**6.2 Two-stage BPF with BC-CSRR unit cell**

**Figure 19** depicts the proposed two-stage BC-CSRR BPF with separation between rings (*l*<sup>d</sup> = 7 mm).

#### **Figure 17.**

*Structure of the proposed SIW BC-CSRR unit cell [14]. (a) Top view; and (b) bottom view. w: Width of SIW, ds: distance between consecutive vias, dr: diameter of via, t: spacing between rings, s: thickness of microstrip line, l: distance of ring edge from SIW edge.*

**Figure 18.**

*Simulated frequency response of the original SIW and SIW BC-CSRR pair [14] (with parameters h = 1 mm, g = 0.3 mm, b = 3.9 mm, d = 0.34 mm, w = 12 mm, t = 0.5 mm, s = 2.65 mm, ys = 1.5 mm, ws = 0.5 mm, l = 2.5 mm, dr = 1.2 mm, ds= 2.2 mm).*

#### **Figure 19.**

*Structure of the proposed SIW BC-CSRR unit cell [14]. (a) Top view; and (b) bottom view.*

**Figure 20** shows the photograph of the fabricated filter using a substrate with ɛr = 2.65 and a thickness of 1 mm. **Figure 21** compares the simulated and measured frequency response of the BPF. The measured center frequency and 3-dB bandwidths are 5.75 GHz and 0.32 GHz, respectively. The measured in-band return loss is below 12 dB. The dimension of the filter is 20 mm x 13 mm (0.38 x 0.25 λo2).

*Analysis and Design of Miniaturized Substrate Integrated Waveguide CSRR Bandpass Filters… DOI: http://dx.doi.org/10.5772/intechopen.104733*

#### **Figure 20.**

*Snapshot of the SIW BPF with BC-CSRR pairs [14].*

**Figure 21.** *Comparison of simulated and measured result [14].*
