2. OPTIMIZATION OF THE MATCHING CIRCUIT The circuit elements, Cm and L in Fig. 1, are optimized for the better conversion efficiency in this section. Figure 3 shows that the theoretical mismatch loss is quite large, as much as about 20% when the efficiency is maximum. The values of L and Cm, matching circuit elements, are varied in order to reduce the mismatch loss. The optimum values of L and Cm when the conduction loss is neglected are about 4 nH and 4.2 pF, respectively. But in fact, the conduction loss of the lines is about 5% and cannot be neglected in order to optimize the efficiency. Figure 5(a) shows the efficiency and the losses vs the value of L when Cm is kept at 4.2 pF and the conduction loss of the lines are taken into account. When L is 2 nH, the efficiency becomes maximum and the mismatch loss becomes minimum. Next, when L is 2 nH and the value of Cm is varied, the results are shown in Fig. 5(b). The maximum efficiency is about 60% when Cm is 1.5 pF and the minimum mismatch loss is about 10%. Figure 6 shows the efficiency and the losses when the matching circuit is optimized; the optimum values of L and Cm are 2 nH and 1.5 pF, respectively. Compared with the nonoptimized case in Fig. 3, the efficiency increases by about 10% and the mismatch loss decreases by about 10%. CONCLUSIONS In this paper, a rectenna element is represented by an equivalent circuit taking account of the conduction losses of the lines, and the detailed distributions of the losses are investigated theoretically. As a result, we can improve the conversion efficiency by about 10% by optimizing the matching circuits. REFERENCES 1. Y. Anand and W.J. Moroney, Microwave Mixer and Detector Diodes, Proc. IEEE 59(8), 1182-1190, August 1971. 2. D.A. Daly, S.P. Knight, M. Caulton and R. Ekholdt, Lumped Elements in Microwave Integrated Circuits, IEEE Irans. Microwave Theory Tech. MTT-15(12), 713-721, December 1967. 3. R J. Gutmann and J.M. Borrego, Power Combining in an Array of Microwave Power Rectifiers, IEEE Trans. Microwave Theory Tech. MTT-27(12), 958-968, December 1979. 4. T.R. McCalla, Introduction to Numerical Methods and FORTRAN Programming. John Wiley, New York, 1967. 5. J J. Nahas, Modeling and Computer Simulation of a Microwave-to-dc Energy Conversion Element, IEEE Trans. Microwave Theory Tech. MTT-23G2), 1030-1035, December 1975. 6. Y. Shimanuki and S. Adachi, Theoretical and Experimental Study on Rectenna Array for Microwave Power Transmission, Trans. IECE Japan (B) J67-B( 11), 1301-1308, 1984.
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