Vojnotehnicki glasnik / Military Technical Courier

27-39

Authors: Đorđević Miroslav Lj.

For telecommunication purposes, a monopole antenna is usually positioned on the tank turret. At low frequencies the whole tank has to be treated as a part of the antenna system. In this paper a method for electromagnetic modeling of metallic structures is presented and applied to the analysis of radiation of a tank monopole antenna. Radiation simulations are performed at the frequency range from 1MHz to 30MHz. A special attention is given to the analysis of the effects of increased elevation of the tank main gun to the radiation pattern of the antenna. The analysis of the radiation of the tank monopole is performed with and without the presence of conducting ground. It is shown that the increase in the main gun elevation at certain frequencies can lead to degradation of uniformity of radiation in the horizontal plane. Introduction Informational technologies and reliable and secure communications are an important part of a modern military doctrine. Regarding telecommunications, armored vehicles and tanks in particular present a specific problem. In this paper, a theoretical basis of the electromagnetic analysis of metallic structures and a modeling technique will be presented. The effect of the tank on the radiation pattern will be investigated both for a tank in free space and above the conducting ground. Method of moments The method of moments (MoM) is a method for an approximate solution of integral equations. This section presents the fundamentals of the MoM and the higher-order quadrilaterals as the basic elements used for geometry modeling. The currents in our method are approximated using high-order two-dimensional polynomials. Modeling of the tank geometry The tank is modeled using only 28 elements, out of which 10 bilinear quadrilaterals and 18 second-order surfaces. The monopole antenna is modeled using one straight wire segment. Results The use of the polynomial current approximation yields a reduction in the number of unknowns required for the analysis, compared to classical methods that use linear current distribution defined on small triangles. The analysis of the tank from 1MHz to 30MHz, with a 1MHz step, requires from 130 to 337 unknowns and about one minute of the CPU time on a Dell Vostro 1015 laptop computer. Tank in free space At low frequencies, the monopole-tank system acts as a dipole antenna and the computed directivity is 1.76dBi, almost equal to that of a short dipole. The elevation of the tank main gun does not influence the radiation pattern much at low frequencies. In the resonant range, the effect of the main gun elevation is much more pronounced. At 17MHz, the difference between the minimum and the maximum of radiation in the horizontal plane is 1.22dB, 1.90dB, and 2.33dB for the main gun elevation of 0°, 13°, and 20°, respectively. The effect of conducting ground The effect of the conducting ground (in this paper we assume the ground is perfectly conducting) is taken into account using the image theory. Since the original currents and their images are electrically close at low frequencies (their distance is small compared to the wavelength), their mutual coupling cannot be neglected. Once again, at low frequencies the whole structure acts as a short dipole antenna and the computed directivity is 4.76dBi; at the same time, the radiation pattern in the horizontal plane is almost uniform. At the frequency of 13MHz, however, the difference between the minimum and the maximum of the radiation in the horizontal plane is almost 8dB for the main gun elevation of 20°. Conclusion This paper presented an electromagnetic modeling and an analysis of the monopole antenna positioned on the tank turret. The antenna was analyzed at frequencies from 1MHz to 30MHz, and the effect of the main gun elevation on the antenna radiation pattern was studied. It was determined that at low frequencies the elevation of the gun does not influence the radiation pattern much, but at higher frequencies, where the tank can be considered as a resonant structure, the detrimental effect on the radiation pattern can be quite substantial. At the frequency of 13MHz, the range of communication in the horizontal plane can be almost cut in half for certain directions if the elevation of the main gun is 20°.

62-80

Authors: Borisov Mirko A., Banković Radoje D., Drobnjak Siniša M.

