Figure 6-23. SPS Incremental Cost vs. Subarray Size frequency of 2.45 GHz is given in Section 2, supported by material in Sections 3, 4 and 10. 6.5 SUBARRAY LAYOUT Locating the tubes and the radiating waveguides within a subarray presents a topology problem in that the "natural" flow of rf power is unidirectional in a straight line whereas the subarray boundary constraint requires that the rf power be confined to a somewhat rectangular area. Dimensions of various components must be properly related. For example, the waveguide width must be a multiple of the thermal radiator diameter in order that the input to each waveguide be located close to its tube. The subarray width is also related to the thermal radiator width and the method of terminating the waveguide rows. Figure 6-24 demonstrates three subarray layout concepts. In general, a good subarray layout approach should have the minimum amount of transmission lines, maximum aperture utilization, near rectangular boundaries for mechanical reasons, and minimum use of active lossy components such as high power phase
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