advantage of phase control at the power module or tube level is a reduction in the antenna mechanical alignment (attitude control) and subarray alignment (antenna flatness) requirements (or a reduction in scattered microwave power if the same tilt requirements are maintained). There is also a reduction in the effects of distributed phase errors within the subarrays. The disadvantage is the increased cost due to the 94,000 additional pilot beam receivers and phase conjugation electronics. The present satellite antenna has 10 types of power modules as shown in Fig. 9 to provide a 10-step approximation to the 10 dB Gaussian illumination taper. The power modules range in size from 1.7388 x 1.7388 m at the center of the antenna to 5.2164 x 5.2164 m at the outer edge, where each mechanical subarray has four tubes or power modules. Since the power modules are now to be separately phased, each of the 10 types produces a grating lobe pattern determined by its dimensions, Sx and SY, as given by Eq. 15. The power modules are small in area compared to the subarrays and, hence, produce greater separation between the grating lobes. Some of the power module dimensions are integral multiples of smaller modules, e .g., the type-8 power module has dimensions 2.6028 by 5.2164 m which is one-half the size of the type-10 module at the edge of the antenna. Thus, grating lobes associated with different power module types may coincide. In the X direction, the first grating lobe of the type-8 module coincides with the second grating lobe of the type-10 modules. Equations similar to Eq. 28 for phase control to the subarray level could be written for each of the 10 types of power modules. These 10 individual patterns combine to form a composite pattern. Since the total transmitted power is divided between the module
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