antenna. For the SPS reference system parameters, the power density at rectenna boresight is calculated to be 23.6 mW/cm2 for a perfect antenna. The rectenna collection efficiency for the 10 dB Gaussian taper is from simultation results, 95.18% for a 10 km diameter rectenna. Summarizing, the 10 dB taper is very important in terms of collection efficiency (95.18% versus 83.8% for uniform illumination), but has limited impact upon main beam and grating lobe peaks (23.6 mW/cm2 versus 26 mW/cm2 for uniform illumination). This 10% difference in giant lobe peaks is small in comparison to the effects of antenna tilt which will be shown to have orders of magnitude impact upon grating lobe intensities. Rectangular Subarray Pattern (/3) The third antenna function f3 is the pattern from a single subarray of dimensions Lx and LY. Each subarray has a uniform field distribution across its surface as given by This subarray power density pattern is contour plotted in Fig. 7, using the SPS parameters of Lx = LY = 10.4328 m. The subarray's X and Y axes are projected onto the ground pattern. Peak magnitudes on the .Y-axis fall (due to the denominator, Kx^Lx/2) approximately at a \/X„ rate, while the off-axis peaks decrease at \/XJY„. Thus, off-axis magnitudes are given by the dB sum of the two on-axis dB components. For example, the overall pattern is down 13 dB at X„ = 635 km which corresponds to -26 dB at Xo, Ya = 635 km. Since the composite grating lobes are directly proportional to the subarray pattern as given in Eq. 10, the off-axis grating lobes will be several orders of magnitude lower than those on the X and Y axes. Using the SPS reference parameters in Eq. 25, the subarray pattern null lines occur at integral multiples of 423 km from the rectenna boresight. The condition for subarray nulls from Eq. 25 is identical to the condition for grating lobe occurrence given in Eq. 15.
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