grating lobe peak for the power tube level is 848 km from the rectenna with an amplitude of 0.011 relative to the first grating lobe peak associated with 10-m subarrays. This grating lobe pattern for phase controlling at the power tube level is expanded to encompass the continental United States as shown in Figure 3. For a rectenna location as shown for a mid-latitude, approximately 35 grating lobe peaks are incident upon the United States. Since this corresponds to only about 0.01% of the nation's land area, rectenna siting should be able to preclude any grating lobes incident upon an observatory. The microwave power density levels as a function of range from the rectenna are shown in Figure 4 for phase control at the tube level. An antenna -4 2 tilt of 1 arcmin produces grating lobe peaks of approximately 2 x 10 mW/cm in the United States. This level is almost two orders of magnitude below the 2 USSR guideline of 0.01 mW/cm . The variation in peak power density as a function of antenna tilt and phase control level is illustrated in Figure 5. The grating lobe peaks are improved (reduced) by phase controlling at the tube level rather than at the subarray level. If there is a problem in the attitude control system meeting the ± 1 arcmin pointing requirement, it is possible to FIGURE 3. Grating Lobe Pattern for Phase Control Down to Power Modules
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