“…Since substrate integrated waveguide (SIW) was proposed, it has attracted a large number of researchers to apply it to microwave and millimeter wave communication systems because of its high Q value, low loss, and easy processing and integration [1][2][3][4][5][6][7]. Its most common applications are filter design [8][9][10][11] and antenna design [12][13][14][15]. Different shapes of SIW cavities have been studied, such as rectangular [16][17][18], circular [19][20][21], and triangular [22][23][24].…”