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Millimeter Wave Energy Harvesting Using 4Í4 Microstrip Patch Antenna Array Ali Mavaddat, Seyyed Hossein Mohseni Armaki, Ali Reza Erfanian
Abstract—In this paper an energy harvester at 35GHz has been developed which known as rectenna. An array of rectangular microstrip patch antenna with 16 elements was used to efficiently convert RF to DC signal. A step impedance low pass filter is used between antenna and rectifier circuit to suppress second order harmonic generated by diode. A GaAs Schottky diode MA4E1317 was used in parallel with load as half wave rectifier circuit. The fabrication process is based on conventional optical photolithography to obtain an integrated circuit. The maximum RF to DC conversion efficiency of 67% was successfully achieved with input RF power of 7mW at 35.7GHz.
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I. INTRODUCTION
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Index Terms—Wireless power transmission, antenna array, energy harvesting, rectenna.
power transmission (WPT) is one of the primarily ideas that has been emerged in the history of communication technology. For this purpose, microwave power transmitted into the space will be collected by an antenna and is rectified with a diode, which known as a rectifying antenna (RECTENNA) [1]. There have been a lot of researches in ISM bands, 2.45 and 5.8GHz, including using antenna with different apertures, rectangular [2], ring [3], dipole [4], spiral [5], with linear [6] and circular [7] polarization, low pass [8] and band pass [9] filters, full wave rectifiers [10] and array structures[11]. Later the idea of WPT has grabbed considerable attention in scientific communities as a promising approach for powering satellites, power beaming from a space station to the earth [12], power beaming from a nuclear plant in space, power beaming from a moon based station [13] and powering highaltitude flying platforms [14]. Since weight and size would be crucial in these applications, they have been investigated by increasing the operating frequency. Increasing the frequency affect the size of designed rectennas in one hand(more applications) and reducing the RF to DC power conversion efficiency in another (leads to poor efficient Schottky diode and equipment in millimeter wave range). There have been some researches at 35GHz and 94GHz frequencies [15], [16], IRELESS
[17], [18]. Designed rectennas at 35GHz have already earned 72% RF to DC power conversion efficiency [13]. One of the key approaches to achieve high efficiency is increasing RF input power to the diode by using an antenna with high gain [18] or an array of antenna [19]. At lower frequencies by considering numerous available sources, applying an array could reduce the power harvested by antenna (narrower beam width). In contrast due to lack of millimeter wave sources, array structure would help the efficiency by focusing the beam toward transmitter antenna. In this work an array of microstrip rectangular patch antenna with 16 elements is used to collect high level of RF power, a step impedance low pass filter has been used to suppress second order harmonic generated by the rectifier diode and a GaAs Schottky diode is mounted in parallel to the load resistance. For fabrication the conventional method of optical photolithography was performed on a RT/Duroid 5880 with a thickness of 254µm, dielectric constant of 2.2 and loss tangent of 0.0009. Simulations and measurements have been conducted in each case to verify the performance of the designed rectenna.
This paragraph of the first footnote will contain the date on which you submitted your paper for review. The Authors are with the Electrical Engineering Department, University of MalekAshtar, Tehran, IRAN (e-mail:
[email protected]).
II. RECTENNA DESIGN
A. Antenna Simulation results of a single patch, 2×2 and 4×4 antenna array show that the HPBW varies of 74° to 39° and 18°. Also the antenna size would be changed from 2.5×3.3mm², 8.9×9.8mm² and 21.7×22.6mm², respectively. Narrower beam width will cost large areas which affect the application of the rectenna. It also makes the alignment between transmitter and receiver more difficult. At this point a 4×4 antenna array has been proposed. To design a 4Í4 antenna array which each element has been feeding by its non-radiating edge, first the single element and 2Í2 array have designed and modified by the help of CST Microwave Studio and HFSS simulators. In some previous literatures the space between every two elements has been recommended to be between 0.75Íλ0 to 0.85Íλ0 in order to get maximum gain [15]. Besides, to keep the side lobe levels in the minimum range, the distance of 0.75Íλ0was chosen in both x and y direction in proposed design. Fig. 1 shows the layout of antenna array and Table I includes the dimensions. The radiation pattern of 4Í4 antenna array has been simulated in two planes of φ=0° and φ=90°. The results have been showed in forms of co and cross polarization in Fig. 2. The maximum gain of 19dBi has been verified in both simulators.
