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Title: USING NONUNIFORM SEGMENTS LENGTHS WITH NEC TO ANALYZE ELECTRICALLY LONG WIRE ANTENNAS
Abstract: In this paper an electrically long monopole is analyzed using the Numerical Electromagnetics Code, version two (NEC-2). Due to the electrical length of the monopole and the segment length requirement established for the NEC-2 program, the computer memory requirement and computational time become excessive. By successively increasing the segment length with distance from the source, very large structures can be analyzed accurately and efficiently. Various schemes for selecting the segment lengths are considered, and the results are compared to those obtained by using a large number of electrically short segments. This technique of grading segment lengths allows one to employ NEC-2 to analyze other electrically long wire antennas. [Vol. 5, No. 2, pp. 2-16 (l990)]
Author(s): Saad N. Tabet, J. Patrick Donohoe, Clayborne D. Taylor
File Type: Journal Paper
Issue:Volume: 5      Number: 2      Year: 1990
Download Link:Click here to download PDF     File Size: 689 KB

Title: VERIFYING WIRE-GRID MODEL INTEGRITY WITH PROGRAM 'CHECK'
Abstract: A wire-grid model of a complex surface such as an aircraft consists of hundreds of "vertex" points joined by hundreds of wires or "links". A wire antenna analysis program such as NEC is used to find the currents on the wires. The formulation within NEC imposes restrictions on the geometry of the wires, which limit the length of "segments" compared to the wavelength, the radius compared to the wavelength, the ratio of the segment length to the radius, and so forth. This paper collects these limitations together into a set of "modeling guidelines". The"integrity" of a wire-grid is its ability to represent the electrical behaviour of the continuous surface that it models. An important aspect of integrity is conformance to the "modeling guidelines". Gross errors creep into complex grids: repeated wires, omitted wires, wires of zero length. More subtle errors which violate the "modeling guidelines" can lead to incorrect current distributions and misleading radiated or scattered fields form the wire-grid when solved with the NEC code. This paper describes a program called CHECK which examines an input geometry file for the NEC program for conformance to the "modeling guidelines" by each individual wire, by wires forming junctions, and by pairs which do not join but are closely spaced. CHECK tabulates "notes", "warnings" and "errors" to aid the user in assessing the degree to which the model satisfies the guidelines. CHECK systematically finds all the guideline violations in a model. CHECK produces lists of wires for display with computer graphics to show the location of each type of problem that CHECK finds. The guideline violations found by CHECK inherently suggest improvements that can be made to the wire-grid. [Vol. 5, No. 2. pp. 17-42 (1990)]
Author(s): C. W. Trueman, S. J. Kubina
File Type: Journal Paper
Issue:Volume: 5      Number: 2      Year: 1990
Download Link:Click here to download PDF     File Size: 1753 KB

Title: SELECTING WIRE RADIUS FOR GRID/MESH MODELS
Abstract: Conducting bodies such as antennas and scatterers can be modelled by thin wire segments. However, a generally accepted and consistent criteria for selecting optimum radius for the wire segments in the model has yet to be specified. This paper presents some results rom modelling microstrip patch antennas with thin wires and the effects of wire radius on the resonance characteristics of the antenna. [Vol. 5, No. 2, pp. 43- 57 (1990)]
Author(s): L. A. Oyekanmi, J. Watkins
File Type: Journal Paper
Issue:Volume: 5      Number: 2      Year: 1990
Download Link:Click here to download PDF     File Size: 485 KB

Title: PILGRIMS PROGRESS - LEARNING TO USE THE NUMERICAL ELECTROMAGNETICS CODE (NEC) TO CALCULATE MAGNETIC FIELD STRENGTH CLOSE TO A SOMMERFELD GROUND
Abstract: This paper gives the history and a description of work performed by the authors to identify some errors and solve some problems involved in the use of the Numerical Electromagnetics Code (NEC2 and NEC3, with the companion code SOMNEC) to calculate H-fields in the vicinity of a Sommerfeld ground, and describes some of the code errors and omissions that have been identified to date. The most significant discovery has been that a section of code has been omitted from the subroutine NHFLD in NEC2, which results in incorrect calculations by NEC2 of near H-field strengths close to a real ground. It must be noted that Macfarlane, Fleming, and Iskra, have access to NEC2 only, whilst k has access to both NEC2 and NEC3. [Vol. 5, No. 2, pp. 58-75 (1990)]
Author(s): Ian P. Macfarlane, A. H. J. Fleming, Steve Iskra, Greg Haack
File Type: Journal Paper
Issue:Volume: 5      Number: 2      Year: 1990
Download Link:Click here to download PDF     File Size: 849 KB

Title: ADAPTING THE NUMERICAL ELECTROMAGNETICS CODE TO RUN IN PARALLEL ON A NETWORK OF TRANSPUTERS
Abstract: The Numerical Electromagnetics Code (NEC) has been adapted to run in parallel on a 16 transputer PARSYTEC machine. The modification of the code involved the manipulation of the Fortran source code and the development of parallel algorithms to fill and factor the matrix. The performance of the parallel NEC improved as the number of segments used in the simulation increased. When simulating a model with 300 segments the time taken was 45 seconds which is 13.3 times faster than using one processor. [Vol. 5, No. 2, pp. 76-86 (1990)]
Author(s): D. C. Nitch, A. P. C. Fourie
File Type: Journal Paper
Issue:Volume: 5      Number: 2      Year: 1990
Download Link:Click here to download PDF     File Size: 517 KB

Title: THE APPLICATION OF NESTED DISSECTION TO THE SOLUTION OF A 2.5D ELECTROMAGNETIC PROBLEM
Abstract: We use the method of nested dissection to solve a 2.5D finite difference electromagnetic problem. This method is considered in some detail, and we have found that the expected theoretical run time savings over more common methods are realised in practice. The program has been used to model EM propagation in coal seams with a view to detecting seam disruptions, which can cause a loss of production in longwall mining operations. Various experimental results and a field survey are discussed and we are able to use these results to construct a physically reasonable model which explains the field data. Some further realistics geological structures are modelled and a comparison between our modelling program and several independent methods shows satisfactory agreement.
Author(s): G. H. Smith, P. R. Williamson, K. Vozoff
File Type: Journal Paper
Issue:Volume: 5      Number: 2      Year: 1990
Download Link:Click here to download PDF     File Size: 1916 KB