# A New Low-Cost Compact Antenna for the 2.45 and 5.8 GHz ISM Bands
## 3 Parameters Study and Simulation Results
### Impact of Created Slots in Steps 3 and 4  
Figure 6 shows the various sub-steps involved in step 3 of the design. Step 3 consisted firstly (step 3-a) in modifying the upper part of the ground plane and maintaining the patch structure obtained in step 2, i.e., a radiating element with a circular ring slot with an outer radius R1 of 9 mm and a position such that L\({}_{\text{P2}}\) is 16 mm. Two identical circular ring-shaped slots are then inserted symmetrically into the central ring in step 3-b and step 3-c, respectively. Figure 7 shows the evolution of the S11 in the various sub-steps shown in Figure 6. Firstly, the S11 improves after modification of the ground plane, compared with step 2 of the design (\(-16.48\) dB vs. \(-13.76\) dB at 2.41 GHz and \(-27.96\) dB vs. \(-23.25\) dB at 6 GHz). Insertion of the ground plane slots, therefore, improved the reflection coefficient without allowing a frequency shift around the 6 GHz frequency. The circular rings, on the other hand, enabled this frequency shift, resulting in the desired second frequency being obtained at the end of step 3. The positive influence of the ground plane slots on the S11 detected in step 3 made it possible to insert further slots to create a crenelated shape in the upper part of the ground plane, as shown in Figure 8a. The final optimization phase shown in Figure 8b involved adding slots inside the central ring. The study of the S11 is presented in Figure 9. The S11 has been improved in the 5.8 GHz band with the addition of the patch slots. Compared with  
Figure 6: Sub-steps of the antenna design in step 3 with slots insertion on (**a**) the ground plane (step 3-a), (**b**) the upper part (step 3-b), and (**c**) the lower part (step 3-c) of the central ring of the radiating element. Figure 7: Simulated antenna reflection coefficient at different steps related to slot insertion on (step 3-a) the ground plane, (step 3-b) the upper part, (step 3-b), and the lower part (step 3-c) of the central ring of the radiating element. step 3, the added slots improved the antenna's S11 (\(-13.82\) dB vs. \(-12.79\) dB at 2.4 GHz and \(-29.73\) dB vs. \(-24.81\) dB at 5.8 GHz) and bandwidth by 14%. The improvement in antenna bandwidth can be justified by the shape and positioning of the slots. Indeed, these two parameters would have induced capacitive and inductive effects in the antenna, which would have increased its bandwidth. In summary, the adjustments made to the ground plane and feed line had less effect than the slots on the patch. In fact, the patch slots made it possible to obtain two adapted ISM band frequencies and then also had an impact on performance parameters such bandwidth, gain, and radiation efficiency. Notches and slots on the ground plane and feed line increased the degree of freedom of the antenna's performance parameters for optimization. The observed reflection performance at the various steps of antenna design and the symmetry of the antenna can be justified by analyzing the surface current distribution on the patch. Figure 10 shows the current distribution in the 2.45 GHz band at the various steps of antenna design. Gradual intensification of the patch current surface distribution, particularly around the slots, is noted. No current is obviously observed in the slots. This shows that the surface current bypasses the slots. This current distribution on the patch is symmetrical. This observed symmetry is explained so by the symmetry of the antenna itself. Gradual intensification and symmetrical current distribution are also observed at 5.8 GHz. Figure 8: Sub-steps from antenna design to step 4 with (**a**) the creation of a complete slot shape across the width of the ground plane at step 4-a and (**b**) the insertion of slots inside the central ring at step 4-b. Figure 9: Simulated antenna reflection coefficients at step 4 with, at step 4-a, the creation of a complete slot shape across the width of the ground plane and, at step 4-b, the insertion of slots inside the central ring.