MICROWAVE POWER TRANSMISSION SYSTEM G. D. Arndt The SPS microwave system has DC-RF power converters feeding a 1-km- diameter phased array antenna with a 10-decibel (dB) Gaussian illumination taper across the array surface. This system, as described on pages 25-46 of the SPS Reference System Report, D0E/ER-0023, dated October 1978, has not been significantly altered to date (May 1979). There are, however, two microwave areas with new analyses available now: 1) scattered power as a function of electrical and mechanical tolerances, and 2) grating lobe characteristics when the phase control system conjugates at the power module (tube) level rather than at the subarray level. SCATTERED POWER AT 2450 MHz Microwave interference with communications and navigation systems and radio astronomy will come primarily from three spacetenna sources: sideband radiation from the 2450-MHz main power beam, harmonics of 2450 MHz generated by the DC-RF converter tubes, and tube noise outside the IMS frequency band (2450 ± 50 MHz). In addition, there will be reradiation and reflections from the rectenna. A considerable amount of power at 2450 MHz will be scattered into the side lobes due to electrical and mechanical tolerances within the antenna. Figure 1 gives the microwave power lost due to these tolerances; i.e., 2% tube failures, 10° phase error, 3 arcmin subarray tilt, ±1 dB amplitude error across the subarray or power module surface, 1 arcmin antenna tilt, and a 0.25-inch mechanical spacing between the subarrays. Tube failures produce the largest loss in rectenna power (268 MW) because of the reduction in antenna area and in the amount of transmitted power. Random phase errors and 3 arcmin random subarray tilt each produce 188 MW of scattered power. The other error sources combine to scatter about 100 MW of power. There are two types of errors within the SPS phase control system which indirectly affect astronomers:
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