1. The microwave beam remains focused or pointed at the receiving rectenna with a change in the angular position of the rectenna with respect to the face of the transmitting antenna. In the SPS transmitting antenna subarray, this behavior would solve the problem caused by ripples in the transmitting antenna surface that are the result of sudden temperature changes, for example, that caused by the satellite coming out of eclipse by the Earth. Under these circumstances, the individual subarray has to be kept either very small or its pointing adjusted by using mechanical jacks placed under the corners of the subarray, if serious efficiency loss in power transmission is to be avoided. One of the many possibilities for distortion of the array and indicating the pointing problem the subarray may encounter is depicted in Fig. 9. The approach used for electronic steering in the ground-based phased array would solve this problem and permit making subarrays very large in area if that were desired. 2. The design approach allows a first order (linear taper) focusing or defocusing of the beam, assuming an undeformed surface, or conversely, a first order phase correction for a deformed surface of the type that would be expected from different temperatures on the front and back of the surface. The first use is not applicable to the SPS subarray but the second is because a large subarray is likely to be distorted because of different temperatures between front and back. The nature of the distortion will be well known so that appropriate inputs to the digital phase control matrix can be made. This kind of distortion is also shown in Fig. 9. 3. The design approach allows correction for a linear expansion or contraction of the array caused by temperature changes. This, of course, is directly applicable to conditions in the subarray where the individual radiation modules are attached to a frame which would lengthen or shorten with temperature change. A simple correction of this would permit a much wider choice of structural materials since the coefficient of expansion with temperature would not be a primary consideration. A more detailed description of the proposed subarray design approach based upon the experience of the ground-based phased array follows. The angular position of a microwave beacon located at the center of the rectenna relative to the bore sighted axis of the transmitting antenna is sensed by two interferometers, one for the X direction and one for the Y direction. This arrangement is shown in Fig. 10 for the ground array. In the SPS application, the interferometers could probably be strapped down to the frame of the subarray. The frequency of the beacon is located far enough away from the frequency of the microwave beam transferring the power so that the microwave filtering requirements can be met by the attenuation in the waveguide arms of the interferometer, aided with a rotation of the polarization of the signal beam 90° from that of the linearly polarized power beam. The error signals from the interferometers are used to supply a digital signal to a row and column matrix, one signal for the X direction and one for the Y direction, as
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