Fig. 1. Porous coupling model

Fig. 2. Transmission coefficient of the directional coupler with two holes

Fig. 3. Structural diagram of cross coupler

Fig. 4. Directivity of the designed coupler with different dx and dz

Fig. 5. Simulation results of cross coupler

Fig. 6. E-field distribution of the coupler with two holes

Fig. 7. Photos of double hole directional coupler

Fig. 8. Cold test system

Fig. 9. Cold chamber test results

Fig. 10. Simulation results of four hole cross coupler