HF Direction-of-Arrival Estimation Using Helicopter-Integrated Single-Antenna

A helicopter-mounted antenna is designed for high frequency (HF) direction-of-arrival (DOA) estimations using the rotating main rotor-blade. Different from traditional direction finding (DF) arrays, a single helicopter-based antenna is developed. Different from conventional single DF antennas requiring directional radiation patterns, the proposed antenna uses blade modulation with phase diversity of nondirectional radiation patterns. Stable reflection coefficients and radiation patterns are obtained based on the characteristic mode (CM) analysis when the main rotor-blade rotates from 0° to 75°. The metallic helicopter structure is used as a main radiator, where a combination of pure CMs is excited by feeding one of the front landing gears based on CM surface current distributions without adding additional metallic structures. Radiation pattern diversity is demonstrated by calculating correlation coefficients of amplitude and phase of complex radiation patterns. The HF DF performance of the helicopter-based single antenna is validated by Cramer-Rao bound (CRB) values and multiple signal classification (MUSIC) algorithm.