**2.1 Performance improvement of lowpass filter using hexagonal head dumbbell shaped DGS**

The hexagonal head dumbbell-shaped DGS is shown in **Figure 1**. The microstrip line is placed on the top plane and the proposed DGS on the ground plane. The different slot gaps, *g* = 0.2 mm, transverse slot length, *a* = 2 mm, *b* = 3.8 mm, a width of the 50 Ohm microstrip line, *W* = 1.92 mm.

### *2.1.1 Simulated results of unit cell*

The structure is simulated by IE3D [11, 13] simulation software, and the simulated result shows a one-pole Butterworth prototype response given in **Figure 2**. The cutoff frequency is obtained at 3.3 GHz, and the transmission zero frequency is obtained at 5.1 GHz with attenuation of 23.9 dB. The sharpness factor is 11.6 dB/GHz.
