# Compact Dual-Band Tapered Open-Ended Slot-Loop Antenna For Energy Harvesting Systems
## 3 Experimental Results and Simulation  
The geometrical configuration of the proposed antenna has a simple, single layer and compact structure. The antenna uses a commercial cheap FR4-epoxy substrate with a thickness of 1.6 mm, a relative permittivity of 4.6, and a loss tangent of 0.02. The antenna has a profile size of \(32.5\times 53.5\) mm\({}^{2}\). The antenna is a planar type-based structure and its fabrication is very simple using either mechanical (CNC) or chemical (photolithography) techniques. The chosen approach in our case is the mechanical fabrication method, which provides a clean and high precise fabricated prototype. The fabrication is done using a mechanical etching process with a 100 \(\mu\)m resolution. The inner conductor of the input SMA connector is connected to the main strip of the loop, and the outer pin of the connector is directly soldered to the right side metal. The fabricated antenna is shown along with the S11 Figure 4a. The properties and performance of the proposed antenna are predicted and optimized through electromagnetic simulation software in the Ansoft HFSS environment. The measured return loss, as shown in Figure 4a, indicates clearly that the proposed antenna has a multiband characteristic. Two resonant frequencies are located at 0.92 GHz and 2.45 GHz, with the return losses exceeding 20 and 22 dB, respectively. When compared with the simulated results, the measured reflection coefficient achieves good agreement in both the resonant frequency and bandwidth. It is noted that the higher band resonant frequency is slightly shifted toward the lower frequency region. This is attributed  
Figure 4: Experimental performance of the proposed antenna, (**a**) input reflection coefficient over a wide bandwidth to emphasize the dual-band operation around 920 MHz and 2.4 GHz; (**b**) measured and simulated peak realized gain, the gain is calculated over the lower and higher band at the peak direction; and, (**c**) antenna radiation efficiency at the lower and higher band. to the dielectric constant fluctuation with frequency, and the parasitics that are produced form the connecting port. On the other side, the realized antenna gain is illustrated in Figure 4b. The gain is plotted for the lower band from 0.9 to 1 GHz, and extended from 2.2 to 2.6 GHz at the higher band. While the simulated peak antenna gain at 920 MHz is 2 dBi, the corresponding peak value at 2.4 GHz is 5 dBi. In contrast, the exact measured gain at the lower band is 1.8 dBi, while that at the higher band is 4.2 dBi. The gain was estimated at the end-fire antenna direction. It is apparent from the curves that both measured and simulated results are slightly matches. The slight mismatch between measurement and simulation results are not significant. This mismatch is due to the solder connection of the fabricated antenna that is not considered in the simulation. Furthermore, the resolution of CNC machines is another factor for this little bit mismatch. Although this little bit mismatch, the antenna still covers the proposed bandwidths. The most important antenna characteristic is the radiation pattern. The radiation pattern of the proposed antenna is experimentally tested and compared with the simulation results, as shown in Figure 5. The radiation pattern at the lower band resembles the conventional small loop antenna which is given like a figure of eight in the XY plane and omnidirectional in the XZ plane. In contrast, the directional end-fire radiation pattern is achieved at the higher band, because the ground plane acts as a reflector. Several metrics are compared against similar research work existing in literature to evaluate the benefits of the proposed design, as depicted in Table 1. The comparison reflects that the proposed antenna offers several merits in terms of compactness, gain, low cost and simple architecture. The proposed antenna provides a compact footprint as compared to the architecture introduced in [11; 12].