论文部分内容阅读
卫星广播电视地面接收站通常由天线、馈源、低噪声下变频器和接收机组成,前两部分又称为室外单元。天线是卫星广播电视地面接收站的一个重要组成部分,这是和卫星广播电视的特点分不开的。首先卫星广播电视信号的传输使用超高频频段,频率之高,频带之宽,都不是一般天线所能胜任的,通常需使用微波抛物面天线。大型抛物面天线的口径可达几十米,小的天线口径也在一米左右。抛物面天线的加工制造要求较高,需要专用的工装设备。因此这类天线的造价较高,从而使地面接收站的造价也相应提高.例如一个6m的C波段的地面接收站天线的造价要占全站造价的70～80％,因此采用高效率的天线或者减小天线的口径就能大大降低地面站的建造费用。卫星距地面接收站的距离甚远,由卫星传输到地面站的信号是非常微弱的。这就要求天线有很高的增益,而且要求天线有很低的噪声温度。天线的增益与天线的噪声温度之比称为天线的优值。采用微波面天线能获得较高的天线优值。同样,为了降低系统的噪声温度,必须减少馈线损耗,所以卫星广播电视地面站
Satellite radio and television terrestrial receiving stations usually by the antenna, feed, low noise downconverter and receiver components, the first two parts, also known as outdoor unit. Antenna is an important part of satellite radio and television ground receiving station, which is inseparable from the characteristics of satellite radio and television. First, the transmission of satellite radio and television signals using ultra-high frequency band, high frequency, wide band, are not generally capable of the antenna, usually using a microwave parabolic antenna. Large parabolic antenna diameter up to tens of meters, a small antenna diameter is about one meter. Parabolic antenna processing and manufacturing requirements, require special tooling equipment. Therefore, the cost of such antennas is high, so that the cost of the ground receiving station also increases accordingly, for example, a 6m C-band ground receiving station antenna costs 70-80% of the total cost of the station. Therefore, Or reduce the diameter of the antenna can greatly reduce the cost of ground station construction. The satellite is far from the ground receiving station and the signal transmitted by the satellite to the ground station is very weak. This requires a very high gain antenna, but also requires a very low noise antenna temperature. The ratio of the gain of the antenna to the noise temperature of the antenna is called the antenna’s merit. The use of microwave antenna can get a higher antenna excellent value. Similarly, in order to reduce the noise temperature of the system, it is necessary to reduce the feeder loss, so the satellite radio and television ground station