HF Band Shipboard Antenna Design Using Characteristic Modes

The large wavelength of decameter wave brings a lot of practical difficulties to the design of shipboard antennas in high-frequency (HF) band. How to design conformal or even platform-embedded HF antennas raises us a new challenging topic. This paper proposes an approach to address such challenging problem through the combination of the characteristic mode (CM) theory with the structural antenna concept. 1) The CMs are solved to understand the resonant behavior of the ship platform. 2) We synthesize the radiating currents for designated radiation pattern by making use of the CMs of the ship platform. It allows the dominant radiating currents to locally distribute on the superstructure of the ship. Consequently, the superstructure becomes the main radiator. The modal solutions in CM theory ensure the efficiency of the synthesis procedure. 3) Nonprotruding slits are proposed to excite the synthesized currents. As the resultant HF shipboard antenna has no protruding elements around the ship, this design can be considered as either platform-conformal or platform-embedded. As an example, HF antenna on a realistic ship with broadside radiation pattern is designed. Simulation and experimental results on a 1:400 scale model demonstrate the effectiveness of the proposed approach in HF shipboard antenna designs.