A Heuristic Study of the Bandwidth Potential of Electrically Small, Platform-Based Antennas at the HF Band

In this article, two primary bandwidth considerations for electrically small, platform-based antennas in the high-frequency (HF) band were analyzed: coupling element (CE) location and CE design. First, we analyzed an all-metallic cuboid platform with dimensions of 3.20 × 2.76 × 7.54 m
³
at 5 MHz. At this frequency, the isolated platform has one dominant characteristic mode. In this analysis, a variety of electrically small CE designs, each occupying a fixed hemispherical volume with a radius of 0.5 m, were considered. The bandwidth potential of each element was examined when mounted at different locations on the platform. This analysis was then extended to a more complex platform: the U.S. Marine Corps Assault Amphibious Vehicle (AAV). The CE type and placement were found to have a significant impact on the impedance bandwidth of the antenna. For both the cuboid and the AAV, the highest bandwidth was obtained when a capacitive CE, the spherical-cap monopole, was mounted at the corners of the platform. Though one mode is dominant, contributions of higher-order modes play a significant role in the obtained bandwidth. A scaled model of the cuboid platform and the spherical-cap monopole were fabricated and experimentally characterized. Measurement results were found to be in good agreement with simulations.