Very poor specs! What about bandwidth, directivity? What do you mean by "frequency effects"?
Very good specs you can get by using waveguide structure.
Look at the Pozar's("Microwave engineering") and Matthaei's("Microwave filters, impedance-matching networks...") books. These books are the best for such problems.
you can use lang coupler with fr4 microssrip line or wilkinson coupler.
for more information to design this coupler you can:
1- search throgh the google
2- download book "RF circuit design by:ludwic"