2 The array was designed to have the input impedance of 50Ω. Fig. 3 shows the return loss of realized antenna. Simulated and measured results have a good agreement. It can be seen that return loss is lower than -32dB at 34.8GHz.
Fig. 3. Return loss of antenna array.
Fig. 1. 4Í4 patch antenna array layout.
W7 0.215 L7 3.486
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W 3.338 L 2.496
TableI Dimensions of Antenna Array (mm) W1 W2 W3 W4 W5 W6 0.183 0.5 0.205 0.498 0.215 0.498 L1 L2 L3 L4 L5 L6 3.04 1.825 2.595 1.746 4.331 2.44
B. Antenna + LPF To suppress the second harmonic generated by rectifier diode and avoid from reradiating by antenna, a step impedance imp low pass filter with 5 steps was designed and simulated with attenuation of -0.27dB and -20dB 20dB in 35 and 70GHz, respectively. The layout and simulated results have been presented in Fig.. 4 and 5. The high and low impedance were chosen to be 130Ω and 40Ω, respectively. This filter helps to maintain the efficiency of antenna array in maximum. In the next step, antenna array and LPF were built together on the same substrate used before. In order to decrease the effect of surface waves on the radiation pattern of antenna, the distance between antenna array and LPF was designed to be about λ0. Fig. 6 shows the simulated and measured return loss of antenna with LPF. It can be observed that the minimum return loss is obtained at 35.2GHz with tthe level of -18dB. The discrepancy between the simulated and measured results can be attributed to fabrication tolerances, connector loss and multiple reflections. It should be noted that antenna, LPF and soldered connector are connected together. The successive suc reflections between them create other resonance frequencies which affect the curve of measured return loss.
Fig. 4. Stepped- impedance LPF layout (dimensions in micrometer). (a)
Fig. 5. S-parameter parameter of LPF simulated by CST and HFSS.
(b) Fig. 2. Normalized simulated radiation pattern of 4Í44 patch antenna array array: (a) phi=0° (b) phi=90°.
Fig. 6. Return loss of antenna array + LPF.
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C. Rectifier circuit Half power rectifiers have been applied frequently in rectenna structures for rectifying RF power. In this work a GaAs Schottky diode MA4E1317 by M/A COM was used in parallel to antenna and load. The diode has a series resistance of 4Ω, zero-bias junction capacitance of 0.02pF, forward voltage of 0.7V and breakdown voltage of 7V. An analytical model proposed in [15] was applied to calculate the input impedance of diode. The equivalent circuit is shown in Fig .7
maximum efficiency region [21]. Since the rectenna is located in the vicinity of near-field, plane wave analytical equations are invalid for calculating harvested RF power. So, the delivered RF power was measured experimentally by using setup in Fig. 9(b). In this measurement, Antenna and LPF (without diode) were placed in the same distance which maximum output DC voltage recorded before and RF output power was measured with a HP spectrum analyzer. RF to DC conversion efficiency of designed rectenna was calculated by (1):
h RFtoDC =
Fig. 7. Equivalent circuit of schottky diode.
The RF input power should be high enough to turn on the diode properly. Besides, increase in RF input power will result in increase in amplitude of higher order harmonics. In this case, equations for input impedance of diode will not be satisfied. For this purpose the maximum RF input power was 2
(1)
Where is the measured output DC voltage on the load resistance and is the measured RF power delivered to the diode by setup in Fig. 9(b). Proposed design offers maximum achievable RF to DC power conversion efficiency of 67% with the RF input power of 7mW and the load resistance of 1kΩ at 35.7GHz. The change in efficiency over RF input power is plotted in Fig. 11. There is some discrepancy between the simulated and measured results particularly at the low input power. Three reasons can explain these differences: - Lack of accurate diode model at low input power (un estimating some intrinsic components of diode including , , and ). - Power loss due to mismatch between antenna and rectifier circuit. - Fabrication imperfections. The results from this work among other designs at 35GHz have been summarized in table II. As indicated the proposed rectenna features a high efficiency in low power applications.
