Feasibility analysis of WDM links for radar applications

Active phased array antennas enhances the performance of modern radars by using multiple low power transmit/receive modules in place of a high power transmitter in conventional radars. Fully distributed phased array radars demand the distribution of various signals in radio frequency(RF) and digital domain for real time operation. This is normally achieved through complex and bulky coaxial distribution networks. In this work, we intend to tap the inherent advantages of fiber links with wavelength division multiplexed(WDM) technology and a feasibility study to adapt these links for radar applications is carried out. This is done by analysing various parameters like amplitude, delay, frequency and phase variation response of various radar waveforms over WDM links. This also includes performance evaluation of non-linear frequency modulation(NLFM) signals, known for better signal to noise ratio(SNR) to specific side lobe levels. NLFM waveforms are further analysed using pulse compression(PC) technique. Link evaluation is also carried out using a standard simulation environment and is then experimentally verified with other waveforms like RF continuous wave(CW), pulsed RF and digital signals. Synchronization signals are generated from this variable duty cycle digital signals during real time radar operation. During evaluation of digital signals, variable transient effects for different duty cycles are observed from an amplifier configuration. A suppression method is proposed to eliminate this transient effects. Further, the link delay response is investigated using different lengths of fiber spools. It can be inferred from the experimental results that WDM links are capable of handling various signals significant to radar applications.     

Research on Pulse Radiation Characteristics of Leaf-like Ultra Wide Band Antenna

A new kind of ultra wideband antenna, which consists of a leaf-like dipole and a dielectric block, is proposed and analyzed. The dielectric block is attached in parallel with the dipole near its feed point. Thus, the near field is attracted to the side where the dielectric block is located. It leads to a focusing effect of the energy in the far zone. The finitedifference time-domain （FDTD） method combined with the perfectly matched layers （PML） technique is used in the simulation of the antenna radiation characteristics. The research shows that, with proper dielectric loading and 50 Ωfeeding line, the bandwidth of the antenna can be up to 6.5 GHz, from 3.5 GHz to 10 GHz with VSWR （voltage standing wave ratio） less than 2.5.     

Deployable Antenna with Compact Ortho-mode Transducer and Feeding Systems

The compact ortho-mode transducer (OMT) and compact conical corrugated horn(CCCH) are used as feeding system of the deployable dual polarizing antenna in this paper.A new stricture of double-septum in main wave guide OMT is proposed. The finite difference method in time domain (FDTD) in combination with genetic algorithms(GAs) is used to analysis and optimize this new OMT. The experiment results show that the voltage standing wave ratio (VSWR) of this OMT and feeding system is less than 1.17 in bandwidth; the isolation between the ortho-mode ports is less than -40dB; the cross-polar level of the feed can reach -35dB and the length of the main waveguide can be reduced 50% at least.     

Application of Space-time Conservation Element and Solution Element Method in Intake and Exhaust Flows of High Power Density Diesel Engine

A one-dimensional pipe flow model of single-cylinder diesel engine is established to investigate the intake and exhaust flow characteristics of diesel engine in the condition of high power density （HPD）. A space-time conservation element and solution element （CE/SE） method is used to derive the discrete equations of the partial differential equation for the intake and exhaust systems. The performance parameters of diesel engine with speed of 2100 r/min are simulated. The simulated results are in accordance with the experimental data. The effect of increased power density on charging coefficient is analyzed using a validated model. The results show that the charging coefficient is slowly improved with the increase in intake pressure, and is obviously reduced with the increase in engine speed.     

Minimum Curvature Design of turbine Hydrodynamic Three-Element Centripetal- Torque Converters

The influence of streamline bending inertia force on power loss is investigated. In order to analyze the combined effect of the inertia force and the path on the power loss, the accumulation effect expression of the inertia force on its path is derived. The calculation result shows that the accumulation effect of the unit inertia force on its path depends merely upon the velocity magnitude and the path scroll angle. As long as they are given, the accumulation effect is a constant and independent of the intermediate path. An important conclusion drawn is that the maximum inertia force rather than its ac- cumulation effect plays a predominant role in the power loss. Thus, a new design method, minimum streamline curvature method, is proposed. Fluid particle movement inside a hydrodynamic torque converter can be regarded as curved move- ment on the circular surface and decomposed into a meridional component and a circumferential component. Each merid- ional streamline is designed to be close to a circular arc, while each torus streamline is constructed with a circular arc and a straight line segment. Based on the meridional streamline equation, the torus streamline equation and a streamlined thickness function, a blade surface equation of three-element centripetal-turbine hydrodynamic torque converter can be obtained.     

