each of these two geographical sites, the general type of DoD C-E system such as voice communications, telemetry, radar, etc.; the C-E system function (e.g., air traffic control, mobile communications, research radar, etc.); along with the expected range of system parameters such as receiver sensitivity, bandwidth, and antenna gain are examined. Basic calculations of power levels of the SPS transmission at DoD C-E system receivers indicate interaction with the carrier and with the harmonics of the carrier. Calculations are based on SPS technical characteristics as given in Reference 1. Such interactions can be greatly reduced by limiting operation of C-E systems to certain frequencies and maintaining distance separations. For example, based on expected sensitivities of C-E systems at the DoD locations and their associated antenna gains, in-band (SPS carrier) EMC will be achieved when frequency separation (Af) -50 MHz and a distance separation of more than 25 km exists between the SPS satellite transmitting antenna pattern and the DoD C-E receiving system. In the case of harmonics (the out- of-band case), assuming the harmonics being 100 dB below the carrier, a Af >20 MHz and a distance separation of more than 25 km are necessary. A number of factors are not included in these calculations, however, that could potentially result in operational constraints that are much more restrictive. Component aging (degradation) may affect both satellite radiated carrier spectrum and antenna beam formation. The element pattern of the array at the harmonics is not known and most certainly will be different than that at the carrier frequency. Hence, the antenna pattern (including harmonic grading lobe positions) will be different than that of the fundamental frequency. Further study and measurements in these areas are required. Noise frequencies radiated from the SPS satellite transmitter and the scattering and reradiation of frequencies at the earth rectenna could present a potential EMC problem to DoD C-E systems if not controlled. For example, in the SPS antenna array, each of the 103,000 klystrons will generate noise. The noise from each klystron will be noncoherent with the others. Reference 1 cites the use of phase control between klystrons to suppress near-in noise and multiple-cavity klystrons to suppress other noise. The adequacy of these controls for all noise emissions may require further development. Concern for the level of noncoherent noise suppression of the total array noise is of vital importance because the total array pattern will not be realized for this noncoherent noise. The beam pattern will be much broader, on the order of one degree, as found by the elements fed by one klystron in a power module. The power density of the noise in this broad, de-focused, array pattern will be reduced by the level of the noise in a klystron to that of the carrier. This broad radiation pattern would cover a radius about the rectenna of approximately 500 km. This characteristic of large phased arrays has been noted in military systems. Figure 1 illustrates a measured antenna pattern of a large phased array fed by 32 cross-field amplifiers. The broad antenna pattern formed by the array for the noncoherent noise is clearly illustrated. Concept Development and Evaluation Program: Satellite Power System, D0E/ER-0023, January 1979.
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