Novel rat‐race coupler of arbitrary power division design using resonant substrate integrated waveguide cavity

The contribution of this letter is to propose a novel rat‐race hybrid coupler of arbitrary power division design. The rat‐race coupler's arbitrary power division design is approached by using a resonant square substrate‐integrated waveguide (SIW) cavity. The employed SIW cavity is operated under the resonance of the combined TE102 and TE201 modes. Due to the nature of the square cavity, these two modes are termed degenerate modes which possess the same resonance frequencies but exhibit distinct field distributions. Theoretically, the cavity can be excited by an arbitrary combination of these two degenerate modes, and each of the modes' power is solitarily extracted by an SMA probe located at an adequate position. The microstrip together with the perpendicularly oriented slot are used to resonate the cavity with a designated combination of the degenerate modes. Sample experiments are conducted on 3 dB and 10 dB coupling designs with the circuits' performance evaluated by the coupling precision, isolations, and phase imbalances.