A Spatially Confined, Platform-Based HF Direction Finding Array

A spatially confined, platform-based high-frequency (HF) antenna array with enhanced bandwidth and direction-finding (DF) accuracy is presented. As the HF band is widely used in many important civilian and military applications, HF DF systems are of great interest in electronic warfare support applications. However, due to the large wavelength, practical DF arrays mounted on moving platforms tend to be electrically small, resulting in fundamental limitations on antenna bandwidth and DF accuracy. Furthermore, many applications require mounting the array at a single location on the platform due to limited space and mobility considerations. To alleviate these issues, we employ the platform as the major radiator by exciting several of its significant characteristic modes (CMs) using a spatially confined antenna array. Specifically, we examined four DF array designs mounted on a representative, mid-size passenger airplane operating at 10 MHz in simulation, each of which is confined within a virtual sphere with a 3 m diameter. A scaled model of one design was fabricated and characterized. Cramer–Rao bounds and Monte Carlo test results are also reported. Our results demonstrate that the proposed DF array can provide a 15% lower direction-of-arrival estimation error than the theoretical limit of a standalone array possessing the same volume and having the same bandwidth.