We consider measures of richness in multipath wireless channels. We examine bounds on the dimensionality of spatially constrained wireless signals. We show that the continuous system-model bounds on dimensionality rely on an implicit model for noise. We consider dimensionality bounds where the noise model is made an explicit parameter. We show that the dimensionality of a spatially constrained field may be considered as a parameter for a virtual antenna model. We propose a simple antenna model which incorporates spatial dimensionality and relate this to the current point-like model used in MIMO channel models.