single antenna design is to be utilized for each subarray and a single subarray size is utilized through the antenna, element size and hence power density cannot be selected arbitrarily. Considerable leeway is available in selecting waveguide width, which then determines slot spacing; however, in attempting to obtain the maximum efficiency for a narrow bandwidth this width parameter becomes more stringent compared to the design of communication antennas. The guide sizing and slot spacing in this study was primarily for the purpose of weight estimating and secondarily to provide some insight into manufacturing and assembly techniques. However, it has led to the conclusion that the antenna design should be investigated in detail analytically and experimentally to establish guide size and slot spacing for maximum efficiency. Then the exact subarray size and reasonable power density variation can be established. In examining how the subarrays could be divided for power density requirements, consideration was given to the possibility of using common parts in elements of different areas. Only the feedguide and guidewalls are usable in this manner. Each change in radiating area requires different slot coupling factors and hence different slot locations. The walls are simply different lengths (measuring and cutting) which should not present too big a problem. This leaves only the feedguide as a multiple usage part. The subarray size investigated was 100 m2 (10m X 10m). Smaller subarrays tend to improve phase control and efficiency but increase cost, therefore, this is a reasonable place to work. Also, the cost vs weight tradeoff curve shows the 100 m2 as the preferred size. The support structure design evolved toward a subarray side ratio of 0.866 to accommodate an equiangular triangel layout of mechanical pick up points. This could be accommodated with no apparent loss in efficiency when compared to a square subarray arrangement and there doesn't appear to be any change in weight. It is noted that the subarray layout was not reshaped for this configuration. e. TECHNOLOGY STATUS The technology base for designing and fabricating the proposed arrsy elements is readily available. The following steps should be taken to achieve an antenna design capable of being assembled in space and approaching 95% (worst case) efficiency. (1) Perform analysis, design and fabrication using current techniques to determine maximum achievable efficiency. (2) Investigate compromise designs and determine efficiency loss incurred to reduce cost and/or facilitate on-orbit manufacturing and/or assembly. f. WEIGHTS The element sizing and power density levels used for weight estimates are given in Table IV-C-3-1. This is based upon a nominal guide width of 10 cm and no consideration is given to allowable radiator length in terms of integral slot spacings. A breakout of weight per part for a 20 kW/m2 subarray is given in Table IV-C-3-2. As expected, the big weight factor is the face sheets.
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