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Estimation and Management of Performance Limiting Factors in the Development of 1 kW Peak Power Pulsed Fiber MOPA at 1550 nm
Get PDFAn all-fiber three-stage master oscillator power amplifier (MOPA), based on Erbium and Erbium-Ytterbium co-doped fibers, has been designed and developed. The performance of such a laser is primarily limited by amplified spontaneous emission (ASE), Yb bottlenecking, and non-linear effects. Other important factors, that need to be considered towards performance improvement, are fiber bend diameter and heat generated in the fiber. This paper describes the methodology for the estimation and management of these limiting factors for each amplifier stage. The work presented here is limited to the fibers which are commercially easily available, unlike customised Yb- free large mode area (LMA) Erbium-doped fibers, where very high peak and average powers are being reported due to the absence of Yb ASE. Presented experimental results and discussion shall be beneficial for the fiber laser amplifier designers. With suitable management, 1 kW peak power pulses of 30 ns duration at 200 kHz repetition rate have been achieved with 30 % optical efficiency. The collimated output of 6 W average power (limited by Yb ASE) with high beam quality (M2 ≈ 1.6) at 1550 nm can be employed for a variety of applications. By adding additional amplifier stages, power can be scaled further
Design of Magnetic Focusing system for a Compact Ka band Helix TWT
Get PDF In this paper we discuss the design of Magnetic focusing system (MFS) for a compact helix travelling wave tube (TWT) operating in Ka-band. Issues related to the design of the magnetic focusing system have been discussed in detail along with practical measurement results. The key design parameters considered for this TWT are: the cathode voltage is around 9.3kV, beam current is 200mA and total length of the tube not more than 6 inch with minimal weight
Design and Development of High Power Broad Band Dry RF Load
Get PDFHigh power S-Band ferrite based RF load is designed and developed which is capable of handling 3 kW average power at operating frequency 2998±20 MHz . Electrical and thermal design is carried out using CST Studio Suite. Mechanical parts are fabricated according to the design. Water cooling is provided to the absorbing ferrites to support high power operation. Various RF load parts are fabricated, chemically cleaned and brazed. The experimental return loss better than 30 dB for a bandwidth of 250 MHz is achieved. The numerical and experimental results are discussed and presented in this paper
Deep Learning based Cryptanalysis of Stream Ciphers
Get PDFConventional cryptanalysis techniques necessitate an extensive analysis of non-linear functions defining the relationship of plain data, key, and corresponding cipher data. These functions have very high degree terms and make cryptanalysis work extremely difficult. The advent of deep learning algorithms along with the better and efficient computing resources has brought new opportunities to analyze cipher data in its raw form. The basic principle of designing a cipher is to introduce randomness into it, which means the absence of any patterns in cipher data. Due to this fact, the analysis of cipher data in its raw form becomes essential. Deep learning algorithms are different from conventional machine learning algorithms as the former directly work on raw data without any formal requirement of feature selection or feature extraction steps. With these facts and the assumption of the suitability of employing deep learning algorithms for cipher data, authors introduced a deep learning based method for finding biases in stream ciphers in the black-box analysis model. The proposed method has the objective to predict the occurrence of an output bit/byte at a specific location in the stream cipher generated keystream. The authors validate their method on stream cipher RC4 and its improved variant RC4A and discuss the results in detail. Further, the authors apply the method on two more stream ciphers namely Trivium and TRIAD. The proposed method can find bias in RC4 and shows the absence of this bias in its improved variant and other two ciphers. Focusing on RC4, the authors present a comparative analysis with some existing methods in terms of approach and observations and showed that their process is more straightforward and less complicated than the existing ones
Aerodynamic and Structural Optimisation of Maritime Patrol Radar System Radome using Evolutionary Algorithms
Get PDFAirborne early warning systems are deployed for collecting surveillance information on airborne enemy targets in real-time. The Maritime Patrol Radar system is used for surveillance of sea surface for various types of ships and low flying aircraft. Radio Detection And Ranging system, or RADAR, in short, is an Electromagnetic sensor integrated on such airborne platforms. An antenna of this radar system is generally mounted under the belly of the aircraft and protected by a cover called a radome. This radome is installed to protect the radar antenna from environmental disturbances. Due to the installation of the radome, increased drag is experienced by aircraft during its flight due to resistance to the flow of the oncoming air. Radome design is a multidisciplinary effort involving structural, aerodynamics, and electromagnetic disciplines. In this study, the multi-disciplinary design of the maritime patrol aircraft radome for optimality in terms of structural strength and aerodynamic performance is carried out by integrating both disciplinary analyses on an optimisation software platform. The utopia point in terms of these two disciplines is found
A New Multi Echelon Repair Network Model with Multiple Upstream Locations for Level of Repair Analysis Problem
Get PDFLevel of repair analysis (LORA) determines (1) the best decision during a malfunction of each product component; (2) the location in the repair network to perform the decision and (3) the quantity of required resources in each facility. Capital goods have long life cycles and their total life cycle costs are extremely high. LORA, which can be done repeatedly during the life cycle of the product, both at design and product support phase, plays an important role in minimising the total life cycle costs of capital goods. It is mostly applied to systems that operate in different geographical areas and deployed in different regions, which include different subsystems with special technology and expertise, and have a complex product structure. In this study, we propose a new mathematical model to the LORA problem, which is more comprehensive and flexible than the other pure LORA models in the literature. The proposed model uses the multiple upstream approach that allows the transfer of the components from a location in the lower echelon to the predefined locations in the upper echelon and determines the material movement paths between each facility, defining the facilities’ locations in the repair network. The performance of the proposed model is tested on benchmark instances and the results are compared with the single upstream model. Computational experiments show that the proposed model is more effective than the single upstream model and reduces the total life cycle costs by 4.85% on average, which is an enormous cost saving when total life cycle costs of capital goods are considered
