Experimental results of wide-bandwidth high-frequency adaptive array processing

The authors discuss a 3 km diameter sparse planar antenna array facility for wide-bandwidth (1 MHz) high-resolution (1°) spatial processing experimentation for high-frequency (4-30 MHz) sensor and communication systems. It is demonstrated that both interference and noise can be canceled across a 1-MHz band using adaptive array processing methods. It is found that, while the HF environment is essentially stable over short time intervals (64 ms), significant variations may occur over longer periods (1 min), and these variations may significantly impact the performance of conventional beamformers and constrained least-squares adaptive array algorithms. Robust techniques, including diagonal loading and a signal subspace projection based approach, were successfully applied to reduce the sensitivity of the adaptive array to both calibration errors and fluctuations in the HF channel. Adaptive sidelobe cancellation techniques were combined with matched filtering to detect spread-spectrum signals