equation for ripple optimization goal

In designing filters, it would be nice to optimize to a minimum insertion loss ripple. i.e. S21 less than 0.5dB pp.

Does anyone know how to write that as an equation? I'm running AWR/Microwave Office.

thanks,
GE

"Minimal ripple" makes no sense. Filters can be either designed for no passband ripple (Butterworth, Bessel, Chebyshev II) or specific passband ripple amount (Chebyshev I, Elliptic).

The reason why you accept a specified ripple in some cases is that it's linked with a steeper transition band.