Multiplexer with constant or equal ripple Group Delay

I am designing four channells multiplexer 1.5 to 2.5 Ghz with constant or equal ripple group delay for the mux or each channell. I mean no problem for the channell to have diffrent group delay as long as it is constant in the its band
any idea or toplology will be appriciated
Cheers :sm7:

Look at the Matthaei's book ("Microwave filers,..."): sec. 4.05 - 4.08 and Charter 16.
May be it'll useful for you.