**5. Bandpass filter with diamond-shaped edge-coupled CSRR (EC-CSRR)**

Recently, a novel bandpass filter using diamond-shaped edge-coupled CSRR was proposed [13]. This section discusses the design methodology of single-stage and twostage bandpass filters with diamond-shaped EC-CSRR structures.

#### **5.1 Single-stage BPF with diamond-shaped CSRR**

The physical construction of CSRR is shown in **Figure 11**, where the upper orange part is conducting layer, and the light gray part is the substrate. The CSRR structure consists of two diamond-shaped split resonant rings with their openings opposite (face to face) to each other for tight coupling between them. As CSRRs are integrated *Analysis and Design of Miniaturized Substrate Integrated Waveguide CSRR Bandpass Filters… DOI: http://dx.doi.org/10.5772/intechopen.104733*

**Figure 11.** *Schematics of single-stage SIW BPF.*

with SIW, a passband with an evanescent resonant mode lower than the SIW's cutoff frequency is created, miniaturizing the size of the conventional SIW [13]. **Figure 11** shows the dimensional view of a single-stage SIW filter loaded with diamond-shaped CSRR. The optimized dimensions of filter are: length of single-stage SIW LSIW = 10 mm, width of SIW WSIW = 8.5 mm, the inner radius of ring R1 = 1.0 mm, the outer radius of ring R2 = 1.6 mm, the thickness of ring T = 0.25 mm, the gap between open ends of outer ring G = 0.40 mm, the perpendicular distance between outer rings S = 1.25 mm. **Figure 12** shows the frequency response of single-stage CSRR incorporating SIW filter. The figure shows that in a single-stage SIW filter, one passband is formed with a center frequency of 8.75 GHz, below the waveguide cutoff frequency causing miniaturization by approximately 33%. The passband has 3-dB bandwidth of 0.42 GHz with an in-band insertion loss of 0.62 dB. The maximum value of return loss is 24.4 dB. Also, the stopband created has a high rejection level at the upper stopband.

**Figure 12.** *Frequency response of single-stage SIW BPF.*
