It is well known that weather conditions affect the performance of satellite broadcasting receiving systems. For example, snow accretion on antennas degrades the receiving performance seriously because it reduces received signal power and also can increase antenna noise. Since effects of the weather are considered to differ for various types of receiving antenna, an investigation on this phenomenon is very important. A study on weather effects to three types of satellite broadcasting receiving antenna, a planar antenna, a center-fed parabolic reflector antenna, and an offset parabolic reflector antenna, is presented in this paper. Since the performance of receiving antennas can be determined by a parameter G/T, a long-term and continuous measurement of G/T must be performed. Furthermore, the measurement of more than one receiving system should be performed simultaneously. Also, the measurement should be performed in a snowy area (in winter) and a rainy area (in the other seasons) to evaluate the effect of the weather. To fulfil the criterion, a continuous measurement system of G/T has been built in Hokkaido University, Sapporo. Sapporo, which is located at latitude 42 degrees north, has a long and snowy winter, and also has rainy days in the other seasons so that we can evaluate the effect of weather. Using this measurement system, cumulative distributions of measurement results are obtained so that the performance of different types of receiving system can be evaluated. In this paper, some considerations on the noise level are also discussed briefly to evaluate the performance degradation of the receiving systems.

Weather conditions affect the performance of satellite broadcasting receiving systems. For example, snow accretion on antennas degrades G/T seriously because it reduces received signal power and also can increase antenna noise. We need a continuous measurement of G/T to evaluate the effect of the weather conditions to the satellite broadcasting receiving systems. However, a conventional method cannot perform the continuous measurement because the antenna under test must be oriented in a specific direction (to the zenith) to obtain a noise level in a satellite broadcasting channel. This paper presents the continuous measurement of G/T for the satellite broadcasting receiving systems. We describe details of the measurement method. In our measurement system, a standard antenna is placed at the inside of a room in order to prevent the weather conditions from affecting the gain of the standard antenna. The power flux density at the inside of the room is different from that at the outside where the antennas under test are placed. Employing the effective gain of the standard antenna, we take the difference of the power flux density into account. Moreover, we propose a method to estimate the noise level in the satellite broadcasting channel from the values at the outside of the channel, and clarify the accuracy of the noise estimation. Then, we show measurement results of the G/T values for several receiving systems. From these results, we show that the G/T measurement system has high precision. Also, from the specifications of the antenna gain and typical values of the noise figure, it is expected that the measurement system has a sufficient accuracy.