If further development is undertaken on diodes for low-power density applications it is recommended that the following items be examined: a) The reduction of the specific resistance (ohms per unit area) of the back contact. b) The increase of the back contact area. c) A decrease in the skin resistance of the surface of the substrate over which the microwave current flows to the back contact. d) An increase in the doping density of the substrate to decrease the spreading resistance and decrease the skin resistance. 6. Radiation of Harmonic Energy From the Rectenna Element A two section low pass filter is inserted between the half-wave dipole of the rectenna element and the rectification circuit to store energy between rectification periods and to reduce the radiation of harmonic energy from the dipole. It has been recognized that there is an opportunity to enhance this attenuation in the design of the two-plane rectenna construction, because the section of transmission line that connects one rectenna element with the next can be made a half-wavelength long at the second harmonic and provide an effective shorting out of second harmonic energy at the input terminals of the halfwave dipole. It is recognized that this would be a critical adjustment if full advantage were to be taken of it. This approach was investigated with mixed and uncertain results. As the technique was studied on the ground plane fixture, it was determined that the absorption of second harmonic energy into a matched 50 ohm load, which represented the input to the dipole terminals, could be reduced by another 3 0 dB by adjusting the length of this section. There was even a slight improvement in efficiency noted. However, when the same technique was later applied to the section of the two-plane construction that was built and evaluated, it was found that there could be a two to three percent drop in efficiency at a point of adjustment of the electrical length of this line extremely close to the one found optimum for the reduction of harmonic energy. In any event the maximum reduction in harmonic content was nominal. It was also found that an open circuited stub line resonant at the third harmonic could be added to the terminals of the dipole input and result in a reduction of third harmonic output energy from 40 dB to 55 dB. 7. The Development of a Design that is both Environmentally Sound and is Suited to Low Cost Speed Production The development of basic technology for the rectenna for the full scale satellite solar power station is quite well advanced, but the adaptation
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