The Eve' s-Knight computer simulation program records the losses within the rectenna element, divided up into approximately twenty locations. It computes harmonic coefficients up to the fifth harmonic in a Fourier analysis of five different wave forms. It prints out several key currents and voltages as a function of time. The complete description of the Eves-Knight math-modeling and computer simulation program and one example of its use and print out of data is shown in Appendix A. In the remainder of this section a brief introduction to the modeling and some typical results of the computer simulation will be presented. The results of the computer simulation will then be compared with the experimental data obtained from the ground plane test set up. 2.3.2 Mathematical Model of the Rectenna Element The electrical schematic model of the rectenna element in its simplest form is shown in Figure 1-11. The element is seen to consist of halfwave dipole antenna, a two section low-pass filter, and a rectification circuit consisting of a Schottky-bar rier diode in shunt across the circuit, an inductive section of line to resonate with the diode capacitance, and a capacitance to store energy and to remove harmonic content in the DC output power. The dipole antenna is matched to space, and the characteristic impedance of the filter is matched to the terminal impedance of the dipole. The input low pass filter, in addition to attenuating harmonic power, also acts as a buffer between the sinusoidally periodic input and the abrupt switching action of the diode. This simplistic model is not at all adequate for a computer simulation program. The behavior of the diode needs to be modeled in great detail. The sections of transmission line which are a portion of the low pass filter need to be broken down into short sections so that the lumped-network equivalent of these sections will suitably handle the higher harmonic currents which will flow in the filter sections. The computer simulation program is completely in the time-domain. The manner in which this is done, the number of divisions made, and the assignment of values of R, L and C to these divisions is clearly explained in Appendix A. 2. 3.3 A Representative Set of Data Resulting from the Use of the Computer Simulation Program Figure 2-11 represents a simplified schematic of the circuit elements of the mathematical model for the computer simulation program presented in Appendix A. The chief purpose of Figure 2-11 is to indicate the current and voltage parameters which are presented as a function of time during the rf cycle in Figures 2-12 and 2-13 respectively. The particular set of data corresponds to the test arrangement for the RXCV circuit element and diode on the ground-plane test fixture. The de power output level is 2.969 watts and the load resistance is 80 ohms - the value usually used for tests in the ground-plane test fixture. The complete set of data is given in Appendix A together with the graphs replotted in this section as Figures 2-12 and 2-13.
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