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proposed to be less than 4 [15]. In this work output power and voltage of 10mW and 3V were chosen respectively. For a load resistance of 1kΩ, the input impedance of 242-j315 ohm was calculated for diode at 35GHz. A single stub was used to match the input impedance of diode to a 50Ω line.
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III. EXPERIMENTAL RESULTS
A. Output DC Voltage A photograph of the fabricated rectenna has been illustrated in Fig. 8. A line is attached to the center of non-radiating edge of one of elements as an output DC line. Since the peak of electromagnetic wave is zero at the center of a rectangular patch, the line could also act as a DC-pass filter. The disturbance of adding a line on performance of antenna was minimized by reducing the width of line to 60µm. Setup in Fig. 9(a) was used to measure the output DC voltage of rectenna. In this test, the RF power generated by a 20dBm Agilent microwave power generator, radiated from a horn antenna with the gain of 22dBi into the space. The distance between transmitter antenna and designed rectenna was swept in order to earn maximum output DC voltage. Since the RF output power of signal generator is limited, all measurements were taken in near-field. The output voltage was measured in four different distances from transmitter antenna (1, 8, 50 and 100mm) and has been presented in Fig 10. The maximum voltage of 2.18V was gained at 35.7GHz with the load resistance of 1kΩ at the distance of 8mm from the horn antenna. B. RF to DC Power Conversion Efficiency The wave incident upon the antenna array better resembles a plane wave as d increases. However, due to limitations on available transmit power, smaller distances between the horn and the antenna are necessary to drive the diode into its
Fig. 8. Photograph of the fabricated rectenna.
Fig. 9. Experimental Setup for the measurement of: (a) output DC voltage and (b) RF power delivered to the diode.
4 Table II Summarized results from this work and other designs at 35GHz [13] [14] [15] [16] [17] Technology Antenna Load (Ω) Output DC Voltage (V) Efficiency (%) Size (mm×mm) Delivered power (mW)
[18]
Dielectric Board 1×2 -
Board and Mechanical Assembly Single -
Duroid
Duroid
Duroid
Single 100, 400 -
Single 100 -
1×2 200 1.73
CMOS 0.13µm Single 100 0.76
72 120×120 -
50 4m (diameter) 140kW
39 120
29 2.6×2.6 120
35 10×24 42
53 1×2.9 10
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Fig. 11. Measured RF to DC power conversion efficiency of designed rectenna at 35.7GHz in the distance of 8mm from Horn Antenna.
IV. CONCLUSION In this paper a 4Í4 microstrip patch antenna array was proposed in order to achieve highest amount of electromagnetic waves for the application of WPT. Simulation results showed the absolute gain of 19dBi. Measurements performed on array, show a maximum conversion efficiency of about 67% at the frequency of 35.7GHz. Since the measurements were performed in near-field, RF power delivered to the diode was measured directly by using antenna and LPF structure. The results demonstrate that the proposed rectenna is well suited for millimeter wave energy harvesting. REFERENCES [1] William C. Brown, “The history of wireless power transmission by radio waves ,” IEEE Trans. Microwave Theory Tech., vol. 32, no. 9, pp. 1230– 1242, Sep. 1984. [2] J. A. G. Akkermans, M. C. van Beurden, G. J. N. Doodeman, and H. J. Visser, “Analytical Models for Low-Power Rectenna Design,” IEEE Antennas Wireless Propag. Lett., vol. 4, pp. 187-190, 2005. [3] Yu-Jiun Ren and Kai Chang, “New 5.8-GHz circularly polarized retrodirective rectenna arrays for wireless power transmission,” IEEE Trans. Microwave Theory Tech, vol. 54, no. 7, pp. 2970-2976, July 2006.
