Microstrip gapped square resonator

Hello,

Do you know a refference book or tutorial for designing microstrip square resonators (part of a BPF, with central frequency somewhere in the range 3...6 GHz) and evaluate coupling between them?
I will simulate the structure and tune it, but I need a starting point and approximate dimensions for the optimum microstrip width, square perimeter and gap spacing.
The square should be full wave or half wave?

Thanks

Check Topic 6

http://www.elec.cgu.edu.tw/~kschin/97%282%29%20Filter/