A 40 Gb/s
simulated transmission system over 160km length is established. Simulation results show that butterfly FFE-DFE has
better performance than separate FFE-DFE.
KEYWORDS: Optical communications, Receivers, Telecommunications, Eye, Distortion, Transmitters, Computer simulations, Signal processing, Linear filtering, Digital signal processing
This paper discusses electronics dispersion compensation (EDC) by decision feedback equalizer (DFE) in high speed
optical communication system using the LMS and the RLS algorithms, respectively. The theory of the decomposed DFE
derived from basic concept of DFE in EDC is studied. Compared with the traditional DFE, the system complexity of new
one has been reduced while it still keeps the high performance of DFE. Simulation results prove the validity of
practicability and indicate that the decomposed DFE using RLS algorithm can more effectively eliminate intersymbol
interference (ISI) after being transmitted long distance.
Walsh-Haar function system that was first intruoduced by us is a new kind of function systems, and has a good global/local property. This function system is called Walsh ordering function system since its generation kernel functions belong to Walsh ordering Walsh function system. We worked out a recursive property of the matrix corresponding to the first Walsh-Haar functions in Walsh-Haar function system, and we also proved that Walsh-Haar function system is perfect and orthogonal similar to Walsh function system and Haar function system. Thus, discrete Walsh-Haar transformation (DW-HT) is an orthogonal transformation that can be widely used in signal processing. In this paper, using the recursive property of the matrix and the fast algorithm of discrete Walsh transformation (DWT) in Walsh ordering, we have designed a fast algorithm of Walsh ordering DW-HT based on the bisection technique. The idea and method used in this paper can be used for designing fast algorithms of other ordering DW-HTs and other discrete orthogonal transformations.
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