4×4 1k 2.18 67 22×42 7
[4] Wen-Hua Tu, Shih-Hsun Hsu and Kai Chang, “Compact 5.8-GHz rectenna using stepped-impedance dipole antenna,” IEEE Antennas Wireless Propag. Lett., pp. 282-284, vol. 6, 2007. [5] Joseph A. Hagerty, Florian B. Helmbrecht, William H. McCalpin, Regan Zane and Zoya B. Popovic´, “Recycling ambient microwave energy with broad-band rectenna arrays,” IEEE Trans. Microwave Theory Tech., vol. 52, no. 3, pp. 1014-1024, March 2004. [6] James O. McSpadden, Lu Fan and Kai Chang, “Design and experiments of a high-conversion-efficiency 5.8-GHz rectenna,” IEEE Trans. Microwave Theory Tech., vol. 46, no. 12, pp. 2053-2060, Dec. 1998. [7] Tzong-Chee Yo, Chien-Ming Lee, Chen-Ming Hsu and Ching-Hsing Luo, “Compact circularly polarized rectenna with unbalanced circular slots,” IEEE Trans Antennas and Propag, vol. 56, no. 3, pp. 882-886, March 2008. [8] Ji-Yong Park, Sang-Min Hanand Tatsuo Itoh, “A rectenna design with harmonic-rejecting circular-sector antenna,” IEEE Antennas and Wireless Propag Lett., vol. 3, pp. 52-54, 2004. [9] Young-Ho Suh and Kai Chang, “A high-efficiency dual-frequency rectenna for 2.45- and 5.8-GHz wireless power transmission,” IEEE Trans. Microwave Theory Tech., vol. 50, no. 7, pp. 1784-1789, July 2002. [10] Yu-Jiun Ren and Kai Chang, “5.8-GHz circularly polarized dual-diode rectenna and rectenna array for microwave power transmission,” IEEE Trans. Microwave Theory Tech., vol. 54, no. 4, pp. 1495-1502, April 2006. [11] Naoki Shinohara and Hiroshi Matsumoto, “Experimental study of largerectenna array for microwave energy transmission,”IEEE Trans. Microwave Theory Tech., vol. 46, no. 3, pp. 261-268, March 1998. [12] Noam Lior, “Power from space,” Energy Conversion and Management, 42, pp. 1769-1805,2001. [13] Peter Koert and James T. Cha, “Millimeter wave technology for space power beaming,” IEEE Trans. Microwave Theory Tech., vol. 40. no. 6, pp. 1251-1258, June 1992. [14]Yosef Pinhasi, Iosef M. Yakover, Arie Lew Eichenbaum and Avraham Gover, “Efficient electrostatic-accelerator free-electron masers for atmospheric power beaming,” IEEE Trans. Plasma Science, vol. 24, no. 3, pp. 1050-1057, June 1996. [15] Tae-Whan Yoo and Kai Chang, “Theoretical and experimental development of 10 and 35 GHz rectennas,” IEEE Trans. Microwave Theory Tech., vol. 40. no. 6, pp.1259-1266, June 1992. [16] James O. McSpadden, Taewhan Yoo and Kai Chang, “Theoretical and experimental investigation of a rectenna element for microwave power transmission,” IEEE Trans. Microwave Theory Tech., vol. 40, no. 12, pp. 2359-2366, Dec.1992. [17] Y.-J. Ren, M.-Y. Li and K. Chang, “35GHz rectifying antenna for wireless power transmission,”Electronic Lett., vol. 43, no. 11, 24th may 2007. [18] Hwann-Kaeo Chiou, and I.-Shan Chen, “High-efficiency dual-band onchip rectenna for 35- and 94-GHz wireless power transmission in 0.13µm CMOS technology,” IEEE Trans. Microwave Theory Tech., vol. 58, no. 12, pp. 3598-3606, Dec. 2010. [19] Ugur Olgun, Chi-Chih Chen and John L. Volakis, “Investigation of Rectenna Array ConFigurations for Enhanced RF Power Harvesting,” IEEE Antennas Wireless Propag. Lett., vol. 10, pp. 262-265, 2011. [20] R. Garg, P. Bhartia, I. Bahl and A. Ittipiboon, “Microstrip antenna design handbook,”Artech House, Boston, London, 2000. [21] Berndie Strassner and Kai Chang, “Highly efficient C-band circularly polarized rectifying antenna array for wireless microwave power transmission,” IEEE Trans Antennas and Propag, vol. 51, no. 6, pp. 1347-1356,June 2003.
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Fig. 10. Measured output DC voltage of designed rectenna.
This work Duroid
