*2.1.5 Simulated response of double unit*

The simulated S-parameter response is given in **Figure 9**. From the simulated S-parameter response, the array of two DGS units provides a lowpass filtering response with 3 dB cutoff frequency *fc* = 3.1 GHz, attenuation pole, *fp* = 3.8 GHz, and passband insertion loss of 0.5 dB. This also provides good transition (sharpness factor = 33.2 dB/GHz) between the passband and stopband and wider attenuation characteristics compared to single hexagonal head dumbbell DGS. The 20 dB rejection band is 2.1 GHz.

*Filter Designs Based on Defected Ground Structures DOI: http://dx.doi.org/10.5772/intechopen.103065*

**Figure 8.** *Simulated S- parameter Response of two DGS units.*

**Figure 9.** *Layout of the LPF using an array of three DGS units.*

*2.1.6 Improvement of the filter response by triple DGS units*

The performance of the lowpass filter can be improved again by increasing the number of DGS units in the array. Here three DGS units are placed side by side in the ground plane under the high-low line, and all the DGS units have the same dimension. The dimensions of the filter structure are as follows: *a* = 2 mm, *b* = 3.8 mm, *g* = 0.2 mm, *W* = 1.92 mm, *W*<sup>1</sup> = 5.6 mm, *W*<sup>2</sup> = 11.8 mm, L = 2 mm. The layout of the proposed filter using three DGS units is shown in **Figure 10**.

#### *2.1.7 Simulated responses*

The S-parameter plot of the proposed filter using three DGS units is shown in **Figure 11**. From the response of the scattering parameters, it is observed that the array

**Figure 10.** *Layout of the LPF using an array of three DGS units.*

of three DGS units provides a lowpass filtering response with 3 dB cutoff frequency, *fc* = 2.5 GHz, attenuation pole, *fp* = 2.8 GHz, and passband insertion loss of 0.6 dB. The sharpness of the passband edge of the filter is high, about 84.3 dB/GHz. The 20 dB rejection bandwidth is 4.2 GHz.
