Novel broadband design of SIW directional coupler

Abstract

To enable broadband characteristic, a novel type of directional coupler based on slot coupling theories is proposed. Besides, this directional coupler is designed on the basis of substrate integrated waveguide. Strong coupling directional couplers are proposed and simulated with different coupling degrees −3, −5, and −7 dB. From the simulated results, it illustrates that these couplers show low return loss under −20 dB and high isolation above 20 dB in the frequency of X band. The results also show good performances with ∼30.8% FBW for −3 dB (±0.3 dB) coupling degree, 29.9% FBW for −5 dB (±0.5 dB) coupling degree, and 36.8% FBW for −7 dB (±0.7 dB) coupling degree. It is easy to integrate in microwave and millimetre-wave integrated system because of the characteristics of planar form and compact size of SIW directional couplers.