Coherent signal-subspace transformation beam former

A family of coherent signal-subspace transformation (CST) preprocessors for improving the performance of beam formers is presented. The proposed beam former includes a CST preprocessor followed by a frequency-independent nulling procedure. If the exact CST preprocessor is used, it is shown that the steering and nulling responses of the CST beam former become frequency independent. This CST beam former is also interpreted as a wideband minimum-variance distortionless response (MVDR) beam former for minimising the total interference and noise powers. Several classes of the CST matrix are proposed and discussed. Unlike the traditional linearly constrained beam formers, the CST beam former effectively nulls the narrowband and wideband correlated interference(s). Simulation results show that even low-order approximate CST preprocessors substantially improve the nulling and the steering bandwidth of general arrays.