Geomorphometric exploration applied in the military terrain analysis is based on the GIS methodology of spatial analyses and is related primarily to military terrain analyses. It includes relief assessment aiming at producing ground clearance charts for the analysis of terrain maneuverability and its deployment, cover and concealment possibilities. An evaluation analysis of geomorphological parameters was performed for the Avala test area using a few terrain parameters (visibility, terrain aspect and slope) as well as some terrain qualitative categories (e.g. vegetation density). Terrain slope Slope and aspect are morphometric terrain parameters that can be derived directly from the DTM using some GIS operations. Slope is the first derivative of a surface and has both magnitude and direction. Slope is perhaps the most important aspect of the surface form, since surfaces are formed completely of slopes, and slope angles control the gravitational force available for geomorphic work. Mathematically, the tangent of the slope angle is the first derivative of altitude, and it is a tangent or percent slope as this surface parameter is generally referred to. Slope is defined at each point as the slope of a plane tangent to the surface at that point. In practice, however, slope is generally measured over a finite distance, especially when data are obtained from a contour map. Terrain aspect Aspect is also the first derivative of a surface and has both magnitude and direction. The term aspect is defined as the direction of the biggest slope vector on the tangent plane projected onto the horizontal plane. Aspect is the bearing (or azimuth) of the slope direction, and its angle ranges from 0 to 360°. Analyses of terrain slope and ground clearance for military forces The analysis of land assessment of the Avala test area included the definition of relief categories in relation to cover and concealment purposes with the aim to include the geomorphological basis into the standard military procedure OCOKA (Observation and fields of fires; Cover and concealment; Obstacles and movement; Key terrain; Avenues of approach). A few parameters of relief significantly influencing the possibilities for cover and concealment (visibility, slope and aspect) were included into the definition of the model of terrain spatial analysis The morphometric data included in partial assessment categories were determined on the basis of the digital model relief analysis and by using GIS tools and given morphometric relief exploration methods. Analysis of vegetation effects on ground clearance for military forces Vegetation, in addition to terrain slope, presents one of the main factors in cross-country analyses and ground clearance assessments. In classification and extraction of vegetation from satellite images, numerous algorithms of two basic classification types, supervised and unsupervised classification, are applied. Supervised classification requires the identification of cover types of interest by user. Samples of pixels are then selected, based on available ground real information to represent each cover type. These samples are called training areas. The selection of appropriate training areas is based on the analyst's familiarity with the geographical area and his knowledge of the actual surface cover types presented in the image. Thus, the analyst 'supervises' the categorization of a set of specific classes. Unsupervised classification basically reverses the supervised classification process. Spectral classes are grouped first, based solely on the numerical information in the data, and then they are matched by the analyst to information classes (if possible). Programs, called clustering algorithms, are used to determine the natural (statistical) groupings or structures in the data. The analyst usually specifies how many groups or clusters are to be looked for in the data. In addition to specifying the desired number of classes, the analyst may also specify parameters related to the separation distance among the clusters and the variation within each cluster. The result of this iterative clustering process may result in some clusters that the analyst will want to combine subsequently, or clusters that should be broken down further on - each of these requiring a further application of the clustering algorithm. Thus, unsupervised classification is not completely without human intervention. Study area and THE used data The Avala hill test area, located in the central part of the Republic of Serbia, has been mapped extensively over the years and several GIS layers are available at various scales. The study area corresponds with one sheet topographic map at a scale of 1:25 000 (TM25 430-3-1) produced in the Military Geographical Institute (MGI). The main geomorphometric features of the test area include hill summits and shoulders, eroded slopes of small valleys, valley bottoms, a large abandoned river channel, and the river terrace. The elevation of the area ranges from 70 m to 500 m with an average of 195.05 m and a standard deviation of 56.7 m. The basic sources of information were the SPOT 5 image and the digital elevation model generated from the contour lines.

96-110

Authors: Jevtović Milojko V., Pavlović Boban Z.

