  Complex signal detection in additive noise can be performed by a one-sample
bivariate location test. Spherical symmetry is assumed for the noise density as
well as closedness with respect to linear transformation. Therefore the noise
is assumed to have spherical distribution with $\alpha-$stable radial density.
In order to cope with this difficult setting the original sample is transformed
by Pade' methods giving rise to a new sample with universality properties. The
stability assumption is then reduced to the Gaussian one and it is proved that
a known van der Waerden type test, with optimal properties, based on the new
sample can be used. Furthermore a new test in the same class of optimal tests
is proposed which is more powerful that the van der Waerden type one.
