antenna, so the machine doing the removal does not have to cross the face of the antenna while it is radiating. This design does not preclude removal of an entire subarray, but this would have to be accomplished on the front or radiating portion of the antenna with the disconnection occurring from the rear. The size of the subarray resulted from three primary considerations. First, the subarray should be large enough to minimize the loss resulting from gaps between the subarrays. Second, a dimension was chosen that was workable with the LRU. Third, since it is necessary to maintain the flatness of the subarray, a dimension was chosen that coincides with the 60° structure load path and matches the hard points of the structure. Figure 7-47 is the basic subarray design with an example of an eight-amplitron LRU. This subarray would actually be completely covered with 1840 amplitrons. The basic subarray size and LRU size would be identical throughout the 1 km antenna. Since there are eight steps or eight power quantizations from the center of the antenna to the edge, there are eight different feed systems for the LRU's. The subarrays have slotted waveguide radiating apertures with dimensions corresponding to the transmis'sion frequency of 2.45 GHz. The current design uses amplitrons in a cascade arrangement, where one amplitron provides the drive for the next amplitron in the chain. A maximum of eight and a minimum of one are cascaded. Each LRU has a driver amplifier and a phase controller that allows phase control at the LRU level. Also, each amplitron has an adjustment for phase control. The waveguide metal thickness was chosen as 0.5 mm to minimize the weight of the antenna. Manufacturing tolerances for the slot dimensions will be on the order of 0.025 to 0.050 mm. Although the subarray has been sized at 20 x 23 m, this design is one of many that can satisfy the requirements of the microwave system. 7. 3. 6 PHASE CONTROL One of the most critical technology items necessary for the microwave power system is the phase control subsystem. Although mechanical means of pointing the 1 km planar phased array antenna may be achievable to within approximately ±1 arc min, overall efficiency and safety for an acceptable system will demand greater beam pointing accuracy. Beam pointing and focusing accuracies in the single digit arc second range require electronic means of phase control. Phase relationships between elements of the planar array determine the transmitted beam pattern, directivity, and degree of side lobe suppression. These factors have a significant effect on overall system efficiency. Since there are many variable parameters that potentially change the phase relations and, thus, the transmitted beam pattern, a positive adaptive
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