A topological analysis of the structure of telecommunications networks is a very interesting topic in the network research, but also a key issue in their design and planning. Satisfying multiple criteria in terms of locations of switching nodes as well as their connectivity with respect to the requests for capacity, transmission speed, reliability, availability and cost are the main research objectives. There are three ways of presenting the topology of telecommunications networks: table, matrix or graph method. The table method is suitable for a network of a relatively small number of nodes in relation to the number of links. The matrix method involves the formation of a connection matrix in which its columns present source traffic nodes and its rows are the switching systems that belong to the destination. The method of the topology graph means that the network nodes are connected via directional or unidirectional links. We can thus easily analyze the structural parameters of telecommunications networks. This paper presents the mathematical analysis of the star-, ring-, fully connected loop- and grid (matrix)-shaped topology as well as the topology based on the shortest path tree. For each of these topologies, the expressions for determining the number of branches, the middle level of reliability, the medium length and the average length of the link are given in tables. For the fully connected loop network with five nodes the values of all topological parameters are calculated. Based on the topological parameters, the relationships that represent integral and distributed indicators of reliability are given in this work as well as the values of the particular network. The main objectives of the topology optimization of telecommunications networks are: achieving the minimum complexity, maximum capacity, the shortest path message transfer, the maximum speed of communication and maximum economy. The performance of telecommunications networks is analyzed in particular. Efficiency as an integral feature of reliability represents a measure of satisfying specific requirements of the mission (adequacy) over time (reliability) in a certain moment of time (availability). Today, modern telecommunications networks face another condition: the operation in extreme conditions (major floods, catastrophic earthquakes, forest fires, electromagnetic jamming and bombing from aircraft or remote control posts). In order to realize communication in such circumstances, it is necessary to introduce a new parameter - network survivability. The network survivability is defined as the ability of a network to maintain communication features while establishing, maintaining and terminating connections in extremely difficult conditions. This paper proposes a comprehensive definition of telecommunications networks including the network survivability as a very important factor. The best results in terms of network survivability are obtained by the network with full connection, but the drawback is its high implementation cost. The grid network is more favorable since it results in reducing the number of links between network nodes. With the number of branches increasing, the delay in the network also increases. The previous analysis shows that the average path length and the average length of links are critical values when selecting a configuration of functionally resistant telecommunications networks.

121-148

Authors: Pejanović Miloš J.

