Wideband, Direction of Arrival Estimation Using Small-aperture Antenna Arrays

Book excerpt: The HF, VHF and UHF bands are widely used in many important civilian and military applications, direction finding (DF) systems covering these bands are of great interest in electronic warfare support applications. However, due to large wavelength in these frequency bands, practical antennas are usually electrically small and have limited bandwidth, especially when they are deployed on moving platforms with very limited space to accommodate them. What's worse, the small aperture also set a physical limitation on the accuracy of direction of arrival (DoA) estimation. This dissertation investigates four approaches to develop small-aperture antenna arrays with enhanced bandwidth and DoA estimation accuracy. The first approach focuses on optimizing the antenna structure and array geometry. I examined different array topologies and adopted the one that provides the lowest Cramer-Rao bound (CRB) and both azimuth and elevation DoA capability, and then, further optimize it to efficiently utilize an available volume. The second approach relies on selecting and exciting a group of the platform's characteristic modes (CMs) that provides the lowest CRB. The antennas are placed at multiple locations on the platform for the best excitation of the CMs. The third approach further brings the antennas to a single location on the platform. Multiple CMs can still be excited and enable the spatically-confined array to achieve DF accuracy better than the theoretical limit of standalone array. The last approach explores a compact, wideband array with multiple independent beams and vertical polarization that is suitable for both directional networking and DoA estimation applications. Finally, I discuss possible future works that are important to developing wideband, direction of arrival estimation systems using small-aperture antenna arrays.