Figure 1

Example: relative positions of a sensor ({\mathbf{x}}_{{\mathit{S}}_{\mathit{j}}})and of a primary user({\mathbf{x}}_{{\mathit{P}}_{\mathit{i}}}). The angle θ_i,j is defined with respect to a common reference system (horizontal axis in the figure), while {\tilde{\theta }}_{i,j} is defined with respect to the orthogonal to the positive direction of the sensor array axis.