In signal processing, a quadrature filter
is the analytic representation of the impulse response
An ideal quadrature filter cannot have a finite support.
It has single sided support, but by choosing the (analog) function
carefully, it is possible to design quadrature filters which are localized such that they can be approximated by means of functions of finite support.
A digital realization without feedback (FIR) has finite support.
This construction will simply assemble an analytic signal with a starting point to finally create a causal signal with finite energy.
This will impose an additional constraint on the filter.
the magnitude of the response of a quadrature filter equals the signal's amplitude A times the frequency function of the filter at frequency