tube. Instead it radiates approximately all of its power. A small percentage ( ) of its power must be dumped in a load to yield realizable slot coupling. Figure 6-25 shows two row terminating approaches using Layout No. 3 of Figure 6-24. The staggered end approach has identical waveguide rows. The rows are staggered horizontally by 0.48m in a periodic fashion. Each row contains seven waveguides having 0. 12m x 1. 92m dimensions and one waveguide having 0. 12m x 2. 35m dimensions. The subarray width is 17. 2m, a multiple of the radiator diameter of 48 cm for the amplitron. Each row is only 15. 8m long and, hence, the subarray aperture efficiency is In order to make the 2.35m long waveguide uniformly distributed, ten percent of its power must be dumped in a load. The efficiency associated with the dumped power is: The total aperture efficiency for the staggered edge approach is: The aperture efficiency for the non-staggered edge approach was computed to be 94 percent, which includes the effect of loss of aperture at the left edge, aperture taper at the right edge and ten percent dumped power in the right edge waveguides. Peak grating lobes were found to be -21.1 dB for the staggered approach and below -22 dB for the non-staggered approach. Figure 6-26 shows two of the slotted waveguide designs required.
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