Satellite Antennas
Thursday, November 5th, 2009Antennas are essential components of a satellite system. They are located aboard the satellites and as part of the ground equipment suites. The signal transmitted from a ground terminal antenna up to a satellite is called an uplink, and the transmission from a satellite to a ground terminal antenna is called a downlink. The frequencies of the uplink and downlink are never the same. The uplink frequency is normally higher. The reason for this, it is easier to generate radio frequency power on the ground rather than aboard the satellite where weight and power are limited. For a large dish reflector antenna on the ground, using the higher frequency (which has shorter wavelength) for the uplink will maximize the signal power that is transmitted to the satellite. This is important because the satellite, in comparison, will be more disadvantaged in its ability to strongly receive and transmit signals. Again, the larger ground antenna will have the advantage to more strongly collect the weaker, lower frequency downlink signals transmitted by the satellite.
Communications Satellites
Friday, August 1st, 2008Our daily lives are affected regularly by communications satellites. Communications satellites provide an effective way to connect people and business from the most remote areas of the world to civilization. Many forms of business use communications satellites, like newspapers, gas stations, Internet service providers and even emergency management officials.
What makes communications satellites so useful is the frequency range at which these systems operate. Communications satellites operate near or in the microwave frequency range. This frequency range is optimum for carry large quantities of data. They are also best suited for line of sight (LOS) communications. LOS means the antennas have to see each other for the signal to be received. These frequencies are not reflected or absorbed by the Earth’s atmosphere like in the case of HF signals reflected by the ionosphere.