Anomalous signal fluctuations due to ionospheric scintillation at 1.5 GHz appear occasionally on earth‐space paths in maritime satellite communication. With regard to the characteristics of ionospheric scintillations at gigahertz frequencies, few data are available in the middle latitude region. This paper describes the results of 1.5‐GHz scintillation measurements at Yamaguchi, Japan. Measurements were carried out by receiving a 1.5‐GHz beacon signal from the MARISAT satellite over the Indian Ocean with an elevation angle of 17.3°. In 13 months of measurements, very severe scintillation with peak‐to‐peak fluctuations exceeding 30 dB was observed in the equinoctial month, and a number of spike‐type scintillations were also observed, particularly at night. Scintillation characteristics, such as diurnal and seasonal variations, amplitude distribution, spectrum, and depolarization are discussed.
Several prediction methods for rain attenuation presented so far are evaluated using a common long‐term data base (total 124 sets of measurements) for oblique propagation paths with frequencies of from 10 to 20 GHz, and an improved prediction method reflecting the evaluation results performed is proposed. The evaluation results indicate that CCIR methods give relatively high precision, although in this respect, there is not such a great difference from other methods. The method proposed here includes a rain area size parameter as a function of rain rate for 0.01% of the time so as to minimize the prediction error. It is verified that the method thus obtained gives the best precision, at the present time, for predicting rain attenuation on Earth‐to‐space propagation paths at 10–20 GHz.
Compensation techniques for rain depolarization in satellite links are discussed from the viewpoint of system configuration, performance, and technical feasibility. The compensator using two rotatable polarizers has sufficient performance at microwave region. Two types of compensators, as combination of 90° and 180° polarizers and a combination of two 90° polarizers, were developed and tested. Satisfactory results were obtained at 4‐GHz band by using the INTELSAT satellite. The compensation system for an operational use is also presented in this paper.
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