The effect of interference power and bandwidth on space-time adaptive processing

In STAP, an N-length digital filter or tapped-delay line with adjustable weights is placed behind each antenna element. With L antenna elements and N taps per element, the STAP-equipped array has LN-1 degrees of freedom available. Theoretically, up to LN-1 independent. radio frequency interference (RFI) sources can be nulled, providing a significant advantage over a conventional adaptive array which is limited to L-1 spatial degrees of freedom. However, this is only obtained for RFI with 0% bandwidth. Wideband interference is known to limit adaptive array performance. The degrees of freedom consumed in STAP are shown to be strongly dependent on the interference power and bandwidth. We demonstrate that a strong direct path wideband RFI can consume more than "N" degrees of freedom in a multi-tap STAP wherein "wideband" is defined as a bandwidth equal to the sample rate or inverse tap delay of the STAP processor. Thus, the effect of a strong wideband RFI direct-path source on STAP performance can be similar to that of a dispersive multipath environment.