Design of Dual-Polarized, Platform-Based HF Antennas Using the Characteristic Mode Theory

We present a systematic method for designing dual-polarized, platform-mounted, high-frequency (HF) antennas for near vertical incidence skywave (NVIS) applications. To overcome the bandwidth (BW) and efficiency limitations of electrically small antennas, the characteristic mode (CM) theory is used to exploit the metallic platform as the main radiator. Low-profile coupling elements are mounted on different locations of the platform to excite two orthogonal, horizontally polarized CMs. This way, dual-polarized operation is achieved with a high isolation and sufficiently wide BW. In the design process, several key practical issues are taken into account and their impacts on the performance of the antenna are examined carefully. These include the type and design of the coupling elements, the presence and type of the earth, and the non-idealities and power handling capability in the impedance matching network components. The simulation results of both a full-scale and a 1:50 scaled model of the proposed structure are presented. The scaled-model prototype was fabricated and characterized in the presence of a ground plane emulating the properties of real earth at the scaled frequency of operation. The measurement results show a good agreement with the simulations, demonstrating the efficacy of the proposed approach in designing dual-polarized, platform-based HF antennas.