Ionospheric Clutter Suppression in HFSWR Using Multilayer Crossed-Loop Antennas

Ionospheric clutter resulting from undesired radio signals reflected by the ionosphere severely deteriorates the detection performance of the high-frequency surface wave radar (HFSWR) in the mid- and low-latitude regions. To solve this problem, we propose a novel antenna configuration and method, i.e., using vertically placed, coaxial, multilayer crossed-loops as auxiliary antennas to cancel the clutter on the uppermost main crossed-loop (and/or monopole) antenna. The difference signals between the main and the auxiliary loops with the same normal direction are used as the reference signals in the adaptive filtering scheme to avoid cancellation of the wanted signals, i.e., the echoes horizontally coming from the sea surface. Both simulation and some preliminary experimental results are demonstrated to show the validity of the method.