Designs for broad-band cavity-coupled microstrip directional couplers

Cavity-coupled designs for microstrip directional couplers are presented in this paper. Different coupling coefficients are pursued. All the designs feature a cavity in an electrically thick ground plane, which serves as a common ground for two back-to-back microstrip lines. These cavity-coupled designs can offer more bandwidth compared to their corresponding slot-coupled designs. Finite element method is chosen to carry out the required simulations for the proposed designs because of its accuracy. The validity of the simulation results is verified experimentally and good agreement is observed.