Fig. 1. Structure of the directional coupler designed in this paper

Fig. 2. Simulation results of the directional coupler in this paper

Fig. 3. Simulation results without DGS structure

Fig. 4. Simulation results with or without DGS structure isolation

Fig. 5. Simulation results of single branch + DGS structure

Fig. 6. Surface current distribution of the designed directional coupler

Fig. 7. Influence of the distance between two branches on the isolation

Fig. 8. The physical diagram of the directional coupler proposed in this paper

Fig. 9. Comparison of simulated and measured S parameters