Theoretical Investigation and Experimental Verification of Passive Simulation of Metal Plate Infrared Thermal Characteristics with That of PCM

A one-dimensional thermophysical model is used to investigate the simulation of the infrared thermal signature of mental plate with phase change material（PCM） plate theoretically. The optimized parameters are obtained by the theoretical calculations. Based on the calculation results, a kind of organic PCM is selected to experir＊entally verify the model, and the good match between the theoretical and experimental results is achieved. The results of this investigation provide the design rules and key materials for the application of PCMs in false target.     

Optimal Gliding Guidance of Vertical Plane for Standoff Released Guided Bomb Unit

Optimal gliding guidance for a guided bomb unit in the vertical plane is studied based on nonlinear dynamics and kinematics.The guidance law is designed under minimum energy loss index.To avoid the complexity in solving two-point-boundary-value problems,the steady-state solutions of the adjoint states in regular equations are suggested to be used.With these considerations,a quasi-closed,optimal gliding guidance law is obtained.The guidance law is described by the angle of attack in a simple nonlinear equation.An iterative computation method can be easily used to get the optimal angle of attack.The further simplified direct computation algorithm for the optimal angle of attack is also given.The guidance properties are compared with those of maximum lift-to-drag angle of attack control.The simulation results demonstrate that the quasi-closed,optimal gliding guidance law can improve the gliding phase terminal performance with significant increase in the altitude and much little decrease in the speed.     

Experimental Study of RF-excited Diffusion Cooled Off-axis Unstable Resonator with High Frequency Modulation in a Waveguide CO2 Laser

The experimental study of the laser beam parameters of the pulse repetitive RF-excited diffusion cooled waveguide CO2 laser are presented. The measurements are carried out for the pumping pulse duration of 100 μs and pulse repetitive rates 5 - 14 kHz. The average power density delivered to the active medium is 76 W/cm^3. Three types of the pulses, namely the square, the sine and the triangular ones have been applied at the input as pumping pulses and their effects on the output power and the delay time have been studied. The output power of the radiation versus input power, pressure of the laser gas mixture and modulation frequency has been investigated. The results indicate that the output peak power for the three types of pulses increases with increase of the pressure of the laser gas mixture and with the input power where as it decreases with the repetition frequency. The delay time of the output pulse decreases with the increase of the repetition frequency and input power, where as it increases with the increase of the pressure of the laser gas mixture. The behavior of the output power and the delay time with duty cycle for square pulse has also been investigated.     

Experiments and Numerical Simulation of Small-scale Slapper Driven by Electrical Explosion

Based on the low inductance technology and parallel-plate transmission principle, an experimental apparatus of small-scale slapper initiating primary high explosives driven by electrical explosion is designed and established. The prob- lem of instantaneously and continuously measuring the velocity of the small-scale slapper is successfully solved by using the technique of laser interference. Compared with the results published on the literatures at home and abroad, data of the experimental and the numerical simulation shown in this paper are more proper to reflect the physical process of electrical explosion driving slapper. One-dimensional numerical simulation of electrical explosion driving slapper is done using the hydrodynamic code. The experimental results are consistent with the computed ones by introducing a power correction factor. In the end, the introduced power correction factor is discussed.     

