Electromagnetic modelling of a warship at high frequency

This paper describes research work performed in the pursuit of a Masters of Engineering Degree at the Royal Military College of Canada, Kingston, Ontario. Here a Canadian warship is electromagnetically modelled using the generic “Wire-Grid Modelling” technique. This technique models the electrical characteristics of the exterior of the ship as a grid of interconnected perfectly conducting thin wires. The HF antennas on the ship are likewise modelled as thin wires and excited by voltages at their feed region. The resulting currents on the segment elements of the model and the fields surrounding the warship are computed using the NEC(3) computer program. The computed radiation patterns and antenna input impedance are compared to measurements made on a 1/50th scale-model. Since the segment mesh of the model serves only to approximate the electrical characteristics of the warship, the challenge in designing the model is to place the segments in locations where they will best represent the currents which would result on the surface of the ship from a similar excilation. Earlier work performed at Concordia University dealing with aircraft modelling has shown that with care, wire-grid modelling can produce accurate antenna impedance and radiation pattern results. The work presented here is a logical extension of this earlier aircraft work. Although the antenna types modelled here included whip, twin whip, and fan antennas, this paper will focus on the whip antenna.