C. Wooten Tracking & Communications Development Division IV-C-2-b RADIO FREQUENCY INTERFERENCE CTJ RATIONALE A solar power satellite (SPS) must be compatible with national and international users of the RF spectrum. The microwave generator, which will generate a high power main carrier frequency plus spurious noise near the carrier frequency and lower level harmonics, will be the main source of interference. Other sources of interference from the SPS will be power transfer equipment such as switches and slip rings, high voltage corona and high voltage arcs. Possible sources of susceptibility will be encountered in the monitoring and control links from the satellite power system to earth. These RF links will require sensitive receivers located near the high power DC to RF converters. The frequency contemplated for use is 2450 MHz which has been allocated for industrial use. The DC to RF converters being considered for this application will require comprehensive test programs for the frequency spectrum emitted. This section is the result of an evaluation of the RFI (radio frequency interference) considerations related to the design of an SPS. Interference to other users of the frequency spectrum (such as commercial radio, television, communications, navigation and radar equipments) may result from the operating frequency of the SPS as well as any spurious or harmonic frequencies it may generate. In the limited time available, this evaluation concentrated primarily on a review of existing documentation relevant to this problem. However, some limited laboratory testing was conducted to determine typical electromagnetic spectrum user equipment susceptibilities to such interference as the SPS would generate. The transmission of solar energy to earth from orbital altitude by a microwave beam is a four-fold process: (1) conversion of prime source of energy into DC (direct current) power; (2) conversion of DC power into microwave power; (3) forming the microwave power into a narrow beam for transmission to the earth, and (4) collection and reconversion of microwave power into DC power. This evaluation of RFI considerations is concerned primarily with processes 2 and 3, since these may generate and radiate significant interference power which may affect other users of the electromagnetic frequency spectrum. The SPS requirement for a converter that uses DC and converts this DC to high power microwave energy makes linear-beam tubes and crossed- field tubes theoretically acceptable for this operation. Some examples of linear beam tubes are klystrons and TWT's (traveling wave tubes). Examples of crossed-field tubes are magnetrons and amplitrons. (2) DEFINITION The linear-beam tubes exhibit better RFI characteristics than crossed-field tubes. In a typical linear-beam tube, spurious noise is down from the fundamental by -90 dB, while spurious noise is down only by -30 to -60 dB from the fundamental in a typical crossed-field tube. It was noted in an article from "Microwaves", entitled, "Controlling Interference in
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