Design and tuning of wideband two-layer Substrate Integrated Waveguide directional couplers

In this paper, design process of several 20dB wideband coupler on the basis of SIW using modeling the coupler by distributed low-pass filter prototypes and using chebyshev coefficients for these prototypes have been done. The base of work is the Bethe coupling theory for small apertures that has been expanded for large apertures. The type of apertures for our designs includes circular, rectangular and square. Also a Riblet-Saad coupler has been designed and simulated. We also introduced a new method to calibrate aperture dimensions to obtain our desired coupling. Finally, a comparison between different types of couplers has been done.