Analog envelop constrained filter with input uncertainty

Analog envelope constrained filtering problem with uncertain input (ECUI), we require the response of the filter to each signal in the input mask to lie within a prescribed output mask. The objective is to design the filter so as to minimize the noise enhancement whilst satisfying these constraints. The continuous-time ECUI problem was previously solved using filter structures which in practice were not physically realisable. This paper presents a new sub-optimal method which allows the use of more realistic filters, and which can converge to the optimal result provided a certain parameter is made small.