Actuator characterization of a man-portable precision maneuver concept

The US Army Research Laboratory is conducting research to explore technologies that may be suitable for maneuvering man-portable munitions. Current research is focused on the use of rotary actuators with spin-stabilized munitions. A rotary actuator holds the potential of providing a low-power solution for guidance of a spinning projectile. This is in contrast to a linear （reciprocating） actuator which would need to constantly change direction, resulting in large accelerations which in turn would require large forces, thereby driving up the actuator power. A rotational actuator would be operating at a fairly constant rotation rate once it is up to speed, resulting in much lower power requirements. Actuator experiments conducted over a variety of conditions validate the dynamic models of the actuator and supply the data necessary for model parameter estimation. Actuator performance metrics of spin rate response, friction, and power requirements were derived from the data. This study indicates that this class of maneuver concepts can be driven with these actuators. These results enable actuator design and multi- disciplinary simulation of refined maneuver concepts for a specific application.     

Study on Inertial Response Performance of A Micro Electrical Switch for Fuze

The design, modeling, and simulation of a micro electlical switch for fuze are presented. It consists of spring mass system with zigzag slot in mass, latching and electlical cnnecfion mechanism and movement-lhnit mechanism. The switch keeps off-state until it is subjected to an acceleration when fuze is launched normally. The acceleration is simulated as half-shoe pulse with specific amplitude and duration. The dynamics model of the switch is studied. Based on zigzag slot in mass, the methods used for recogllizing acceleration load are estahhshed and analyzed according to the dynamics theory. Two typical half-shoe accelerations are loaded on the switch in simulation. The simulation resuhs are in accordance with those of tfieoretical analysis. The inertial response characteristics of the switch can ensure that the fuze power supply and circuit are connected safely and reliably.     

A New Filtering Algorithm Utilizing Radial Velocity Measurement

Pulse Doppler radar measurements consist of range, azimuth, elevation and radial velocity. Most of the radar tracking algorithms in engineering only utilize position measurement. The extended Kalman filter with radial velocity measureneut is presented, then a new filtering algorithm utilizing radial velocity measurement is proposed to improve tracking results and the theoretical analysis is also given. Simulation results of the new algorithm, converted measurement Kalman filter, extended Kalman filter are compared. The effectiveness of the new algorithm is verified by simulation results.     

Research on Estimation of Time Delay Difference in Passive Locating for Impulse Signal

Analyzed the relation between time delay difference and time delay estimation errors, based on the principles of three-point locating, a reformed threshold method for time delay difference estimation of impulse signals, called as amendment estimation for short, is developed by introducing channel equalization technique to its conventional version, named as direct estimation in this paper, to improve the estimation stability. After inherent relationship between time delay and phase shift of signals is analyzed, an integer period error compensation method utilized the diversities of both contribution share and contribution mode of concerned estimates is proposed under the condition of high precision phase lag estimation. Finally, a cooperative multi-threshold estimation method composed of amendment and direct estimations to process impulse signals with three thresholds is established. In sea trials data tests of passive locating, this method improves the estimation precision of time delay difference efficiently. The experiments verify the theoretical predictions.     

Topology Optimization in Damping Structure Based on ESO

The damping material optimal placement for the structure with damping layer is studied based on evolutionary structural optimization （ESO） to maximize modal loss factors. A mathematical model is constructed with the objective function defined as the maximum of modal loss factors of the structure and design constraints function defined as volume fraction of damping material. The optimal placement is found. Several examples are presented for verification. The results demonstrate that the method based on ESO is effective in solving the topology optimization of the structure with unconstrained damping layer and constrained damping layer. This optimization method suits for free and constrained damping structures.     

Waveguide Invariant and Passive Ranging Using Double Element

The sea-trial results indicate that the stable interference structure can be observed in low-frequency continuous spectra sound field.And the equation of the interference striation have been derived in light of the comcept of waveguide invariant, indicating that the striations are a family of quasi hyperbolas. The heading angle φ, waveguide invariant β and r0/v(r0 is the range of the closest point of approach and v is the navigating velocity of target) are estimated by using Hough transform for the image processing of the LOFARgram and bearing-time records. Four passive ranging algorithms based on double element or double array model are proposed. The simulation research shows that the first positioning algorithm should be adopted when the target heading angle is less than 10°; otherwise, the latter three algorithms are used to range, and the larger the heading angle is, the higher the positioning accuracy is. The relative ranging errors of the four methods are less than 10% under the simulation conditions used in this paper.     

