Substrate integrated waveguide 3 dB directional coupler based on air-filled vias

摘要

A novel substrate integrated waveguide (SIW) 3 dB directional coupler based on air-filled vias (AFVs) is proposed and experimentally validated at Ka band. The AFV units can be used for tuning the effective permittivity by adjusting the dimensions of vias and period. Two rows of optimised AFVs are inserted in each branch of SIW directional coupler to cut off TE30 mode and achieve 3 dB coupling with 90° phase difference. A 90° phase shifter is designed based on the AFVs as well and the quarter wavelength impedance transformer is introduced. Finally, a 3 dB directional coupler prototype with 180° phase difference was designed and fabricated. The experimental results show that about 11.43% fractional bandwidth is obtained with a return loss of input port better than 19 dB, power equality within ±0.33 dB, isolation better than 25 dB and phase differences within 180° ± 10°. The agreements between simulations and measurements validate the design and it is a good candidate for millimetre-wave applications.