**4. SIW switch**

The working principle of the SIW switch is to control the transmission of waves in the needed SIW path by various control methods, mainly including electronic control switches, magnetic control switches, and mechanical switches. Because of the ease of integration and low cost, PIN diodes are used as tunable devices loading on the surface of SIW for most electronic control switches. There have been many examples of designing switches using the difference of characters in diode forward and reverse bias [32–35]. Magnetic control switches are mostly loaded with ferrite [36, 37]. The permeability of the
