Numerical electromagnetic models of cube-shaped boxes an initial investigation for near-field prediction of HF shipboard environments

Abstract : An investigation was performed to evaluate the accuracy of numerical modeling of near fields for antennas on or near surfaces using the Numerical Electromagnetic Code (NEC). Average power gain and input impedance were calculated, for two models. The first, a dipole antenna located inside a cube- shaped wire grid box of 1 meter sides was evaluated for a wide range of frequencies in free space. The second, a monopole antenna mounted on the top of two cube shaped boxes (a wire grid and surface patch box) of 0.1 meter sides over a perfectly conducting ground was evaluated from 1 to 1.4 GHz. The monopole was positioned at the center, at an edge, and at the corner of the box top. For the dipole in the box, the average gain and input impedance are presented and evaluated. For the monopole on the box, calculated results are compared to measured admittance values. The NEC wire-grid model results compare closely to the measurements, but for surface-patch models, only one position of the monopole yielded satisfactory correlation to measurements. Recommendations for improved numerical modeling performance are made.