# A Compact Circular Rectenna for RF-Energy Harvesting at ISM Band
## 3 Rectenna Simulation Results and Discussion  
### Monopole Antenna Simulation Results and Discussion  
The proposed monopole CMCP antenna is simulated using CST software and parameters S(1,1), and Z(1,1), and parametric analysis is carried out at 2.45 GHz. Figure 6 depicts the S11 parameter of the simulated antenna. It shows that the return loss values are \(-28.7\) dB at 2.45 GHz and \(-19.5\) dB at 4.29 GHz. The impedance bandwidth of the prototype CMCP antenna is 2.94 GHz from 2.06-5.0 GHz, which includes ISM band (2.45 GHz), IMT services (3.5 GHz), WiMAX applications (3.3-3.8 GHz) and satellite communications (2-4 GHz). To understand the influence of the PGP on impedance matching and antenna performance, all the variables are kept constant, and for the different values of the PGP length simulation, the results are depicted in Figure 7.  
PGP length is varied from 11 mm to 14 mm and it is observed that there is a significant change in bandwidth and impedance matching. Increasing the length of the PGP from the initial value improves the impedance matching and bandwidth, and if the increasing continues, at the final value, both bandwidth and impedance matching decreases. At 12.5 mm of the PGP length, good impedance matching and wide bandwidth were observed. The wide bandwidth of 2.94 GHz from 2.06 GHz to 5.0 GHz, and the impedance of the designed CMCP antenna, which is 50 ohms at the optimal PGP length, is equal to  
Figure 6: Monopole CMCP antenna S(1,1) plot. Figure 7: (a) S1,1 and (b) Z1,1 results for different values of the PGP length. 12.5 mm. The monopole CMCP antenna is proposed for RF-energy harvesting in which the impedance of the receiving antenna plays a crucial role in designing the IMN, whereby more energy transformation takes place from the RF source to the rectifier with a minimum power loss, improving the PCE. The impedance of the proposed antenna at PGP length of 12.5 mm is analyzed for the real and imaginary parts of the impedance of the antenna and \(50.1+3.65\) is found from the graph depicted in Figure 8.  
The simulated radiation efficiency and realized gain of the designed monopole CMCP antenna against frequency are depicted in Figure 9. The radiation efficiency of the antenna is greater than 86% in the entire wideband, and at the resonating frequency 2.45 GHz, the radiation efficiency is 95.4%. The realized gain of the antenna is 2.38 dBi at 2.45 GHz. The polar plot of the E-plane and H-plane radiation patterns at 2.45 GHz for the CMCP antenna in co-polar and cross-polar are shown in Figure 10. In the E-plane, the cross-pole magnitude is 20 dB less than the co-pole magnitude, and similarly, for H-plane, the cross-pole magnitude is 83 dB less than the co-pole magnitude for 2.45 GHz. It is observed that at a resonating frequency of 2.45 GHz, the radiation patterns are approximately omnidirectional for co-pole and bidirectional for cross-pole, with very low magnitude. By studying the  
Figure 8: Z1,1 plot of the CMCP antenna at L\({}_{G}\) = 12.5 mm. Figure 9: Radiation efficiency and gain plot of the CMCP antenna. characteristics of the radiation patterns, the designed CMCP antenna radiates well in all directions with equal magnitude. The performance of the CMCP antenna in terms of return loss and maximum gain are calibrated by using E5071C ENA series VNA, Agilent technologies after standard one port SOL between 2.0 GHz to 5.0 GHz. Figure 11 depicts the measurement setup and the comparison of simulated and calibrated S\({}_{11}\) results of the CMCP antenna. From the plot, it is observed that calibrated results are more correlated with the simulated results. The resonant frequency of the calibrated results have moved slightly upward compared to the simulated kind which was generated unintentionally due to a manufacturing error, had a cable connector mismatch during calibration, and a manual soldering of the SMA connector.