Top-loaded 60:1 Wideband Direction-Finding Sensor

Abstract

A wideband, four element array is designed to create suitable radiation patterns for angle of arrival estimation over a field of view of 0° to 80° in elevation and 360° in azimuth, using the Cramer-Rao Lower Bound (CRLB) as the figure of merit. The antenna elements are truncated monocones over a circular ground plane and operate over 100 MHz to 6 GHz. A study of the antenna geometry was performed to meet size constraints while minimizing the reflection losses at the input for frequencies up to 1 GHz. A method is presented to find the ideal loading impedance required for each frequency using multiport S-parameters derived from field simulations. The loading improves the maximum return loss from 0.4 dB to 6 dB. The study reveals a trade-off between minimal reflection losses and direction finding (DF) performance evaluated using the CRLB over the operating frequency. For the best investigated geometry using top loading the maximum root mean square error of the azimuth DF estimate remains below 13°.