power loss in the junction area. These are currently subjects of investigation at Raytheon under contract NAS3-19722 to Lewis Research Center. The results of a preliminary study of the impact of these variables upon the losses in the diode are summarized in Figures 9-9 and 9-10. 9. 3 TOPOLOGY OF RECTENNA CIRCUITS Both the efficiency and low radio frequency interference requirements make it necessary to incorporate a low-pass filter into the rectenna element. A further requirement is a design configuration which can eventually be directly incorporated into a printed circuit, stripline, or similar configuration. Such a configuration has long been the ultimate objective of rectenna development programs because of its light weight and low cost. A rectenna must be a two-level structure to achieve high efficiency. However, the second level is merely a reflecting surface which need not be physically coupled to the front surface. The front surface plane can then be used to: a. Absorb microwave power b. Rectify it c. Collect rectified power in dc collecting busses which carry the dc power to the edges of the rectenna section for collection into larger busses d. Prevent radiation of power at harmonic frequencies The use of the front plane for the first three of these functions was characteristic of several early experimental rectennas. However, these rectennas did not have filters which would prevent the reradiation of all power at harmonic frequencies. To prevent harmonic radiation it is necessary to insert a low-pass filter between the antenna element, which absorbs the power from space, and the rectifying element. This is shown schematically in Figure 9-H. In Figure 9-11, the large capacitance to the left of the dipole is placed a quarter wavelength from the dipole and therefore an infinite impedance is seen by the dipole terminals to its left. A low pass filter must be constructed with inductance and capacitance if the losses are to be minimized, and the resulting configuration is shown in Figure 9-4 for a single section. It also shows how a single diode could be incorporated
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