A 10 step, 10 dB Gaussian taper for the transmit array is given in figure 16. There are 36 DC-KF power converter tubes per subarray at the center of the antenna, decreasing in quantized steps down to four tubes per subarray at the edge to provide the 10 dB Gaussian taper. There will be a total of 101,552 tubes in the antenna, integrated into the subarrays as shown in figure 17. This particular configuration uses a 70 kw klystron tube; an alternative concept has a 50 kw klystron, which requires approximately 140,000 tubes. The number of tubes per subarray would then vary from 50 tubes at the center of the antenna to six tubes at the edge in order to provide the 10 dB illumination taper. The radiation pattern for the 10 dB taper, 1 km array (and cr= 10° RMS phase error, + 1 dB amplitude error, and 2% random failures) at the ground rectenna is shown in figure 18. The effect of the antenna errors is to produce a wider, lower intensity main beam with higher sidelobes. For the SPS sytem concept, only a portion of the main lobe will be collected; the sidelobe energy occupies a very large area at very low density levels and is not economically feasible to collect. The peak power densities are 23 milliwatts per square centimeter at the rectenna boresight, 1 milliwatt per square centimeter at the edge of the rectenna, and 0.08 milliwatt per square centimeter for the first sidelobe, o which is two orders of magnitude below the U.S. radiation standard of 10mW/cm . If there is a total failure within the phase control system (for example, the uplink pilot beam transmitter is shut off), the subarrays will no longer be phased together and the total beam will be defocused. As shown in figure 18, o the peak intensity of the beam drops to 0.003 mW/cm and the beam width greatly increases. This peak power density is significantly less than the USSR guideline indicated on figure 18. Consequently, this is a fail-safe feature of the phasing system. In addition, there are sensors near the rectenna to detect any large changes in incident power density; this information would immediately be transmitted to the antenna to cease operations. In addition to the sidelobe patterns near the rectenna, the far-sidelobe patterns have been calculated. There had been some concern about the radio
RkJQdWJsaXNoZXIy MTU5NjU0Mg==