Numerical Research on The Nozzle Damping Effect by A Wave Attenuation Method

Nozzle damping is one of the most important factors in the suppression of combustion instability in solid rocket motors. For an engineering solid rocket motor that experiences combustion instability at the end of burning, a wave attenuation method is proposed to assess the nozzle damping characteristics numerically. In this method, a periodic pressure oscillation signal which frequency equals to the first acoustic mode is superimposed on a steady flow at the head end of the chamber. When the pressure oscillation is turned off, the decay rate of the pressure can be used to determine the nozzle attenuation constant. The damping characteristics of three other nozzle geometries are numerically studied with this method under the same operating condition. The results show that the convex nozzle provides ,tre damping than the conical nozzle which in turn provides more damping than the concave nozzle. All the three nozzles have better damping effect than that of basic nozzle geometry. At last, the phase difference in the chamber is analyzed, and the numerical pressure distribution satisfies well with theoretical distribution.     

Analysis of equivalent antenna based on FDTD method

An equivalent microstrip antenna used in radio proximity fuse is presented. The design of this antenna is based on multilayer multipermittivity dielectric substrate which is analyzed by finite difference time domain （FDTD） method. Equivalent iterative formula is modified in the condition of cylindrical coordinate system. The mixed substrate which contains two kinds of media （one of them is air）takes the place of original single substrate. The results of equivalent antenna simulation show that the resonant frequency of equivalent antenna is similar to that of the original antenna. The validity of analysis can be validated by means of antenna resonant frequency formula. Two antennas have same radiation pattern and similar gain. This method can be used to reduce the weight of antenna, which is significant to the design of missile-borne antenna. Copyright . 2014, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.     

A passive method to stabilize an airborne vehicle

A method of augmenting an airborne vehicle for short-period dynamics and stability by passive means is presented in this study. A trajectory- phase disturbance rejection capability is achieved for an unguided fin-stabilized vehicle by flexible mounting of the fins to the vehicle body. The deflecting fins lag the body oscillation such that the harmonic oscillation can be quickly dampened. The amount of fin deflection may be chosen by a hinge-line location; among other things, the vehicle damping behaviour is largely determined by this choice. Linear theory is applied and 6- DOF simulations are carried out to demonstrate the approach suitability for the task.     

Single channel source separation of radar fuze mixed signal based on phasedifference analysis

A new method based on phase difference analysis is proposed for the single-channel mixed signal separation of single-channel radar fuze. This method is used to estimate the mixing coefficients of de-noised signals through the cumulants of mixed signals, solve the candidate data set by the mixing coefficients and signal analytical form, and resolve the problem of vector ambiguity by analyzing the phase differences. The signal separation is realized by exchanging data of the solutions. The waveform similarity coefficients are calculated, and the timeefrequency distributions of separated signals are analyzed. The results show that the proposed method is effective. Copyright . 2014, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.     

Experimental investigation of Tie6Ale4V titanium alloy and 304L stainless steel friction welded with copper interlayer

The basic principle of friction welding is intermetallic bonding at the stage of super plasticity attained with self-generating heat due to friction and finishing at upset pressure. Now the dissimilar metal joints are especially popular in defense, aerospace, automobile, bio-medical,refinery and nuclear engineerings. In friction welding, some special alloys with dual phase are not joined successfully due to poor bonding strength. The alloy surfaces after bonding also have metallurgical changes in the line of interfacing. The reported research work in this area is scanty. Although the sound weld zone of direct bonding between Tie6Ale4 V and SS304 L was obtained though many trials, the joint was not successful. In this paper, the friction welding characteristics between Tie6Ale4 V and SS304 L into which pure oxygen free copper(OFC) was introduced as interlayer were investigated. Boxe Behnken design was used to minimize the number of experiments to be performed. The weld joint was analyzed for its mechanical strength. The highest tensile strength between Tie6Ale4 V and SS304 L between which pure copper was used as insert metal was acquired. Micro-structural analysis and elemental analysis were carried out by EDS, and the formation of intermetallic compound at the interface was identified by XRD analysis.