I would like to build a behavioral model for a Complex Filter.

I don't know the details of how to design a complex filter yet, but building a behavioral model might help get me there.

First let me say what I mean by a complex filter.
This is an analog filter with I and Q inputs designed to be driven by a quadrature down-converter. The complex filter attempts to pass one sideband (above or below the LO) while rejecting the other sideband essentially performing image rejection.

One way this filter is implemented is with two LPFs cross-coupled in such a way that the LPF response (viewed for positive and negative frequencies) is linearly shifted in frequency to create a bandpass response.

Can anyone provide guidance on how to design these filters or how to build behavioral models for them?

Thanks in advance,
John