# Implications of Metamaterial on Ultra-Wide Band Microstrip Antenna Performance
## 4 Antennas Implemented with Metamaterials
### C-SRR and Ring Rotation  
Studying the arrangements of the SRR double-ring orientation with respect to each other will provide an insight on the effect of the ring orientation on antenna's performance. Thus, Inner ring rotation of the SRR effect is investigated. Inner ring rotation of 10\({}^{\circ}\), 3\({}^{\circ}\) and 17\({}^{\circ}\) is applied along either the row or the column configuration of the array. Figure 28 presents the antenna with SRR in case 1, where the rotation angles applied to the rows of the array. Case 2 displays the SRR arrangement along the column of the array. Figure 28 shows the return loss results with inner ring rotation, which results in a rejection or notched band from 3.91 GHz to 4.25 GHz for rotation along the row. On the other hand. Implementing ring rotation along the column resulted in a rejection bandwidth from 4.82 GHz to 5.6 GHz, as shown in Figure 29. Antenna's gain in case 1, case 2, is around 5 dB as displayed in Figure 30.  
Figure 28: Inner ring rotation for C-SRRs.  
Figure 26: Circular microstrip antenna with C-SRR on the back.  
Figure 27: S\({}_{11}\) for the fabricated antenna with C-SRR.  
The next step for applying rotated inner rings will utilize positive (clockwise) and negative (anti-clockwise) angles rotation as displayed in Figure 31. Three cases are studied: Case 1: inner ring rotations for 47\({}^{\circ}\), 33\({}^{\circ}\) and 10\({}^{\circ}\) are applied to the array's column on the back of the antenna. Such arrangement resulted in a rejection at three frequencies 4.8 GHz, 5.4 GHz and 7 GHz, Figure 32. In Case 2 negative angle rotation of \(-47^{\circ}\) is implemented on the upper row, and the other two rows have positive angle rotation of 33\({}^{\circ}\) and 10\({}^{\circ}\), respectively. This design has no rejection frequencies in its bandwidth, Figure 32. In Case 3 all SRRs are implemented with negative angles rotation of \(-47^{\circ}\), \(-33^{\circ}\) and \(-10^{\circ}\). Figure 32 shows two rejection frequencies at 4.8 GHz and 7.2 GHz. The three designs have an improved frequency bandwidth between 2.2 GHz to 9.8 GHz and a maximum gain around 5.3 dB, Figure 33.  
Figure 30: Maximum gain of the three antennas.  
Figure 29: S\({}_{11}\) for the antenna of shifted C-SRR and inner ring rotation horizontally and vertically.  
Figure 31: C–SRRs inner ring rotation for positive and negative angle.  
Figure 32: S\({}_{11}\) of C-SRRs inner ring rotation for positive and negative angles.  
Figure 33: Maximum gain of the antennas.  
The final C-SRR implementation is to study inner and outer ring rotation with positive/negative angles. Three cases are investigated with angle rotation of 7\({}^{\circ}\), 13\({}^{\circ}\) and 30\({}^{\circ}\) as illustrated in Figure 34. The three studied cases are as follows: Case 1: angles 7\({}^{\circ}\), 13\({}^{\circ}\) and 30\({}^{\circ}\) are applied the inner rings. In the scenario the antenna has two rejection frequencies at 4.8 GHz and 5.4 GHz, Figure 35. In Case 2 the same rotation angles 7\({}^{\circ}\), 13\({}^{\circ}\) and 30\({}^{\circ}\) are used for outer ring. In this case the antenna did not exhibit any rejection bands, Figure 35. For Case 3: negative angles -7\({}^{\circ}\), -13\({}^{\circ}\) and -30\({}^{\circ}\) are implemented on the outer rings, this implementation resulted in rejection bandwidth between 4.69 GHz to 5.44 GHz and a second rejection frequency at 7 GHz as depicted in Figure 35. The three design cases have an improved bandwidth from 2.2 GHz to 9.8 GHz. The antenna gain for the 3 cases is between 5.4 dB and 5.55 dB, as shown in Figure 36.  
The circular antenna, with rotated inner ring angles of 47\({}^{\circ}\), 33\({}^{\circ}\) and 10\({}^{\circ}\) is fabricated in the lab and displayed in Figure 37. The measurement shows that the antenna has frequency bandwidth between 3.4 GHz and 9.4 GHz as shown in Figure 38; with VSWR is less than 2 in its bandwidth range. The simulated bandwidth is wider than the measured one, but both results are in good agreement.