###### Abstract  
In this work toward a sustainable operation of a self-powered wireless sensor, we investigated a multiband Wi-Fi/3G/4G/5G energy harvester based on a novel wideband circularly polarized antenna, a quadplexer, and rectifiers at four corresponding bands. This proposed antenna consisted of four sequentially rotated dual-dipoles, fed by a hybrid feeding network with equal amplitude and an incremental 90\({}^{\circ}\) phase delay. The feeding network was composed of three Wilkinson power dividers and Schiffman phase shifters. Based on the sequential rotation method, the antenna obtained a \(-10\) dB reflection coefficient bandwidth of 71.2% from 1.4 GHz to 2.95 GHz and a 3 dB axial ratio (AR) bandwidth of 63.6%, from 1.5 GHz to 2.9 GHz. In addition, this antenna gain was higher than 6 dBi in a wide bandwidth from 1.65 GHz to 2.8 GHz, whereas the peak gain was 9.9 dBi. The quad-band rectifier yielded the maximum AC-DC conversion efficiency of 1.8 GHz and was 60% at \(-1\) dBm input power, 2.1 GHz was 55% at 0 dBm, 2.45 GHz was 55% at \(-1\) dBm, and 2.6 GHz was 54% at 0.5 dBm, respectively. The maximum RF-DC conversion efficiency using the wideband circularly polarized antenna was 27%, 26%, 25.5%, and 27.5% at \(-6\) dBm of input power, respectively. circularly polarized antenna; Schiffman phase shifter; sequential rotation feeding network; ambient RF energy harvesting; self-powered wireless sensor +
Footnote †: journal: Sensors  
single-band rectenna is no longer suitable. In another approach to increase the efficiency and harvested power of rectennas, wideband antennas were used [6; 7]. This choice allows the rectennas to harvest more bands of RF waves. However, in some earlier works, due to the small gain and linear polarization of the patch [6] and monopole antennas [7], the harvesters only reached 18% and 8% of conversion efficiency at \(-5\) dBm, respectively. A recent approach using multiband antennas was presented in [8; 9; 10; 11]. Multiband energy harvesting can improve the amount of harvested energy. However, these works necessitate a huge load or achieve low conversion efficiency at a low-input power density. A dual-port patch rectenna in [8] required a high 5 k\(\Omega\) load and large size. The conversion efficiency was smaller than 5% at \(-10\) dBm in [9]. Circularly polarized (CP) rectennas have been used to increase the conversion efficiency because of their flexibility in electromagnetic transmission [12; 13; 14; 15]. At 2.45 GHz, a 75.6% RF-DC conversion efficiency was observed for 12 dBm input power [12]. The antenna had a narrow 3 dB axial ratio (AR) bandwidth. In addition, when the input power was reduced below \(-10\) dBm, it had low efficiency. A 2.45 GHz rectenna based on a slot antenna with a wider 3 dB AR bandwidth was presented in [13; 14]. At \(-6\) dBm, the efficiency can reach up to 59.5% and 59%, respectively. However, that rectenna can operate in just one single band; thus, it is difficult to supply self-powered wireless sensors due to the low power density of Wi-Fi. Therefore, the need for a circularly polarized, wide-band, high gain antenna to increase ambient RF energy harvesting efficiency and power has to be addressed. Recently, circularly polarized antennas have been made by using single feed [16; 17], dual feed [18; 19; 20; 21; 22], or a sequential phase feed (multiple-feeds) [23; 24; 25; 26; 27]. Using single feeds can reduce the design complexity, but they have narrow 3 dB AR bands [16] or low gain and radiation efficiency [17]. A wider bandwidth can be obtained using dual-band, dual-sense CP antennas or crossed dipoles using side parasitic elements [19; 20]. However, those antennas require large sizes and suffer from complicated designs. High gain and wide AR bandwidth are achieved by using a wideband quadrature coupler [21] or branch-line coupler [22] feeding to dipoles. Complicated designs and large sizes are some limitations to using an RF harvester.