these lobes are suppressed by the nulls of the subarray pattern. (2) SAME SUBARRAYS SPREAD OUT ON REGULAR GRID (See Figure IV-C-1-3) If the subarrays are spread out over a wider area, the beamwidth of the array becomes more narrow, approximately equal to 2A/D, where D is the new, larger diameter. The gain of the beam remains n4irA/A2 where A is the active area, i.e. the total subarray area. The transmitted power within the beam is reduced, since the peak of the beam is the same but the beam is narrower. This lost power is found to be radiated into the sidelobe region. If the subarray spacing is regular (like a rectangular grid), the added sidelobe power will appear in discrete lobes, called grating lobes. The array factor grating lobes move inward because of the increased subarray spacing and, therefore, they move out from under the nulls of the subarray pattern. (Figure IV-C-1-3) (3) SAME SUBARRAYS SPREAD OUT AT RANDOM (See Figure IV-C-1-4) If the subarray spacings are randomized, the added power in the sidelobes will be spread out uniformly with noise-like peaks. If the subarrays are spread out over an area twice as large as the subarray area, half of the power under the beam will be radiated into the sidelobes since this power is spread over a wide area, it cannot be effectively collected in a ground rectenna of fixed size. When the subarray spacing is periodic, the power will occur in many lobes about the mainbeam and this too will be expensive to collect. The effects of "splitting" a large antenna aperture can be seen in both the main beam and the sidelobes. In the case of an array of smaller antennas, each smaller antenna radiates over a larger area than does a large antenna. (The smaller the diameter, the broader the beamwidth of the individual antenna). The energy in the sidelobes of an array increases as the spacing between antennas increases. The conclusions reached are that "splitting" into many small antennas will increase sidelobe levels and will increase losses in the main beam so that antenna efficiency is prohibitively degraded.
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