**5.3 Slow wave effect**

Based on the slow-wave effect, an excellent phase shifter is fabricated using a CSRR-loaded SIW, as shown in **Figure 35**. CSRR provides the slow-wave effect in the TE10 mode of SIW. The phase velocity reduction resulting from the slow-wave effect provides a phase shift [45]. By controlling the phase velocity and the physical length of the transmission line, different degrees of phase shift can be achieved. The CSRR-loaded SIW realizes a direct conversion between the fast wave and the slow wave, which makes the phase shifter integrate with other devices easily.

**Table 4** shows the performance parameter of the phase shifters following different technological approaches.

#### **Figure 33.**

*Proposed SIW controllable phase shifter (a) structure. (b) Biasing circuit of the NIP diodes [49].*

**W**

**Figure 34.** *The three operating states of the proposed phase shifter [50].*

**Figure 35.** *Proposed a slow-wave structure.*
