| This thesis examines a novel approach to improving confidence levels in wire-grid models as well as a unique method of gaining insight into HF assessment parameters. This thesis is based on the Cormorant Search and Rescue helicopter. The helicopter is represented with a wire-grid model and solved with the well-known Numerical Electromagnetic Code (NEC-2) thin wire antenna code. The wire-grid model is verified against the customary wire-grid modelling guidelines that normally ensure confidence in the resulting radiation patterns. However, no measured radiation patterns are available as a validation of the computed patterns.; The starting point is a "benchmark" problem for which measured data is available, in this case a cylinder excited by a ¼ wavelength monopole antenna. The cylinder geometry is distorted or "morphed" into the helicopter in many small steps. At each step, the wire-grid model is verified against the comprehensive wire-grid modelling guidelines. In the evolution from the benchmark model, each step is a slightly more complex model, adding features to move closer to the helicopter geometry. As structures are added, such as the nose, the tail and its rotor, the engine cowling, the sponsons and the main rotor, their effect on the radiation patterns across the HF frequency band is seen.; The evolution of the cylinder into the helicopter is presented as a computer movie, included on CD-ROM, showing the change in the geometry and the associated change in the radiation patterns and in the frequency dependence of the assessment parameter. |
