# Compact Dual-Band Tapered Open-Ended Slot-Loop Antenna For Energy Harvesting Systems
## 1 Introduction  
With the great advancement in wireless communication technology and personal wireless communications, there is a constant demand for antennas with multi-functions. Multiband antennas that are simultaneously operating at different frequency band are preferred for several practical applications. For instance, wireless mobile services, satellite communication, biomedical diagnosis, and energy harvesting applications [1, 2]. The license-free Industrial-Scientific-Medical (ISM) frequency bands located at 0.9, 2.4, and 5.8 GHz are usually exploited to support wireless power transfer (WPT) technology. Currently, the RF energy transfer in ISM Bands is not only promising, but it also becomes a reality as some pioneer companies propose several full kits: Powercast Corporation, AnSem, and MicroChip, to name a few [3]. However, there is still a great demand to make the RF energy transfer an appropriate, low cost and easy-to-use solution to sufficiently powering the remote wireless nodes. One of the most critical points concerns the harvesting capability of the RF modules is the design of a compact, simple, dual-band, and lightweight antenna. At present, 0.92 and 2.45 GHz frequency bands are more attractive because of their good performances of data speed and anti-environment jam ability [4, 5]. The 0.92-2.45 GHz ISM bands are very common and widely used for different applications, like Radio-frequency Identification (RFID), local area networks, and many other wireless services, like Bluetooth. Therefore, the power that isemitted into the environment is adequately large when compared to other applications. This power can be recycled and utilized for energy harvesting [6; 7]. The antenna plays a key role in the harvesting of electromagnetic energy. It is used to harvest electromagnetic waves in space and transform them into electric currents to be processed further. Nevertheless, there are some challenges for developing an antenna to harvest power efficiently at both bands. For instance, the operation mode and frequency differences between 0.92 and 2.45 GHz are too large to properly achieve dual-band structures [8; 9; 10]. Owing to the greater demand for applications in these frequency bands, several attempts have been made with the purpose to design compact and an efficient antennas operating in these bands [11; 12; 13; 14; 15; 16; 17]. To meet the dual-band requirements, more recent evidences highlighted the design of a dual-band antenna. For instance, [PERSON] et. al introduced a wide band Yagi-Uda antenna to cover a wide band from 1.8-2.1 GHz. Although the proposed antenna can harvest the power from DCS-1800 and UMTS-2100, it does not cover 0.9 GHz [18]. A slot-loaded dual-band \(\lambda_{o}/2\) folded dipole antenna is reported in [19] to serve the energy harvesting system at 0.9/2.45 GHz. The folded dipole is utilized to shrink down the antenna size and operates at 0.9 GHz, whilst a slot is etched from the folded dipole to generate the second band at 2.45 GHz. Although the antenna has achieved a dual-band operation, it employs double-layer configuration. Dual-band electrically small antenna (ESA) operating at 934 MHz and 1.55 GHz is presented in [20]. The structure of this antenna is based on a loop that excites two different sizes of split-ring resonators to achieve dual resonant structure. Additionally, a compact planar dual-band antenna based on the monopole structure for UHF and ISM bands is reported in [21] with a large size. A dual-band antenna for energy harvesting application has been designed and investigated in [22] to operate at 1.95 and 2.45 GHz. The antenna has achieved a good enhancement in antenna gain. The measured results showed a gain of 8.3 and 7.8 dBi at 1.95 and 2.45 GHz, respectively. In [23], a dual-port triple-band L-probe microstrip patch rectenna design for ambient RF energy harvesting using the GSM900, GSM-1800, and UMTS-2100 bands is described.