The development of personal computers and Internet technology causes continuous changes in methodological approaches and concepts of development of information systems. Most existing information systems, due to their heterogeneity, have a problem of integration of subsystems. In order to overcome this problem, software vendors offer different solutions. In this work we explore different approaches and propose an optimal way, with a special emphasis on its application in the military organization. By applying modern approaches in the development of information systems on the concept of distributed component systems, we come to the set of proposed solutions from different manufacturers. The solutions are related to the mechanisms which should ensure that components written in different languages cooperate with each other in heterogeneous systems that are in different nodes in the computer network. This work describes the concept of component distributed information systems of Internet technology and their capabilities and offers a solution specifying the implementation environment in the military organization. Access to the development of information systems In the development of information systems, an important role is given to the choice of appropriate methods and tools. For large systems such as military organizations, standardized procedures and methodologies for the development of information systems are recommended. There are different methodological approaches in the development of information systems: a systematic integrated approach to development (from design, implementation to implementation and maintenance) and development of information systems as technical - technological structures (standard computer and network service). The combination of these two approaches leads to the concept of 'open systems' that allow different standards and IT services to operate on these systems. The UML system description of the process of software development has many different but interconnected models: use case model, analysis model, design model and implementation model. The previously mentioned methods of development of information systems can be systematized and described in a unique way called the Larmanova method, usually through several stages: 1.Specification request 2.Analysis, 3. Design, 4.Implementation and 5. Testing. Development of information systems in a military organization The problem of development of information systems in the Internet environment by using software components is reduced to finding ways of determining a set of methodological procedures, concepts and approaches from the repositories of methods that support distributed information systems in Internet technology. Therefore, it is necessary to design a methodological approach that will be adaptive in accordance with the specific characteristics of military organizations. While developing their information systems, most foreign armed forces use standardized procedures and methodologies applied in their environment. In cases where it is not specifically defined, there is a tendency to use modern methodological procedures in accordance with technical and technological development. Component distributed information systems with an object-oriented approach in the Internet environment The usage of distributed objects can create client/server applications with a three-layer or multi-layer architecture which enables the implementation of synchronous or asynchronous solutions for the Internet and intranet. An example of a direct execution of transactions is an approach that relies on the CORBA model (Common Object Request Broker Architecture) and the Object Request Broker (ORB). However, the applications that use them are difficult and expensive to maintain. It is one of the reasons why the development of component models has become popular and experienced great development in recent years. Components with the implemented mechanism for performing transactions can be thus used in developing new applications. The component model allows easier changes and maintenance, and also shortens the time required for implementation, because there are various ready-made components that can be used. This approach to the implementation of transactions is called the declarative approach. Developers are free of care for the realization of mechanisms for controlling the execution of transactions. Important component models are implemented in COM + technologies (Component Object Model), EJB (Enterprise Java Beans), CORBA (Common Object Request Broker Architecture) and SOA (Service Oriented Architecture). Technologies for the implementation of component distributed information systems with an object-oriented approach in the Internet environment The results of testing with different communication models for remote component calls resulted in the following technologies: COM + / DCOML, CORBA / IIOP, EJB / RMI / IIOP and SOAP. Web Services represent the basic building blocks of future information systems, and in fact are applications available on the network and suitable for executing what is necessary at that moment. The main communication protocol is SOAP, ie. XML over HTTP. They can be created from the already made applications or from the start, while programming languages, finished components and platforms can be used by the user's choice. SOAP represents the environment for message exchange based on XML in the network and it uses the HTTP protocol application used by Web servers. Implementation of component distributed information systems with an object-oriented approach in the Internet environment From the aspect of this study, it can be concluded that there are two approaches through the J2EE (Java 2 Platform Enterprise Edition) environment and the Microsoft. NET set of technologies. SOAP is a new approach to professional development of distributed applications. It solves major problems with the platform and language dependences. It is able to work over the Internet and represents an open standard maintained by the W3C (the World Wide Web Consortium). The drawback of SOAP is interoperability which is not always 100% practicable with CORBA, ie. the existing implementation does not always meet the required reliability. This may be one of the causes of an insufficient number of available Web services on the Internet. The implementation of SOAP is possible in almost any programming language, on all popular platforms, so it has the potential to create a transparent web of services and applications that can be accessed on demand by everyone from every point, which will lead to the explosive growth of new services and therefore profits. SOAP does not try to replace CORBA or any other distributed system. Compared to CORBA, SOAP is less powerful, but it is impressive in its simplicity and scalability, which is very useful from the aspect of need for a wider acceptance by companies and by developers. SOAP is still developing, and a number of new protocols will appear, simplifying and facilitating the implementation of Web services in all business areas, including military information systems. Conclusion The possibility to connect the existing solutions is of great importance in determining the development strategy of information systems in the Army as well as in other complex organizational systems that contain heterogeneous hardware and software platforms. The research and analysis of the application of these standardized concepts, technologies and development platforms, including the experience of foreign armed forces lead to the conclusion that the concept of development of information systems in the Internet environment by using software components is a recommendation for strategic determination to overcome incompatible and unrelated existing partial software solutions. The basic idea is based on Web services which can be created from finished applications or from the start, while programming languages, finished components and platforms can be used by the user's choice. The applications for mutual remote communication used to use Remote Procedure Calls - RPC such as DCOM and CORBA, or they used to be completely unrelated. The SOAP protocol allows communication between applications on different operating systems, on different platforms, written in different programming languages. The world organization W3C12 has already published the SOAP version 1.1 as re commendation. and it continues with the development of the recommendation of the SOAP version 1.2. The applications exchange messages of the agreed format. Since the messages are formatted as XML documents, their processing and testing is simple and can be realized by any program designed to work with XML documents. The SOAP client creates an XML document that contains the corresponding request. This document is formatted in accordance with the SOAP specification. The document comes to the SOAP protocol which processes incoming requests and based on the received requests launches the appropriate application. Upon completion of processing, the SOAP protocol returns a response message to the SOAP client. It is, therefore, concluded that the data transformation relates to the use of the XML format. Web Services represent the basic building blocks of future information systems, ie. in fact they may be available applications on the military network. When the decision on a type of service is concerned, it is not decisive whether the standard Web service will be implemented or a specific, particularly developed one, for example for military use. In other words, these are resources which are addressable using a URL and which return the information to the user. Analyses determine the SOAP communication protocol ie. XML over HTTP. It also concluded that the main initiator of these changes is XML which through its simplicity allows the practical independence of applications and systems because it is understandable both for a man and a machine.