An adaptive multiple-tap frequency domain digital filter processes an
input signal vector X from an plurality of spatially separated
transducers that detect energy from a plurality of sources including a
target energy source and at least one non-target energy source. The
filter receives and processes the input signal vector X to attenuate
noise from non-target sources and provides an output signal vector Y. Tap
weights W.sub.N for the filter are selected by first parameterizing each
of the tap weights W.sub.N, such that each of the tap weights W.sub.N is
characterized by a vector of parameters .beta..sub.opt, and the solving
for each parameter of the vector .beta..sub.opt by minimizing the
expected power of the array output signal Y. A robustness-control
transformation is then applied to the vector p to provide a robust vector
.beta..sub.opt wherein the robustness-control transformation identifies
and reduces target canceling components of the vector .beta..sub.opt
while preserving non-target canceling components. Finally, the weight
vector indicative of the filter tap weights is formed as a function of
the vector .beta..sub.opt. Notably, the present invention separates the
robustness constraining process from the beamforming power minimization,
in contrast to prior art techniques which combine the robustness
constraint into the beamforming power minimization. The present invention
uses a direct and flexible robustness control mechanism to yield a
beamformer that provides good performance and is robust to a wide variety
of adverse conditions.