Context aware Routing to Assist Routing Decisions for Quality Improvement in Multi Hop Ad hoc Networks
Get PDFThe context information is an intriguing aspect of decision making. The context-awareness can be useful in the ad hoc networks in which nodes are mobile, and the conditions are dynamic. In ad hoc networks, routing protocols are intended to discover the route over multi-hop wireless links under varying conditions. The context-awareness can assist the routing protocols in determining the appropriate path. This paper investigates into choosing the appropriate route by applying the context information and presents the approach to improve the decision making and the quality of the route. We consider nodes, connecting links, and different layers as the context. The paper introduces the scalability and flexibility in the set of parameters that govern the eminence of the node inter-connection that, in turn, influences the overall quality of the route. We propose the context-aware dynamic routing protocol (CADR) and present the approach, algorithm, and analysis. We simulate the protocol by taking the flexible combination of the context attributes and the values, also compares the performance with AODV. The simulation results show that the protocol chooses the appropriate route as per the considered attributes and weight, and provide the enhanced performanc
A Wide Beam Printed Quadrifilar Helix based Circularly Polarised Radiating Element for Electronically Steered Antenna
Get PDFWide beam and low axial ratio performance of printed quadrifilar antennas result in very attractive circularly polarised radiating element for wide scanned Electronically Steered Antenna. A compact printed quadrifilar Helix antenna (PQHA) has been designed and realised at S-Band frequency. Simulation and optimisation of designed antenna has been performed using ANSYS’s high frequency structure simulation (HFSS) software for its impedance, axial ratio (AR) performance and radiation characteristics. The developed circularly polarised antenna has 3-dB beam width of 130° and peak gain of 3.4dBic at 2.6 GHz. The developed antenna shows excellent AR performance over the frequency band as well as over the radiated beam. Half power axial ratio bandwidth of developed antenna is 27.4% (2.2 GHz - 2.9 GHz) while the impedance bandwidth is 32% (2.1 GHz - 2.9 GHz). Design has been validated through measured results. Designed wide band PQHA can be used as radiating element for electronically steered antenna for large beam steering application
Asymmetrical Vortex over Slender Body A Computational Approach
Get PDFComputational investigations were carried out on an ogive-cylinder configuration having a slenderness ratio of 7.5. The geometry of the nose tip was generated based on the physical geometry of the nose tip observed under a scanning electron microscope. Time-dependent simulations were performed on the slender body at a diameter Reynolds number of 3.0×104. Results indicated that the onset of vortex asymmetry was mainly due to the micro-tip imperfection existing at the tip. It was also observed that the variation in the roll angle of the model affected the flow physics largely which has been experimentally observed by several researchers in the past. The computed results were in better agreement with the referenced experimental data
Experimental Studies of Resin Systems for Ablative Thermal Protection System
Get PDFThe present work was initiated to finalise resin for the development of thermal protection system (TPS) for the external surface of a polymeric composite rocket motor case made up of Carbon roving and Epoxy resin. The temperature on the outer surface of the composite case increases due to kinetic heating caused by aerodynamic drag and vehicle velocity. These rocket motor casings are functionally required only in the ascent phase of missile trajectory till motor action time and stage separation. Due to which the experienced heat flux is relatively less, and the temperature on the external composite case is in order of 250 °C - 300 °C depending on missile configuration and trajectory, unlike extreme thermal conditions on ablative nozzle liners exposed to rocket motor exhaust. The maximum allowable temperature in the present study for the Carbon-Epoxy case is 100 °C due to degradation in mechanical properties. The thermal protection system on the external surface will function as a heat-insulating layer based on the working mechanism of ablation. The resin of the thermal protection layer has a substantial impact on the manufacturing process and curing aspects, especially compatibility with the pre-cured carbon epoxy case layer. The generation of test results for thermal stability, cure characteristics and Tg for Epoxy resin has also been included in present studies as an additional objective that provides significant inputs for process development. The test results for Epoxy resin is also used as a basis for the finalisation of resin for the thermal protection layer for processing aspects apart from its basic thermal stability characteristics. The ablative thermal protection working mechanism is based on the ablation phenomenon. In the case of ablation, resin plays a vital role due to pyrolysis and other thermal characteristics. In the present experimental studies, the Phenolic resin and Silicone resin are considered as candidate resin materials for ablative thermal protection system based on available literature and in house experience. The main objective of the present studies is to evaluate thermal stability, char yield after final decomposition through DSC and TGA techniques for both resins as these are fundamental characteristics needed for the present specific application. The test results for specific grades (formulation) of phenolic and Silicone resins are generated and compared. In the present work, the experimental studies to evaluate glass transition temperature (Tg), thermal stability, and cure characteristics for Epoxy resin is also carried through DSC. The test results of specific grade Epoxy resin provides a basis to assess thermal margins for resins selected for ablative thermal protection system and inputs for process development and design requirements. The scope of the present studies is aimed to finalise the resin system for external thermal protection of composite rocket motor case based on thermal characteristics test results and other compatibility aspects with the structural layer