where Ro is the distance from the center of the satellite antenna to the field point on the ground. The third term (X„ + Y^)/2R0 in Eq. 5 can be neglected because the pilot beam phase conjugating signal has the effect of eliminating this spatial variation. Thus, the two-term approximation is adequate for an SPS array. In the case of a circular symmetric antenna, the path length can be written in polar coordinates as When considering a complete antenna aperture, the composite electric field at a point on the ground is obtained by integrating the point source contributions oyer the surface of the antenna. If the elecric field taper across the antenna is given by Ea(Xa, Ya) and the ground field point is in the Fraunhafer, or far-field, region of the one kilometer antenna, the resulting field at the ground can be written
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