**3. SIW loaded with basic EC-CSRR structure**

A SIW bandpass filter based on edge-coupled CSRRs was proposed for the first time in 2007 by [11]. The SIW filter consisted of the tapered transition line with the CSRR. As SIW possesses high-pass characteristic, whereas a CSSR manifests bandstop characteristic, therefore by integrating CSRR with SIW, a bandpass SIW filter is designed. **Figure 6** depicts the structure of SIW with CSSR etched in the top side of the substrate.
