flector; 11GHz to 14GHz band. The feed is a high performance corrugated the spillover noise due to the spillover from the feed; the receiver horn. The offset reflector configuration lends itself to deployment noise. The first component may be due to natural sources or to man and portable designs have been produced where the offset reflector made interference. The natural noise emitters are the earth and sea folds for transportation. absorption, galactic noise, isotropic background radiation, quantum Cost is the main driver for small earth station antennas for mass noise and absorption due to the oxygen and water vapour in the market applications. Receive only terminals in the 4/6GHz band for 17/14 Antennas Figure 17.15 Multiple spot beams generated by an array feed on a space craft data or TV reception are usually symmetric prime focus paraboloid 17.5.3.2 Spot beams which are made by spinning an aluminium sheet. In the 11GHz communication band or the 12GHz DBS band, prime focus offset Spot beam antennas are required to produce a beam covering a small reflectors made from fibreglass moulds are popular. A simple open- region of the earth's surface. The angular width of the beam is ended waveguide type feed is incorporated on a sturdy feed support inversely proportional to the diameter of the antenna. Size consider- with the first stage low noise converter incorporated directly into the ations virtually dictate that some form of deployable mechanism is feed. There is considerable interest in making flat-plate array an- needed on the satellite and this leads to the use of offset reflectors tennas which can be mounted flush against buildings and incorpor- with a dual-mode or corrugated feed horn. The constraints of the ate electronic scanning to look onto the satellite signals. The launcher mean that the maximum size for a solid reflector is about technology for electronic scanning is available from military radars 3.5 metres. Larger reflectors can only be launched by using some but not so far at a price which is acce