Fig. 6. Experimental conversion efficiency versus incident power. EXPERIMENTS A rectenna array used in this experiment is shown in Fig. 3. The conversion circuit unit is shown in Fig. 4. The conversion unit was fabricated by means of connecting a diode on a thin film circuit fabricated by microwave integrated circuit technique. An array antenna is composed by arranging 69 dipole antenna elements above a reflecting plane. The filter and diode unit was connected to a center element of the array only. The remaining elements were terminated by the input impedance of the element antenna, about 100 fl resistance. The conversion efficiency of the rectenna array per unit element was measured by comparing the obtained DC power of one rectenna with the maximum available receiving RF power of each antenna element. The measured conversion efficiencies are shown in Fig. 5 and Fig. 6. The calculated values in Fig. 5 and Fig. 6 are the simulation results based on some parameters of the diode used in this experiment. CONCLUSION The rectenna array for microwave power transmission has been investigated theoretically and experimentally. The conversion efficiency to DC energy and the spurious radiation of harmonics generated by the rectenna have been theoretically clarified. The conversion efficiency was measured for the experimental rectenna array model, and was found to agree approximately with the theoretical prediction. REFERENCES 1. R.J. Gutmann and J.M. Borrego, Power Combining in an Array of Microwave Power Rectifiers, IEEE Trans. MTT 27, 958-968, 1979. 2. Y. Akiba, Y. Ogawa, and K. Ito, On a Rectenna Module for SPS Reception by Use of a Circular Microstrip Antenna, Tech. Rep. IECE Japan AP 83-55, 37-41, 1983. 3. M. Kanda, Analytical and Numerical Techniques for Analyzing an Electrically Short Dipole with a Nonlinear Load, IEEE Trans. AP 28, 71-78, 1980. 4. Y. Shimanuki and S. Adachi, Conversion Efficiency to DC Energy and Spurious Radiation of Harmonics from a Receiving Antenna for Microwave Power Transmission. Tech. Rep. IECE Japan, AP 83-88, 49-56, 1983.
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