A double layer crossed over Substrate Integrated Waveguide wide band directional coupler

Directional couplers are widely used in microwave or millimeter wave power splitters or antenna feeding circuits for generating desired power division ratio at a specified bandwidth. The bandwidth and size are the two key parameters in the specifications of couplers. A compact coupler could save space and reduce the metal loss, and also the wide band properties will bring a generalized usage of couplers. Rectangular waveguide directional couplers have been seriously investigated for a long time [1]-[3] and numbers of circuits or structures have been obtained to achieve high performance flat coupling properties. However, manufacturing such a coupler requires high accurate machining and thus results in high cost. Substrate Integrated Waveguide (SIW) is a dielectric filled waveguide structure that has the similar propagating modes as rectangular waveguide, but manufacturing of such a waveguide structure requires only the normal Print Circuit Board (PCB) process and results in the merit of low cost and mass production ability. SIW directional couplers also have been successfully designed and fabricated [4]-[5]. But most of the couplers are designed by H-plane wall of two adjacent SIW which is guided wavelength depended and requires large PCB area. Single layer SIW compact size crossed waveguide directional coupler also been mentioned [6], the bandwidth of the coupler is limited. This paper introduced a double layer wide band compact directional coupler with two SIWs crossed over each other. Large range of coupling coefficient and wide band characteristics are achieved. The coupling is realized by the cross slots between upper layer SIW and lower layer SIW. Structures and parameters, simulated and experiment results are presented. Such a coupler could be a good candidate in antenna feeding structure or power divider applications.