Forward-based Receiver Augmentation for OTHR

An experimental multi-static HF radar is described that augments conventional over-the-horizon radar (OTHR) by placing multiple forward-based receiver systems within line-of-sight of targets of interest. With sufficient and appropriately located forward-based receiver sites the radar can generate target tracks that are independent of the uncertain ionospheric state and the system has low incremental cost compared with a complete OTHR. Each site in the multi-static system consists of a ten element linear array with a direct digital HF receiver per element architecture and the receiving components have sufficient dynamic range and spectral purity to operate in the footprint of the direct OTHR transmitter signal. The system uses custom receivers that integrate the frequency management function with the radar receiver function. Signal processing algorithms include real-time STAP and adaptive CFAR. Inter-site communications is achieved using a low-cost 802.11 b wireless communications network where the longest path in this network is 37 km. The system has performed beyond expectation for the desired target class.